CA2363981C - Method and apparatus for communicating data in a wellbore and for detecting the influx of gas - Google Patents

Abstract

The present invention relates to a borehole acoustic communication system. The apparatus of the invention comprises a first transceiver at a first communication node and a second transceiver at a second communication node. The data is transmitted in a wellbore between the first transceiver and the second transceiver through a communication channel.

Description

_ 1 _ 2 1. Field of the Invention:

3 The present invention relates to:

4 (a) a transducer which may be utilized to transmit and receive data in a wellbore;
6 (b) a communication system for improving the communication of data 7 in a wellbore;
8 (c) one application of the transducer in a measurement-while-drilling g system; and (4) one application of the transducer and communication system to 11 detect gas influx in a wellbore.
12 2. Background of the Invention:
13 One of the more difficult problems associated with any 14 borehole is to communicate intelligence between one or more locations down a borehole and the surface, or between downhole locations 16 themselves. For example, communication is desired by the oil industry to 17 retrieve, at the surface, data generated downhole during drilling operations, 18 including during quiescent periods interspersing actual drilling procedures 19 or vYhile tripping; during completion operations such as perforating, fracturing , and drill stem or well testing; and during production operations 21 such as reservoir evaluation testing, pressure and temperature monitoring.
22 Communication is also desired in such industry to transmit intelligence from DOCKET NO. 424-3666-CIP

1 the surface to downhole tools or instruments to effect, control or modify 2 operations or parameters.
3 Accurate and reliable downhole communication is particularly 4 important when data (intelligence) is to be communicated. This intelligence often is in the form of an encoded digital signal.
6 One approach has been widely considered for borehole 7 communication is to use a direct wire connection between the surface and 8 the downhole location(s). Communication then can be via electrical signal 9 through the wire. While much effort has been expended toward "wireline"
communication; this approach has not been adopted commercially because 11 it has been found to be quite costly and unreliable. For example, one 12 difficulty with this approach is that since the wire is often laid via numerous 13 lengths of a drill stem or production tubing, it is not unusual for there to be 14 a break or a poor wire connection which arises at the time the wire ~ assembly is first installed. While it has been proposed (see U.S. Patent No.
16 4,215,426) to avoid the problems associated with direct electrical coupling 17 of drill stems by providing inductive coupling for the communication link at 18 such location, inductive coupling has as a problem, among others, major 19 signal loss at every coupling. It also relies on installation of special and complex drillstring arrangements.
21 Another borehole communication technique that has been 22 explored is the transmission of acoustic waves. Such physical waves need 23 a transmission medium that will propagate the same. It will be recognized 24 that matters such as variations in earth strata, density make-up, etc., render the earth completely inappropriate for an acoustic communication DOCKET NO. 424-3666-CIP

~ -3-1 transmission medium. Because of these known problems, those in the art 2 generally have confined themselves to exploring acoustic communication 3 through borehole related media.
4 Much effort has been expended toward developing an appropriate acoustic communication system in which the borehole drill stem 6 , or production tubing itself acts as the transmission medium. A major 7 problem associated with such arrangements is caused by the fact that the 8 configurations of drill stems or production tubing generally vary significantly 9 Lengthwise. These variations typically are different in each hole. Moreover, a configuration in a particular borehole may vary over time because, for 11 example, of the addition of tubing and tools to the string. The result is that 12 there is no general usage system relying on drill stem or production tubing 13 transmission that has gained meaningful market acceptance.
14 Efforts have also been made to utilize liquid within a borehole as the acoustic transmission medium. At first blush, one would think that 16 use of a liquid as the transmission medium in a borehole would be relatively 17 simple approach, in view of the wide usage and signficant developments 18 that have been made for communication and sonar systems relying on t9 acoustic transmission within the ocean.
2p Acoustic transmission via a liquid within a borehole is considerably 21 different than acoustic transmission within an open ocean because of the 22 problems associated with the boundaries between the liquid and its 23 confining structures in a borehole. Criteria relating to these problems are 24 of paramount importance. However, because of the attractiveness of the concept of acoustic transmission in a liquid independent of movement DOCKET NO. 424-3666-CIP

1 thereof, a system was proposed in U.S. Patent No. 3,964,556 utilizing 2 _ pressure changes in a non-moving liquid to communicate. Such system 3 has not been found practical, however, since it is not a self-contained 4 system and some movement of the liquid has been found necessary to transmit pressure changes.
6 . In light of the above, meaningful communication of intelligence 7 via borehole liquids has been limited to systems which rely on flow of the 8 liquid to carry on acoustic modulation from a transmission point to a 9 receiver. This approach is generally referred to in the art as MWD (measure while -drilling). - Developments relating to it have been limited to 11 communication during the drilling phase in the life of a borehole, principally 12 since it is only during drilling that one can be assured of fluid which can be 13 modulated flowing between the drilling location and the surface. Most MWD
14 systems are also constrained because of the drilling operation itself. For example, it is not unusual that the drilling operation must be stopped during 16 . communication to avoid the ,noise associated with such drilling.
Moreover, 17 communication during tripping is impossible.
18 In spite of the problems with MWD communication, much 19 research has been done on the same in view of the desirability of good borehole communication. The result has been an extensive number of 21 patents relating to MWD, many of which are directed to proposed solutions 22 to the various problems that have been encountered. U.S. Patent No.
23 . 4,215,426 describes an arrangement in which power (rather than 24 communication) is transmitted downhole through fluid modulation akin to MWD communication, a portion of which power is drained off at various DOCKET NO. 424-3666-CIP

s ~ _ 1 locations downhole to power repeaters in a wireline communication 2 transmission system.
3 The development of communication using acoustic waves 4 propagating through non-flowing fluids in a borehole has been impeded by lack of a suitable transducer. To be practical for a borehole application, 6 - such a transducer has to fit in a pressure barrel with an outer diameter of 7 no more than 1.25 inches, operate at temperatures up to 150°C and 8 pressures up to 1000 bar, and survive the working environment of handling 9 and running in a well. Such a transducer would also have to take into consideration the significant differences between communication in a non-11 constrained fluid environment, such as the ocean, and a caned fluid 12 arrangement, such as in a borehole.
13 The development of reliable communication using acoustic waves 14 propagating through non-flowing fluids in a borehole has been impeded by - ~ . the fact that the borehole environment is extremely noisy. Moreover, to be 16 practical, an acoustic communication system using non-flowing liquid is 17 required to be highly adaptive to variations in the borehole channel and 18 must provide robust and reliable throughput of data in spite of such 19 variations.
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2 THE TRANSDUCER: The present invention relates to a practical borehole 3 acoustic communication transducer. It is capable of generating, or 4 responding to, acoustic waves in a viscous liquid confined in a borehole.
Its design takes into consideration the waveguide nature of a borehole. It 6 has been found that, to be practical, a borehole acoustic transducer has to 7 . generate, or respond to, acoustic waves at frequencies below one kilohertz 8 with bandwidths of tens of Hertz, efficiently in various liquids. It has to be 9 able to do so while providing high displacement and having a lower mechanical impedance than conventional open ocean devices. The 11 transducer of the invention meets these criteria as well as the size and 12 operating criteria mentioned above. .
13 The transducer of the invention has many features that 14 contribute to its capability. It is similar to a moving coil loudspeaker in that movement of an electric winding relative to magnetic flux in the gap of a 16 . magnetic circuit is used to convert between electric power and mechanical 17 motion. It uses the same interaction for transmitting and receiving. A
18 dominant feature of the transducer of the invention is that a plurality of gaps 19 are used with a corresponding number (and placement) of electrical windings. This facilitates developing, with such a small diameter 21 arrangement, the forces and displacements found to be necessary to 22 transduce the low frequency waves required for adequate transmission 23 through non-flowing viscous fluid confined in a borehole. Moreover, a 24 resonator may be included as part of the transducer if desired to provide a compliant backload.
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1 The invention includes several arrangements responsible for 2 assuring that there is good borehole transmission of acoustic waves. For 3 one, a transition section is included to provide acoustic impedance matching 4 in the borehole liquid between sections of the borehole having significantly different cross-sectional areas such as between the section of the borehole 6 having the transducer and any adjacent borehole section. Reference 7 . throughout this patent specification to a "cross-sectional" area is reference 8 to the cross-sectional area of the transmission (communication channel.) 9 For another, a directional coupler arrangement is described which is at least partially responsible for inhibiting transmission opposite to the direction in 11 the borehole of the desired communication. Specifically, a reflection section 12 is defined in the borehole, which section is spaced generally an odd number 13 of quarter wavelengths from the transducer and positioned in a direction 14 opposite that desired for the communication, to reflect back in the proper communication direction, any acoustic waves received by the same which 16 are being propagated in the wrong direction. Most desirably, a multiple 17 . number of reflection sections meeting this criteria are provided as will be 18 described in detail.
1g A special bidirectional coupler based on back-loading of the transducer piston also can be provided for this purpose. Most desirably, 21 the borehole acoustic communication transducer of the invention has a 22 chamber defining a compliant back-load for the piston, through which a 23 window extends that is spaced from the location at which the remainder of 24 the transducer interacts with borehole liquid by generally an odd number of quarter wavelengths of the nominal frequency of the central wavelength of 26 potential communication waves at the locations of said window and the 27 point of interaction.
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Other features and advantages of the invention will be 2 disclosed or will become apparent from the following more detailed description. While such description includes many variations which 4 occurred to Applicant, it will be recognized that the coverage afforded Applicant is not limited to such variations. In other words, the presentation 6 is supposed to be exemplary, rather than exhaustive.
7 THE COMMUNICATION SYSTEM: The present invention relates to a g practical borehole acoustic communication system. It is capable of 9 communicating in both flowing and non-flowing viscous liquids confined in 1p a borehole, although many of its features are useful in borehole 11 communication with production tubing or a drill stem being the acoustic 12 medium. Its design, however, takes into consideration the waveguide 13 nature of a borehole. It has been found that to be practical a borehole 14 acoustic communication system has to operate at frequencies below one kilohertz with an adequate bandwidth. The bandwidth depends on various 16 - factors, including the efficiency of the transmission medium. It has been 17 found that a bandwidth of at least several Hertz are required for efficient 18 communication in various liquids. The system must transfer information in 1g a robust and reliable manner, even during periods of excessive acoustic noise and in a dynamic environment.
21 As an important feature of the invention, the acoustic 22 communication system characterizes the transmission channel when (1) 23 system operation is initiated and (2) when synchronization between the 24 downhole acoustic transceiver (DAT) and the surface acoustic transceiver (SAT) is lost. To facilitate the channel characterization, a wide-band "chirp"
26 signal, (a signal having its energy distributed throughout the candidate DOCKET NO. 424-3666-CIP

_g_ 1 spectrum) is transmitted from the DAT to the SAT. The received signal is 2 processed to determine the portion of the spectrum that provides an 3 exceptional signal to noise ratio and a bandwidth capable of supporting data 4 transmission.
As another important feature of the invention, it provides 6 two-way communication between the locations. Each of the communication 7 , transducers is a transceiver for both receiving acoustic signals from, and for 8 imparting acoustic signals to, the (preferably) non-moving borehole liquid.
9 The communication is reciprocal in that it is provided by assuring that the electrical load impedance for receiving an acoustic signal from the borehole 11 liquid equals the source impedance of such transceiver for transmitting.
12 Most desirably, the transceivers are time synchronized to provide a robust 13 communication system. Initial synchronization is accomplished through 14 transmission of a synchronization signal in the form of a repetitive chirp sequence by one of the units, such as the downhole acoustic transceiver 16 (DAT) in the preferred embodiment. The surface acoustic transceiver (SAT) 17 . processes the received sequence to establish approximate clock 18 synchronization. When communication is between a downhole location and 19 the surface, as in the preferred embodiment, it is preferred that most, 'rf not all, of the data processing take place at the surface where space is plentiful.
21 This first synchronization is only an approximation. As another 22 dominant feature, a second synchronization signal is transmitted from the 23 SAT tQ the DAT to refine such synchronization. The second synchronization 24 signal is comprised of two tones, each of a different frequency. Signal analysis of these tones by the DAT enables the timing of the DAT to be 26 adjusted into synchrony with the SAT.
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1 Although the communication system of the invention is 2 particularly designed for use of a borehole liquid as the transmission 3 medium, many of its features are usable to improve acoustic transmission 4 when the transmission system utilizes a drill stem, production tubing or other means extending in a borehole as a transmission medium. For 6 example, it provides clock correction during the time data is being 7 transmitted. Other features and advantages of the invention either will 8 , become apparent or will be described in the following more detailed g description of a preferred embodiment and alternatives.
1p THE MEASUREMENT-WHILE-DRILLING APPLICATION: While the preferred 11 embodiment of the present invention discussed herein is the utilization of the 12 communication system in a producing oil and gas well, it is also possible to 13 utilize the transducer and the communication system of the present 14 invention during drilling operations to transmit data, preferably through the drilling fluid, between (1) selected points in the drillstring, or (2) between a 16 selected point in the drillstring and the earth's surface. The present 17 . invention can be utilized in parallel with a conventional measurement-while-18 drilling data transmission system, or as a substitute for a conventional 19 measurement-while-drilling data transmission system. The present invention 2p is superior to conventim gal measurement-while-drilling data transmission 21 systems insofar as communication can occur while there is no circulation of 22 fluid in the wellbore. The present invention can be utilized for the 23 bidirectional transmission of data and remote control signals within the 24 wellbore. ' GAS INFLUX DETECTION: The transducer and communication system of 26 the present invention can also be utilized in a wellbore to detect the entry ' DOCKET NO. 424-3666-CIP

1 of natural gas into the wellbore, typically during drilling and completion 2 operations. As those skilled in the art will understand, the introduction of 3 high pressure gas into a fluid column in the wellbore can result in loss of 4 control over the well, and in the worst case, can result in a blowout of the well. Present technologies are inadequate for determining both (1) that a 5 undesirable gas influx has occurred, and (2) the location of the gas "bubble"
7. within the fluid column (bear in mind the gas influx will travel generally 8 upward in the fluid column). The present invention can be utilized to 9 determine whether or not a gas bubble is present in the fluid column, and to provide a general indication of the location of the gas bubble within the 11 fluid column. With this information, the well operator can take precautionary 12 measurements to prevent loss of control of the well, such as by increasing 13 or decreasing the "weight" (density) of the fluid column.
14 Additional objectives, features and advantages will be apparent in the written description which follows.
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The novel features believed characteristic of the invention are 3 set forth in the appended claims. The invention itself, however, as well as 4 a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an 6 illustrative embodiment when read in conjunction with the accompanying 7 drawings, wherein:
g Figure 1 is an overall schematic sectional view illustrating a 9 potential location within a borehole of an implementation of the invention;
1p Figure 2 is an enlarged schematic view of a portion of the 11 arrangement shown in Figure 1;
12 Figure 3 is an overall sectional view of an implementation of 13 - the transducer of the instant invention;
14 Figure 4 is an enlarged sectional view of a portion of the construction shown in Figure 3;
1g Figure 5 is a transverse sectional view, taken on a plane 17 indicated by the lines 5-5 in Figure 4;
1g - Figure 6 is a partial, somewhat schematic sectional view 19 showing the magnetic circuit provided by the implementation illustrated in Fgures 3-5;
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1 Figure 7A is a schematic view corresponding to the 2 implementation of the invention shown in Figures 3-6, and Figure 78 is a 3 variation on such implementation;
4 Figures 8 through 11 illustrate various alternate constructions;
. Figure 12 illustrates in schematic form a preferred combination 6 of such elements;
7 Figure 13, which is comprised of Figures 13A, 13B and 13C, is an overall sectional view of another implementation of the instant invention;
g Figure 14 is an enlarged sectional view of a portion of the construction shown in Figure 13;
11 Figures 15A-15C illustrate in schematic cross-section various 12 . . constructions of a directional coupler portion of the invention.
13 Figure 16 is an overall somewhat diagrammatic sectional view 14 illustrating an implementation of the invention, a potential location within a borehole for the same;
16 Figure 17 is a block diagram of a preferred embodiment of the 17 invention;
1 g Figure 18 is a flow chart depicting the synchronization process 19 of the downhole acoustic transceiver portion of the preferred embodiment of Figure 17;
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_14_ 1 Figure 19 is a flow chart depicting the synchronization process 2 of the surface acoustic transceiver portion of the preferred embodiment of 3 Figure 2;
4 Figure 20A, 20B, and 20C depict the synchronization signal structure;
g Figure 21 is a detailed block diagram of the downhole acoustic 7 transceiver;
g Figure 22 is a detailed block diagram of the surface acoustic g transceiver;
1p Figure 23 depicts the second synchronization signals and the 11 resultant correlation signals;
12 Figure 24 depicts the utilization of the transducer and 13. communication system in the present invention in a drillstring during drilling 14 operations to transmit data between selected locations in the drillstring;
Figures 25 and 26 are utilized to illustrate the aNalication of the 16 transducer and communication system of the present invention during 17 drilling operations for the purpose of identifying and detecting the influx of 18 gas into a wellbore fluid column; and 1 g Figures 27 and 28 are block diagram representations of an alternative data communication system for the present invention.
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2 THE TRANSDUCER: The transducer of the present invention will be 3 described with references to Figures 1 through 15.
4 With reference to Figure 1, a borehole, generally referred to by the reference numeral 11, is illustrated extending through the earth 12.
6 Borehole 11 is shown as a petroleum product completion hole for illustrative 7 purposes. It includes a casing schematically illustrated at 13 and production 8 tubing 14 within which the desired oil or other petroleum product flows. The 9 annular space between the casing and production tubing is filled with a completion liquid represented by dots 16. The viscosity of this completion 11 liquid could be any viscosity within a wide range of possible viscosities.
Its 12 density also could be of any value within a wide range, and it may include 13 corrosive liquid components like a high density salt such as a sodium, 14 potassium and/or bromide compound.
In accordance with conventional practice, a packer 16. represented at 17 is provided to seal the borehole and the completion fluid 17 from the desired petroleum product. The production tubing 14 extends 18 through the same as illustrated and may include a safety valve, data 19 gathering instrumentation, or other tools on the petroleum side ~~ the packer 17.
21 A carrier 19 for the transducer of the invention is provided on 22 the lower end of the tubing 14. As illustrated, a transition section 21 and 23 one or more reflecting sections 22 (which will be discussed in more detail 24below) separate the carrier from the remainder of the production tubing.
Such carrier includes a slot 23 within which the communication transducer DOCKET NO. 424-3666-CIP

_16_ 1 of the invention is held in a conventional manner, such as by strapping or 2 the like. A data gathering instrument, a battery pack, and other 3 components, also could be housed within slot 23.
4 ~ It is the completion liquid 16 which acts as the transmission medium for acoustic waves provided by the transducer, but any other fluid 6 , can be utilized for transmission, including but not limited to production fluids, 7 drilling fluids, or fresh or salt water. Communication between the transducer 8 and the annular space which confines such liquid is represented in Figures 9 1 and 2 by port 24. Data can be transmitted through the port .24 to the completion liquid and, hence, by the same in accordance with the invention.
11 For example, a predetermined frequency band may be used for signaling 12 by conventional coding and modulation techniques, binary data may be 13 encoded into blocks, some error checking added, and the blocks 14 transmitted serially by Frequency Shift Keying (FSK) or Phase Shift Keying (PSK) modulation. The receiver then will demodulate and check each block 16 . for errors.
17 The annular space at the carrier 19 is significantly smaller in 18 cross-sectional area than that of the greater part of the well containing, for 19 the most part, only production tubing 14. This results in a corresponding mismatch of acoustic characteristic admittances. The purpose of transition 21 section 21 is to minimize the reflections caused by the mismatch between 22 the section having the transducer and the adjacent section. It is nominally 23 one-quarter wavelength long at the desired center frequency and the sound 24 speed in the fluid, and it is selected to have a diameter so that the annular area between it and the casing 13 is a geometric average of the product of 26 the adjacent annular areas, (that is, the annular areas defined by the DOCKET NO. 424-3666-CIP

1 production tubing 14 and the carrier 19). Further transition sections can be 2 provided as necessary in the borehole to alleviate mismatches of acoustic 3 admittances along the communication path.
4 Reflections from the packer (or the well bottom in other designs) are minimized by the presence of a multiple number of reflection 6 . sections or steps below the carrier; the first of which is indicated by 7 reference numeral 22. It provides a transition to the maximum possible 8 annular area one-quarter wavelength below the transducer communication 9 port. It is followed by a quarter wavelength long tubular section 25 providing an annular area for liquid with the minimum cross-sectional area 11 it otherwise would face. Each of the reflection sections or steps can be 12 multiple number of quarter wavelengths long. The sections 19 and 21 .
13 should be an odd number of quarter wavelengths, whereas the section 25 14 should be odd or even (including zero), depending on whether or not the last step before the packer 17 has a large or small cross-section. It should 16 . be an even number (or zero) if the last step before the packer is from a 17 large cross-section to a small cross-section.
18 While the first reflection step or section as described herein is 19 the most effective, each additional one that can be added improves the degree and bandwidth of isolation. (Both the transition section 21, the 21 reflection section 22, and the tubular section can be considered as parts of 22 the combination making up the preferred transducer of the invention.) 23 A communication transducer for receiving the data is also 24 provided at the location at which it is desired to have such data. In most arrangements this will be at the surface of the well, and the electronics for DOCKET NO. 424-3666-CIP

1 operation of the receiver and analysis of the communicated data also are 2 at the surface or in some cases at another location. The receiving 3 transducer 24 most desirably is a duplicate in principle of the transducer 4 being described. (It is represented in Fgure 1 by box 5 at the surface of the well). The communication analysis electronics is represented by box 26.
6 . It will be recognized by those skilled in the art that the acoustic 7 transducer arrangement of the invention is not limited necessarily xo 8 communication from downhole to the surface. Transducers can be located 9 for communication between two different downhole locations. It is also important to note that the principle on which the transducer of the invention 11 is based lends itself to two-way design: a single transducer can be 12 designed to both convert an electrical communication signal to acoustic 13 communication waves, and vice versa.
14 ~ ~An implementation of the transducer of the invention is 15. , .. generally referred to by the reference numeral 26 in Fgures 3 through 6.
16 This specific design terminates at one end in a coupling or end plug 27 17 which is threaded into a bladder housing 28. A bladder 29 for pressure 18 expansion is provided in such housing. The housing 28 includes ports 31 19 for free flow into the same of the borehole completion liquid for interaction with the bladder. Such bladder communicates via a tube with a bore 32 21 extending through a coupler 33. The bore 32 terminates in another tube 34 22 which extends into a resonator 36. The length of the resonator Is nominally 23 .1/4 in the liquid within resonator 38. The resonator is filled with a liquid 24 . which meets the criteria of having low density, viscosity, sound speed, water content, vapor pressure and thermal expansion coefficient. . Since some of 26 these requirements ace mutually contradictory, a compromise must be DOCKET NO. 424-3666-C!P

1 made, based on the condition of the application and design constraints.
2 The best choices have thus far ben found among the 200 and 500 series 3 Dow Corning silicone oils, refrigeration oils such as Capella 8 and 4 lightweight hydrocarbons such as kerosene. The purpose of the bladder construction is to enable expansion of such liquid as necessary in view of 6 the pressure and temperature of the borehole liquid at the downhoie 7 location of the transducer.
g The transducer of the invention generates (or detects) acoustic 9 wave energy by means of the interaction of a piston in the transducer housing with the borehole liquid. In this implementation, this is done by 11 movement of a piston 37 in a chamber 38 filled with the same liquid which 12 fills resonator 36. Thus, the interaction of piston 37 with the borehole liquid 13 is indirect: the piston is not in direct contact with such borehole liquid.
14 Acoustic waves are generated by expansion and contraction of a bellows type piston 37 in housing chamber 38. One end of the bellows of the piston 16 . arrangement is permanently fastened around a small opening 39 of a horn 17 structure 41 so that reciprocation of the other end of the bellows will result 18 in the desired expansion and contraction of the same. Such expansion and 19 contraction causes corresponding flexures of isolating diaphragms 42 in windows 43 to impart acoustic energy waves to the borehole liquid on ~he 21 other side of such diaphragms. Resonator 36 provides a compliant back-22 load for this piston movement. It should be noted that the same liquid 23 which fills the chamber of the resonator 36 and chamber 38 fills the various 24 cavities of the piston driver to be discussed hereinafter, and the change in volumetric shape of chamber 38 caused by reciprocation of the piston takes 26 place before pressure equalization can occur.
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1 One way of looking at the resonator is that its chamber 36 2 acts, in effect, as a tuning pipe for returning in phase to piston 37 that 3 acoustical energy which is not transmitted by the piston to the liquid in 4 chamber 38 when such piston first moves. To this end, piston 37, made up of a steel bellows 46 (Figure 4), is open at the surrounding horn opening 39.
6 The other end of the bellows is closed and has a driving shaft 47 secured 7 . thereto. The horn structure 41 communicates the resonator 36 with the 8 piston, and such resonator aids in assuring that any acoustic energy 9 generated by the piston that does not directly result in movement of isolating diaphragms 42 will reinforce the oscillatory motion of the piston.
11 In essence, its intercepts that acoustic wave energy developed by the piston 12 which does not directly result in radiation of acoustic waves and uses the 13 same to enhance such radiation. It also acts to provide a compliant back-14 load for the piston 37 as stated previously. It should be noted that the inner wall of the resonator could be tapered or otherwise contoured to modify the 16 frequency response.
17 The driver for the piston will now be described. It includes the 18 driving shaft 47 secured to the closed end of the bellows. Such shaft also 19 is connected to an end cap 48 for a tubular bobbin 49 which carries two annular coils or windings 51 and 52 in corresponding, separate radial gaps 21 53 and 54 (Figure 6) of a closed loop magnetic circuit to be described, but 22 a greater number of bobbins could be utilized. Such bobbin terminates at 23 its other end in a second end cap 55 which is supported in position by a flat 24 spring-56. Spring 56 centers the end of the bobbin to which it is secured and constrains the same to limited movement in the direction of the 26 longitudinal axis of the transducer, represented in Figure 4 by line 57. A
27 similar flat spring 58 is provided for the end cap 48.
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" ' -21 -1 In keeping with the invention, a magnetic circuit having a 2 plurality of gaps is defined within the housing. To this end, a cylindrical 3 permanent magnet 60 is provided as part of the driver coaxial with the axis 4 57. Such permanent magnet generates the magnetic flux needed for the magnetic circuit and terminates at each of its ends in a pole piece 61 and 6 62, respectively, to concentrate the magnetic flux for flow through the pair 7 of longitudinally spaced apart gaps 53 and 54 in the magnetic circuit. The 8 magnetic circuit is completed by an annular magnetically passive member 9 of magnetically permeable material 64. As illustrated, such member includes a pair of inwardly directed annular flanges 66 and 67 which terminate 11 adjacent the windings 51 and 52 and define one side of the gaps 53 and 54.
12 The magnetic circuit formed by this implementation is 13 represented in Figure 6 by closed loop magnetic flux lines 68. As illustrated, 14 such lines extend from the magnet 60, through pole piece 61, across gap 53 and coil 51, through the return path provided by member 64, through 16 gap 54 and coil 52, and through pole piece 62 to magnet 60. With this 17 . arrangement, it will be seen that magnetic flux passes radially outward 18 through gap 53 and radially inward through gap 54. Coils 51 and 52 are 19 connected in series opposition, so that current in the same provides additive force on the common bobbin. Thus, if the transducer is being used to 21 transmit a communication, an electrical signal defining the same is passed 22 through the coils 51 and 52 will cause corresponding movement of the 23 bobbin 49 and, hence, the piston 37. Such piston will interact through the 24 windows 43 with the borehole liquid and impart the communicating acoustic energy thereto. Thus, the electrical power represented by the electrical 26 signal is converted by the transducer to mechanical power, in the form of, 27 acoustic waves.
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~ -22-1 When the transducer receives a communication, the acoustic 2 energy defining the same will flex the diaphragms 42 and correspondingly 3 move the piston 37. Movement of the bobbin and windings within the gaps 4 51 and 52 will generate a corresponding electrical signal in the coils 51 and 52 in view of the lines of magnetic flux which are cut by the same. In other 6 words, the acoustic power is converted to electrical power.
7 In the implementation being described, it will be recognized 8 that the permanent magnet 60 and its associated pole pieces 61 and 62 are 9 generally cylindrical in shape with the axis 57 acting as an axis of a figure of revolution. -The bobbin is a cylinder with the same axis, with the coils 51 11 and 52 being annular in shape. Return path member 64 also is annular and 12 surrounds the magnet, etc. The magnet is held centrally by support rods 13 71 projecting inwardly from the return path member, through slots in bobbin 14 49. The flat springs 56 and 58 correspondingly centralize the bobbin while allowing limited longitudinal motion of the same as aforesaid. Suitable 16 electrical leads 72 for the windings and other electrical parts pass into the 17 housing through potted feedthroughs 73.
18 FIG 7A illustrates the implementation described above in 19 schematic form. The resonator is represented at 36, the horn structure at 41, and the piston at 37. The driver shaft of the piston is represented at 47, 21 whereas the driver mechanism itself is represented by box 74. Fgure 7B
22 shows an alternate arrangement in which the driver is located within the 23 resonator 76 and the piston 37 communicates directly with the borehole 24 liquid which is allowed to flow in through windows 43. The windows are open; they do not include a diaphragm or other structure which prevents the 26 borehole liquid from entering the chamber 38. It will be seen that in this DOCKET N4. 424-3666-CIP

" " -23-1 arrangement the piston 37 and the horn structure 41 provide fluid-tight 2 isolation between such chamber and the resonator 36. it will be recognized, 3 though, that it also could be designed for the resonator 36 to be flooded by 4 the borehole liquid. It is desirable, if it is designed to be so flooded, that such resonator include a small bore filter or the like to exclude suspended 6 particles. In any event, the driver itself should have its own inert fluid 7 . system because of close tolerances, and strong magnetic fields. The 8 necessary use of certain materials in the same makes it prone to impairment 9 by corrosion and contamination by particles, particularly magnetic ones.
Figures 8 through 12 are schematic illustrations representing 11 various conceptual approaches and modifications for the invention, 12 considered by applicant. Fgure 8 illustrates the modular design of the 13 invention. In this connection, it should be noted that the invention is to be 14 housed in a pipe of restricted diameter, but length is not critical. The invention enables one to make the best possible use of cross-sectional area 16 . while multiple modules can be stacked to improve efficiency and power 17 capability.
1g The bobbin, represented at 81 in Fgure 8, carries three 19 separate annular windings represented at 82-84. A pair of magnetic circuits are provided, with permanent magnets represented at 86 and 87 with facing 21 magnetic polarities and poles 88-90. Return paths for both circuits are 22 provided by an annular passive member 91.
It will be seen that the two magnetic circuits of the Fgure 8 24 configuration have the central pole 89 and its associated gap in common.
The result is a three-coil driver with a transmitting efficiency (available DOCKET NO. 424-3666-CIP

1 acoustic power output/electric power input) greater than twice that of a 2 single driver, because of the absence of fringing flux at the joint ends.
3 Obviously, the process of "stacking" two coil drivers as indicated by this 4 arrangement with alternating magnet polarities can be continued as long as desired with the common bobbin being appropriately supported. In this 6 schematic arrangement, the bobbin is connected to a piston 85 which 7 , includes a central domed part and bellows of the like sealing the same to 8 an outer casing represented at 92. This flexure seal support is preferred to 9 sliding seals and bearings because the latter exhibit restriction that introduced distortion, particularly at the small displacements encountered 11 when the transducer is used for receiving. Alternatively, a rigid piston can 12 be sealed to the case with a bellows and a separate spring or spider used 13 for centering. A spider represented at 94 can be used at the opposite end 14 of the bobbin for centering the same. If such spider is metal, it can be insulated from the case and can be used for electrical connections to the 16 moving windings, eliminating the flexible leads otherwise required.
17 In the alternative schematically illustrated in Figure 9, the 18 magnet 86 is made annular and it surrounds a passive flux return path 19 member -91 in its center. Since passive materials are available with saturation flux densities about twice the remanence of magnets, the design 21 illustrated has the advantage of allowing a small diameter of the poles 22 represented at 88 and 90 to reduce coil resistance and increase efficiency.
23 The passive flux return path member 91 could be replaced by another 24 permanent magnet. A two- magnet design, of course, could permit a reduction in length of the driver.
DOCKET NO. 424-3666-CIP

1 Figure 10 schematically illustrates another magnetic structure 2 for the driver. It includes a pair of oppositely radially polarized annular 3 magnets 95 and 96. As illustrated, such magnets define the outer edges of 4 the gaps. In this arrangement, an annular passive magnetic member 97 is provided, as well as a central return path member 91. While this 6 arrangement has the advantage of reduced length due to a reduction of flux 7 leakage at the gaps and low external flux leakage, it has the disadvantage 8 of more difficult magnet fabrication and lower flux density in such gaps.
9 Conical interfaces can be provided between the magnets and pole pieces. Thus, the mating junctions can be made oblique to the long 11 axis of the transducer. This construction maximizes the magnetic volume 12 and its accompanying available energy while avoiding localized flux densities 13 that could exceed a magnet remanence. It should be noted that any of the 14 junctions, magnet-to-magnet, pole piece-to-pole piece and of course magnet-to-pole piece can be made conical. Figure 11 illustrates one 16 arrangement for this feature. It should be noted that in this arrangement the 17 magnets may includes pieces 98 at the ends of the passive flux return 18 member 91 as illustrated.
1g Figure 12 schematically illustrates a particular combination of the options set forth in Fgures 8 thorough 1 i which could be considered 21 a preferred embodiment for certain applications. It includes a pair of pole 22 pieces 101, and 102 which mate conically with radial magnets 103, 104 and 23 105. T'he two magnetic circuits which are formed include passive return 24 path members 106 and 107 terminating at the gaps in additional magnets 108 and 110.
DOCKET NO. 424-3666-CIP

1 An implementation of the. invention 2 incorporating some of the features mentioned above is 3 illustrated in Figures 13, which is comprised of 4 Figures 13A, 13B and 13C, and 14. Such implementation includes two magnetic circuits, annular magnets 6 defining the exterior of the magnetic circuit and a 7 central pole piece. Moreover, the piston is in direct .8 contact with the borehole liquid and the resonant 9 chamber is filled with such liquid.

The implementation shown in Figures 13, 11 which is comprised of Figures 13A, 13B and 13C, and 12 is similar in many aspects to the implementation 13 illustrated and described with respect to Figures 3 14 and 6. Common parts will be referred to by the same reference numerals used earlier but with the addition 16 of prime component. This implementation includes many 1~ ~ of the features of the earlier one, which features 18 should be considered as being incorporated within the 19 ~ same, unless indicated otherwise.

The implementation of Figures 13, which is 21 comprised of Figures 13A, 13B and 13C and 14 is 22 generally referred to by the reference numeral 120.

23 The resonator chamber is downhole of this piston 24 37' and its driver, in this arrangement, and is allowed to be filled with borehole liquid rather than 26 being filled with a special liquid as described in 27 cor~nection with the earlier implementation. The 28 bladder and its associated housing is eliminated and 29 the end plug is threaded directly into the resonator chamber 36. Such end plug includes a 31 plurality of elongated bores 122 which communicate the 32 borehole with tube 34 extending in to the resonator 33 36. As with the previously described implementation, 39 the tube 34 is nominally a quarter of the communication wavelength long in the resonator fluid 1 (the borehole liquid in this implementation). The 2 diameter of the bores 122 is selected relative to the 3 interior diameter of tube 34 to assure that not 4 particulate matter from the borehole liquid which is of a sufficiently large size to block such tube will 6 enter the same.

.7 It will be recognized that while with this 8 arrangement the chamber which provides a compliant 9 backload for movement of the piston 37' is in direct communication with the borehole liquid through the 11 tube 34 , acoustic wave energy in the same will not 12 be transmitted to the exterior of the chamber because 13 of attenuation by such tube.

14 Piston 37' is a bellows as described in the earlier implementation and acts to isolate the driver 16 for the same to be-described from~a chamber 38' which 17 is allowed to be filled with the borehole liquid.

18- Such chamfer 38' is illustrated as having two parts, r w 19 parts 123=and 124, that communicate directly with one another. As illustrated, windows 43' extend to the 21 annulus surrounding the transducer construction 22 without the intermediary of isolating diaphragms as in 23 the previous implementation. ~ Thus, in this 24 implementation the piston 37' is in direct contact with borehole liquid which fills the chamber 38'.

26 - The piston 37' is connected via a nut 127 27. and driving shaft 128 to the driver mechanism. To 28 this end, the driving shaft 128 is connected to an end 29 cap 48' of a tubular bobbin 49'. The bobbin 49' carries three annular coils or windings in a 31 corresponding number of radial gaps of two closed loop 32 magnetic, circuits to be described. Two of these 33 windings are represented~,at'.e128, :and 129. The third 5z,;, ..
34 winding is on the axial 'ei'de'~A'of winding 129 opposite '.' ~ ;w' '~ r:v;y - 27a -1 that of winding 128 in accordance with the arrangement 2 shown in Figure 8. Moreover, winding 129 is twice the 3 axial 1 length of winding 128. The bobbin 49' is constrained in position similarly to 2 bobbin 49' by springs 56:
3 The driver in this implementation conceptually is a hybrid of the 4 approaches~illustrated in Figures 8 and 9. That is, it includes two adjacent magnetic circuits sharing a common pathway. Moreover, the permanent 6 magnets are annular surrounding a solid core providing a passive member.
7 In more detail, three magnets illustrated in Fgure 14 at 131, 132 and i 3z.' 8 develop flux which flows across the gaps within which the windings 9 previously described ride to a solid, cylindrical core passive member 13 ø .
The magnetic circuits are completed by an annular casing i 3 3 which 11 surrounds~the magnets. Such casing 'i s3is fluid tight and acts to isolate 12 the driver as described from the borehole liquid. In this connection, it 13 includes at its end spaced from piston 37', an isolation bellows which 14 transmits pressure changes caused in the driver casing 132 to the resonator 36'. The bellows is free floating in the sense that it is not physically 16 _ connected to the tubular bobbin 49' and simply flexes to accommodate the 17 . Y , pressure changes of the special fluid in the driver casing. It sits within a 18 central cavity or borehole within a plug 38 that extends between the 19 driver casing and the wall of the resonant chamber 36'. An elongated hole or aperture connects the interior of bellows with the resonator 21 chamber:
22 A passive directional coupling arrangement is conceptually 23 illustrated by Fgures 15A-15C. The piston of the transducer is represented 24 at 220. Its design is based ow the fact that the acoustic characteristic admittance in a cylindrical waveguide is proportional to its aoss-sectional 26 area. Thb .ports. for transmission of the communicating acoustic energy DOCKET NO. 424-3666-CIP

1 to the borehote fluid are represented at 221. A second port or annular 2 series of ports 222 are located either three one-quarter wavelength section 3 (Fgure 15A) or one-quarter wavelength sections (Fgu~es 15B and C) from 4 the ports 221. The coupler is divided into three quarter wavelength sections 223-226. The cross-sectional area of these sections are selected 6 to minimize any mismatch which might defeat directional coupling. Center 7 section 224 has a cross-sectional area A3 which is nominally equal to the 8 ~ square of the cross-sectional area of sections 223 and 226 (A~ divided by 9 the annular cross-section of the borehole at the location of the ports 221 and 222. The reduced cross-sectional area of section 224 is obtained by 11 including an annular restriction 227 in the same.
12 The directional coupler is in direct contact with the backside of the 13 piston 220, with the result that acoustic wave energy will be introduced into 14 the coupler which is 180° out-of-phase with that of the desired communication. The relationship of the cross-sectional areas described 16 previously will assure that the acoustic energy which emanates from the port 17 ~ ~ . 222 will cancel any transmission from port 221 which otherwise would travel 18 toward port 222. ~' 19 The version of the directional coupler represented in Fgure 15A is full length, requiring a three-quarter wavelength long tubing, i.e., the 21 chamber is divided into three, quarter-wavelength-long sections. The 22 versions represented in Fgures 158 and 15C are folded versions, thereby 23 ' reducing the length required. That is, the version in Figure 15B is folded 24 once with the sectional areas of the sections meeting the criteria discussed previously. Two of the chamber sections are coaxial with one another. The 26 version represented in Figure 15C is folded twice. That is, alt three sections DOCKET NO. 424-3666-CIP .

' ' -30-1 are coaxial. The two versions in Figures 15B and 15C are one-fourth 2 wavelength from the port 222 and thus are on the "uphole" side of port 221 3 as illustrated. It will be recognized, though, that the bandwidth of effective 4 directional coupling is reduced with folding.
It will be recognized that in any of the configurations of Figures 6 15A-15C, the port 222 could contain a diaphragm or bellows, an expansion 7 ' chamber could be added, and a filling fluid other than well fluid could be 8 used. Additional contouring of area could also be done to modify coupling 9 bandwidth and efficiency. Shaping of ports and arraying of multiple ports could also be done for the same purpose.
11 Directional coupling also could be obtained by using two or 12 more transducers of the invention as described with ports axially separated 13 to synthesize a phased array. The directional coupling would be achieved 14 by driving each transducer with a signal appropriately predistorted in phase and amplitude. Such active directional coupling can be achieved over a 16 . wider bandwidth than that achieved with a passive system. Of course, the 17 predistortion functions would have to account for all coupled resonances in 18 each particular situation.
19 THE COMMUNICATION SYSTEM: The communication system of the present invention will be described with reference to Figures 16 through 23.
21 - With reference to Figure 16, a borehole, generally referred to 22 by the reference numeral 1100, is illustrated extending through the earth 23 1102. Borehole 1100 is shown as a petroleum product completion hole for 24 illustrative purposes. It includes a casing schematically illustrated at DOCKET NO. 424-3666-CIP

1 and production tubing 1106 within which the desired oil or other petroleum 2 product flows. The annular space between the casing and production 3 tubing is filled with borehole completion liquid represented by dots 1108.
4 The properties of a completion fluid vary significantly from well to well and over time in any specific well. It typically will include suspended particles or 6 partially be a gel. It is non-Newtonian and may include non-linear elastic 7, properties. Its viscosity could be any viscosity within a wide range of 8 possible viscosities. Its density also could be of any value within a wide 9 range, and it may include corrosive solid or liquid components like a high density salt such as a sodium, calcium, potassium and/or a bromide 11 compound.
12 A carrier 1112 for a downhole acoustic transceiver (DAT) and 13 its associated transducer is provided on the lower end of the tubing 1106.
14 As illustrated, a transition section 1114 and one or more reflecting sections 1116, most desirably are included and separate carrier 1112 from the 16 remainder of production tubing 1106. Carrier 1112 includes numerous slots 17' in accordance with conventional practice, within one of which, slot 1118, the 18 communication transducer (DAT) of the invention is held by strapping or the 19 like. One- or more data gathering instruments or a battery pack also could be housed within slots like slot 1118. In the preferred embodiment, one slot 21 is utilized to house a battery pack, and another slot (slot 1118) is utilized to 22 house the transducer and associated electronics. It will be appreciated that 23 a plurality of slots could be provided to serve the function of slot 1118.
The 24 annular space between the casing and the production tubing is sealed adjacent the bottom of the borehole by packer 1110. The production tubing 26 1106 extends through the packer and a safety valve, data gathering 27 instrumentation, and other wellbore tools, may be included.
DOCKET NO. 424-3666-CIP

1 It is the completion liquid 1108 which acts as the transmission 2 medium for acoustic waves provided by the transducer. Communication 3 between the transducer and the annular space which confines such liquid 4 is represented in Figure 16 by port 1120. Data can be transmitted through the port 1 120 to the completion liquid via acoustic signals. Such 6 communication does not rely on flow of the completion liquid.
7 A surface acoustic transceiver (SAT) 1126 is provided at the 8 surface, communicating with the completion liquid in any convenient fashion, 9 but preferably utilizing a transducer in accordance with the present invention. The surface configuration of the production well is 11 diagrammatically represented and includes an end cap on casing 1104. The 12 production tubing 1106 extends through a seal represented at 1122 to a 13 production flow line 1123. A flow line for the completion fluid 1124 is also 14 illustrated, which extends to a conventional circulation system.
In its simplest form, the arrangement converts information 16 . laden data into an acoustic signal which is coupled to the borehole liquid at 17 one location in the borehole. The acoustic signal is received at a second 18 location in the borehole where the data is recovered. Alternatively, 19 commur ~ication occurs between both locations in a bidirectional fashion.
And as a further alternative, communication can occur between multiple 21 locations within the borehole such that a network of communication 22 transceivers are arrayed along the borehole. Moreover, commurncauon 23 could be through the fluid in the production tubing through the product 24 which is being ~ produced. Many of the aspects of the specfic communication method described are applicable as mentioned previously DOCKET NO. 424-3666-CIP

' ' -33-1 to communication through other transmission medium provided in a 2 borehole, such as in the walls of the tubing 1106.
3 Referring to Figure 17, the downhole acoustic transducer 4 (DAT) 1200' at the downhole location is coupled to a downhole acoustic transceiver (DAT) data acquisition system 1202 for acoustically transmitting 6 data collected from the DAT's associated sensors 1201. The downhole 7 acoustic transceiver (DAT) data acquisition system 1202 includes signal 8 processing circuitry, such as impedance matching circuits, amplifier circuits, 9 filter circuits, analog-to-digital conversion circuits, power supply circuits, and a microprocessor and associated circuitry. The DAT 1202 is capable of 11 both modulating an electrical signal used to stimulate the transducer 1200 12 for transmission, and of demodulating signals received by the transducer 13 1200 from the surface acoustic transceiver (SAT) 1204 data acquisition 14 system. The surface acoustic transceiver (SAT) data acquisition system 1204 includes signal processing circuitry, such as impedance matching 16 circuits, amplifier circuits, filter circuits, analog-to-digital conversion circuits, 17 power supply circuits, and a microprocessor and associated circuitry. In 18 other words, the DAT 1202 both receives and transmits information.
19 Similarly, the SAT 1204 both receives and transmits information. The communication is directly be;ween the DAT 1202 and the SAT 1204 through 21 transducers 1200, 1205. Alternatively, intermediary transceivers could be 22 positioned within the borehole to accomplish data relay. Additional DATs 23 could also be provided to transmit independently gathered data from their 24 own sensors to the SAT or to another DAT.
More specifically, the bi-directional communication system of 26 the invention establishes accurate data transfer by conducting a series of DOCKET NO. 424-3666-CIP

1 steps designed to characterize the borehole communication channel 1206, 2 choose the best center frequency based upon the channel characterization, 3 synchronize the SAT 1204 with the DAT 1202 , and, finally, bi-directionally 4 transfer data. This complex process is undertaken because the channel 1206 through which the acoustic signal must propagate is dynamic, and this 6 time variant. Furthermore, the channel is forced to be reciprocal: the 7 transducers are electrically loaded as necessary to provide for reciprocity.
8 In an effort to mitigate the effects of the channel interference 9 upon the information throughput, the inventive communication system characterizes the channel in the uphole direction 1210. To do so, the DAT
11 1202 sends a repetitive chirp signal which the SAT 1204, in conjunction with 12 its computer 1128, analyzes to determine the best center frequency for the 13 system to use for effective communication in the uphole direction.
14 Currently, the channel 1210 is characterized only in the uphole direction;
thus, an implicit assumption of reciprocity is incorporated into the design.
16 It will be recognized that the downhole direction 1208 could be 17 characterized rather than, or in addition to, characterization for uphole 18 communication. Moreover, in the current design, the bit rate of the data 19 transmitted by the DAT 1202 may be higher than the commands sent by the SAT 1204 to the DAT 1202. Thus, it is advantageous to achieve the best 21 signal to noise ratio for the uphole signals.
22 Alternatively, if reciprocity is not met, each transceiver could 23 be designed to characterize the channel in the incoming communication 24 direction: the SAT 1204 could analyze the channel for uphole communication 1210 and the DAT 1202 could analyze for downhole 26 communication 1208, and then command the corresponding transmitting DOCKET NO. 424-3666-CIP

1 system to use the best center frequency for the direction characterized by 2 it. However, this alternative would require extra processing capability in the 3 DAT 1202. Extra processing capability means greater power and size 4 requirements which are, in most instances, undesirable.
In addition to choosing a proper channel for transmission, 6 . system timing synchronization is important to any coherent communication 7 system. To accomplish the channel characterization and timing 8 synchronization processes together, the DAT begins transmitting repetitive 9 chirp sequences after a programmed time delay selected to be longer than the expected lowering time.
11 Figures 20A-C depict the signalling structure for the chirp 12 sequences. In a preferred implementation, a single chirp block is one 13 hundred milliseconds in duration and contains three cycles of one hundred 14 fifty (150) Hertz signal, four cycles of two hundred (200) Hertz signal, five 15. cycles of two hundred and fifty (250) Hertz signal, six cycles of three 16 hundred (300) Hertz signal, and seven cycles of three hundred and fifty 17 (350) Hertz cycles. The chirp signal structure is depicted in Figure 20A.
18 Thus, the entire bandwidth of the desired acoustic channel, one hundred 19 and fifty to three hundred and fifty (150-350) Hertz, is chirped by each block.
As depicted in Fgure 20B, the chirp block is repeated with a 21 time-delay between each block. As shown in Figure 20, this sequence is 22 repeated three times at two minute intervals. The first two sequences are 23 transmitted sequentially without any delay between them, then a delay is 24 created before a third sequence is transmitted. During most of the DOCKET NO. 424-3666-CIP

1 remainder of the interval, the DAT 1202 waits for a command (or default 2 tone) from the SAT 1204. The specific sequence of chirp signals 'should not 3 be construed as limiting the invention: variations on the basic scheme, 4 including but not limited to different chirp frequencies, chirp durations, chirp pulse separations, etc., are foreseeable. It is also contemplated that PN
6 sequences, an impulse, or any variable signal which occupies the desired 7 , spectrum could be used.
8 The SAT 1204 of the preferred embodiment of the invention 9 uses two microprocessors 1616, 1626 to effectively control the SAT
functions, as is illustrated in Figure 22. The host computer 1128 controls all 11 of the activities of the SAT 1204 and is connected thereto via one of two 12 serial channels of a Model 68000 microprocessor 1626 in the SAT 1204.
13 In alternative embodiments, the SAT 1204 may be mounted on an 14 input/output card which is adapted in size to be inserted within an expansion slot of a host computer. The 68000 microprocessor 16 . accomplishes the bulk of the signal processing functions that are discussed 17 below. The second serial channel of the 68000 microprocessor is 18 connected to a 68HC11 processor 1616 that controls the signal digitization, 19 the retrieval of received data, and the sending of tones and commands to the DAT. The chirp sequence is received from the DAT by the transducer 21 1205 and converted into an electrical signal from an acoustic signal. The 22 electrical signal is coupled to the receiver through transformer 1600 which 23 provides impedance matching. Amplifier 1602 increases the signal level, 24 and the bandpass filter 1604 limits the noise bandwidth to three hundred and fifty (350) Hertz centered at two hundred and fifty (250) Hertz and also 26 functions as an anti-alias filter. Of course, different or additional bandwidths 27 between as large- as one kilohertz to as small as one Hertz could be utilized DOCKET NO. 424-3666-CIP

FROiH :BHI PRTENT DEPT 713 739 8043 1994.08-16_ 17:44 #534 P.03/36 in alternative embodiments of the present invention, but for purposes of this 2 written description, the range of frequencies between one hundred Hertz 3 and three hundred Hertz will be discussed and utilized as an example, and 4 not as a limitation of the present invention.
Referring to Figure 21, the DAT 1202 has a single 68HC11 6 microprocessor 1512 that controls all transceiver functions, the data logging 7 ' activities, logged data 'retrieval and transmission, and power control.
For g simplicity, all communications are interrupt-driven. In addition, data from the g sensors are buffered, as represented by block 1510, as it arrives.
Moreover, the commands are processed in the background by algo~rrhms ~ 1 1700 which are specifically designed for that purpose.
12 The DAT 1202 and SAT 1204 include, though not explicitly 13 shown in the block diagrams of Fgures 21 and 22, all of the requisite 14 microprocessor support circuitry. These circuits, including RAM, ROM, clocks, and buffers, are well known in the art of microprocessor circuit 16 design.
Generation of the chirp sequence is accomplished by a digital 18 signal generator controlled by the DAT microprocessor 1572. Typically, the 19 chirp block is generated by a digital counter having its output controlled by a microprocessor to generate the complete chirp sequence. Circuits of this 21 nature are widely used for variable frequency dock signal generation. The 22 chirp generation circuitry is depicted as block 1500 in Figure 21, a .block 23 diagram of the DAT 1202. Note that the digital output is used to generate 24 .e three level signal at 7502 for driving the transducer 1200. It is chosen far this application to maintain most of the signal energy in the acoustic DOCKET NQ. 424-3666-CIP

_38_ 1 spectrum of interest: one hundred and fifty Hertz to three hundred and fifty 2 Hertz. The primary purpose of the third state is to terminate operation of 3 the transmitting portion of a transceiver during its receiving mode: it is, in 4 essence, a short circuit.
Figure 18 and Figure 19 are flow charts of the DAT and SAT
6 . operations, respectively. The chirp sequences are generated during step 7 ~ 1300. Prior to the first chirp pulse being transmitted after the selected time g delay, the surface transceiver awaits the arrival of the chirp sequences in g accordance with step 1400 in Figure 19. The DAT is programmed to transmit a burst of chirps every two minutes until it receives two tones: fc 11 and fc+ 1. Initial synchronization starts after a "characterize channel"
12 command is issued at the host computer. Upon receiving the "characterize 13 channel" command, the SAT starts digitizing transducer data. The raw 14 transducer data is conditioned through a chain of amplifiers, anti-aliasing filters, and level translators, before being digitized. One second data block 16 (1024 samples) is stored in a buffer and pipelined for subsequent 17 ~ processing.
1g The functions of the chirp correlator are threefold. First, it 19 synchronizes the SAT TX/RX clock to that of the DAT. Second, it calculates a clock error between the SAT and DAT tirnebases, and corrects the SAT
21 clock to match that of the DAT. Third, it calculates a one Hertz resolution 22 channel spectrum.
23 The correlator performs a FFT ('Fast Fourier Transform") on 24 a .25 second data block, and retains FFT signal bins between one hundred and forty Hertz to three hundred and sixty Hertz. The complex valued signal DOCKET NO. 424-3666-CIP

' , . _3g_ 1 is added coherently to a running sum buffer containing the FFT sum over 2 the last six seconds (24 FFTs). In addition, the FFT bins are incoherently 3 added as follows: magnitude squared, to a running sum over the last 6 4 seconds. An estimate of the signal to noise ratio (SNR) in each frequency bin is made by a ratio of the coherent bin power to an estimated noise bin g power. The noise power in each frequency bin is computed as the 7 difference of the incoherent bin power minus the coherent bin power. After g the SNR in each frequency bin is computed, an "SNR sum" is computed by g summing the individual bin SNRs. The SNR sum is added to the past twelve and eighteen second SNR sums to form a correlator output every .25 11 seconds and is stored in an eighteen second circular buffer. In addition, a ~ 2 phase angle in each frequency bin is calculated from the six second buffer 13 sum and placed into an eighteen second circular phase angle buffer for later 14 use in clock error calculations.
After the chirp correlator has run the required number of seconds of data through and stored the results in the correlator buffer, the 17 correlator peak is found by comparing each correlator point to a noise floor 1g plus a preset threshold. After detecting a chirp, all subsequent SAT
1g activities are synchronized to the time at which the peak was found.
2p After the chirp presence is detected, an estimate of sampling 21 clock difference between the SAT and DAT is computed using the eighteen 22 second circular phase angle buffer. Phase angle difference (~~) over a six second time interval is computed for each frequency bin. A first clock error 24 estimation is computed by averaging the weighted phase angle difference over all the frequency bins. Second and third clock error estimations are similarly calculated respectively over twelve and one hundred and eighty-five DOCKET NO. 424-3666-CIP

" ' -40-1 second time intervals. A weighted average of three clock error estimates 2 gives the final clock error value. At this point in time, the SAT clock is adjusted and further clock refinement is made at the next two minute chirp 4 interval in similar fashion.
After the second clock refinement, the SAT waits for the next 6. set of chirps at the two minute interval and averages twenty-four .25 second 7 chirps over the next six seconds. The averaged data is zero padded and g then FFT is computed to provide one Hertz resolution channel spectrum.
g The surface system looks for a suitable transmission frequency in the one 1p hundred and fifty Hertz to three hundred and fifty Hertz. Generally, a 11 frequency band having a good signal to noise ratio and bandwidths of 12 approximately two Hertz to forty Hertz is acceptable. A width of the 13 available channel defines the acceptable baud rate.
14 The second phase of the initial communication process 15. involves establishing an operational communication link between the SAT
16 1204 and the DAT 1202. Toward this end, two tones, each having a 17 duration of two seconds, are sequentially sent to the DAT 1202. One tone 1g is at the chosen center frequency and the other is offset from the center 19 frequency by exactly one hertz. i nis step in the operation of the SAT 1204 2p is represented by block 1406 in Figure 19.
21 The DAT is always looking for these two tones: fc and fc+ 1, 22 after ~t has stopped chirping. Before looking for these tones, it acquires a 23 one second block of data at a time when it is known that there is no signal.
24 The noise collection generally starts six seconds after the chirp ends to 25 provide time for echoes to die down, and continues for the next thirty DOCKET NO. 424-3666-CIP

1 seconds. During the thirty second noise collection interval, a power 2 spectrum of one second data block is added to a three second long running 3 average power spectrum as often as the processor can compute the 1024 4 point (one second) power spectrum.
The DAT starts looking for the two tones approximately thirty-g , six seconds after the end of the chirp and continues looking for them for a 7 period of tour seconds (tone duration) plus twice the maximum propagation g time. The DAT again calculates the power spectrum of one second blocks g as fast as it can, and computes signal to noise ratios for each one Hertz p wide frequency bins. All the frequency components which are a preset threshold above a noise floor are possible candidates. If a frequency is a 12 candidate in two successive blocks, then the tone is detected at its ~3 frequency. If the tones are not recognized, the DAT continues to chirp at 14 the next two minute interval. When the tones are received and properly recognized by the DAT, the DAT transmits the same two tones back to the g . _ SAT at the selected carrier frequency fc, which is recognized as an 17 ~ acknowledgement signal. Then, the SAT transmits characters to the DAT, ~g which causes the DAT to look for a coded "recognition sequence signal".
19 Control data follows the recognition signal. Preferably, the recognition 2p sequence signal includes a baud rate Signal which identifies to the DAT the . 21 expected baud rate, as determined by the SAT. The DAT will then respond 22 to any command provided to it after the recognition sequence signal.
Typically, the SAT will command the DAT to begin the transmission of data 24 frorn the downhole location for receipt by the SAT at the uphole location.
A by-product of the process of recognizing the tones is that it enables the DAT to synchronize its internal clock to the surface DOCKET NO. 424-3666-CIP

" ' -42-1 transceiver's clock. Using the SAT clock as the reference clock, the tone 2 pair can be said to begin at time t=0. Also assume that the clock in the 3 surface transceiver produces a tick every second as depicted in Figure 23.
This alignment is desirable to enable each clock to tick off seconds synchronously and maintain coherency for accurately demodulating the g data. However, the DAT is not sure when it will receive the pair, so it 7 ~ conducts an FFT every second relative to its own internal clock which can g be assumed not to be aligned with the surface clock. When the four g seconds of tone pair arrive, they will more than likely cover only three one 1p second FFT interval fully and only two of those will contain a single 11 frequency. Figure 23 is helpful in visualizing this arrangement. Note that 12 the FFT periods having a full one second of tone signal located within it will 13 produce a maximum FFT peak.
14 Once received, an FFT of each two second tone produces both amplitude and phase components of the signal. When the phase component of the first signal is compared with the phase component of the 17 second signal, the one second ticks of the downhole clock can be aligned 1g with the surface clock. For example, a two hundred Hertz tone followed 1g immediately by a two hundred and one Hertz tone is sent from the 2p transceiver at time t=0. Assume that the propagation delay is one and one-2~ half seconds and the difference between the one second ticking of the clocks is .25 seconds. This interval is equivalent to three hundred and fifty cycles of two hundred Hertz Hz signal and 351.75 cycles of two hundred 24 and 6ne Hertz tone. Since an even number of cycles has passed~for the 25 first tone, its phase will be zero after the FFT is accomplished. However, the phase of the second tone will be two hundred and seventy degrees from 27 that of the first tone. Consequently, the difference between the phases of DOCKET NO. 424-3666-CIP

1 each tone is two hundred and seventy degrees which corresponds to an 2 offset of .75 seconds between the clocks. If the DAT adjusts its clock by .75 seconds, the one second ticks will be aligned. In general, the phase 4 difference defines the time offset. This offset is corrected in this implementation. The timing correction process is represented by step 1308 6 in Figure 18 and is accomplished by the software in the DAT, as 7 represented by blocks 1504, 1506, 1508 in the DAT block diagram of Figure g 21.
It should be noted that the tones are generated in both the DAT and SAT in the same manner as the chirp signals were generated in 11 the DAT. As described previously, in the preferred embodiment of the 12 invention, a microprocessor controlled digital signal generator 1500, 1628 13 creates a pulse stream of any frequency in the band of interest.
14 Subsequent to generation, the tones are converted into a three level signal at 1502, 1630 for transmission by the transducer 1200, 1205 through the 16 ~ acoustic, channel.
17 After tone recognition and retransmission, the DAT adjusts its 1g clock, then switches to the Minimum Shift Keying (MSK) modulation 19 receiving mode. (Any modulation technique can be used, although it is 2p preferred that MSK be used for the invention for the reasons discussed 21 below.) Additionally, if the tones are properly recognized by the SAT as 22 being identical to the tones which were sent (step 1408), it transmits a MSK
23 modulated command instructing the DAT as to what baud rate the downhole 24 unit should use to send its data to achieve the best bit energy to noise ratio at the SAT (step 1410). The DAT is capable of selecting 2 to 40 baud in 2 baud increments for its transmissions. The communication link in the DOCKET NO. 424-3666-CIP

1 downhole direction is maintained at a two baud rate, which rate could be increased if desired. Additionally, the initial message instructs the downhole transceiver of the proper transmission center frequency to use for its 4 transmissions.
If, however, the tones are not received by the downhole 6 transceiver, it will revert to chirping again. SAT did not receive the two tone 7 , acknowledgement signal since DAT did not transmit them. In this case the 8 operator can either try sending tones however many times he wants to or g try recharacterizing channel which will essentially resynchronize the system.
In the case of -sending two tones again, SAT will wait until the next tone 11 transmit time during which the DAT would be listening for the tones.
12 , If the downhole transceiver receives the tones and retransmits 13 them, but the SAT does not detect them, the DAT will have switched to this 14 MSK mode to await the MSK commands, and it will not be possible for it to _ detect the tones which are transmitted a second time, if the operator 16 decides to retransmit rather than to recharacterize. Therefore, the DAT
will 17 wait a set duration. If the MSK command is not received during that period, 1 g it will switch back' to the synchronization mode and begin sending chirp 19 sequences every two minutes. This same recovery procedure will be Zp implemented if the established communication link should subsequently 21 deteriorate.
_ As previously mentioned, the commands are modulated in an 23 MSK format. MSK is a form of modulation which, in effect, is binary 24 frequency shift keying (FSK) having continuous phase during the frequency shift occurrences. As mentioned above, the choice of MSK modulation for DOCKET NO. 424-3666-CIP

1 use in the preferred embodiment of the invention should not be construed 2 as limiting the invention. For example, binary phase shift keying (BPSK), quadrature phase shift keying (~PSK), or any one of the many forms of 4 modulation could be used in this acoustic communication system.
In the preferred embodiment, the commands are generated by 6 , the host computer 1128 as digital words. Each command is encoded by a 7 cyclical redundancy code (CRC) to provide error detection and correction 8 capability. Thus, the basic command is expanded by the addition of the g error detection bits. The encoded command is sent to the MSK modulator portion of the 68HC11 microprocessor's software. The encoded command 11 bits control the same digital frequency generator 1628 used for tone 12 generation to generate the MSK modulated signals. In general, each 13 encoded command bit is mapped, in this implementation, onto a first 14 frequency and the next bit is mapped to a second frequency. For example, "rf the channel center frequency is two hundred and thirteen Hertz, the data 16 _ . may be mapped onto frequencies two hundred and eighteen Hertz, 17 representing a "1 ", and two hundred and eight Hertz, representing a "0".
1g The transitions between the two frequencies are phase continuous.
1g Upon receiving the baud rate command, the DAT will send an acknowledgement to the SAT. If an acknowledgement is not received by 21 the SAT, it will resend the baud rate command if the operator deades to 22 retry. If an operator wishes, the SAT can be commanded to resynchronize 23 and cecharacterize with the next set of chirps.
24 . A command is sent by the SAT to instruct the DAT to begin sending data. If an acknowledgement is not received, the operator can DOCKET NO. 424-3666-CIP

1 resend the command if desired. The SAT resets and awaits the chirp signals if the operator decides to resynchronize. However, if an 3 acknowledgement is sent from the DAT, data are automatically transmitted 4 by the DAT directly following the acknowledgement. Data are received by the SAT at the step represented at 1434.
g , Nominally, the downhole transceiver will transmit for four 7 minutes and then stop and listen for the next command from the SAT.
8 Once the command is received, the DAT will transmit another 4 minute 9 block of data. Alternatively, the transmission period can be programmed via the commands from the surface unit.
11 It is foreseeable that the data may be collected from the 12 sensors 1201 in the downhole package faster than they can be sent to the 13 surface. Therefore, as shown in Figure 21, the DAT may include buffer 14 memory 1510 to store the incoming data from the sensors 1201 for a short . duration prior to transmitting it to the surface.
1g The data is encoded and MSK modulated in the DAT in the 17 same manner that the commands were encoded and modulated in the SAT, 1g except the DAT may use a higher data rate: two to forty baud, for 1g transmission. The CRC encoding is accomplished by the microprocessor 1512 prior to modulating the signals using the same circu'~try 1500 used to 21 generate the chirp and tone bursts. The MSK modulated signals are 22 converted to tri-state signals 1502 and transmitted via the transducer 1200.
In both the DAT and the SAT, the digitized data are processed 24 by a quadrature demodulator. The sine and cosine waveforms generated DOCKET NO. 424-3666-CIP

' ' -47-1 by oscillators 1635, 1636 are centered at the center frequency originally chosen during the synchronization mode. Initially, the phase of each oscillator is synchronized to the phase of the incoming signal via carrier transmission. During data recovery, the phase of the incoming signal is tracked to maintain synchrony via a phase tracking system such as a g Costas loop or a squaring loop.
The I and Q channels each use finite impulse response (FIR) g low pass filters 1638 having a response which approximately matches the g bit rate. For the DAT, the filter response is fixed since the system always receives thirty-two bit commands. Conversely, the SAT receives data at 11 varying baud rates; therefore, the filters must be adaptive to match the 12 current baud rate. The filter response is changed each time the baud rate 13 is changed.
14 Subsequently, the I/Q sampling algorithm 1640 optimally _ samples both the I and Q channels at the apex of the demodulated bit.
16 However, optimal sampling requires an active clock tracking circuit, which 17 is provided. Any of the many traditional clock tracking circuits would suffice:
1g a tau-dither clock tracking loop, a delay-lock tracking loop, or the like.
The 19 output of the I/Q sampler is a stream of digital bits representative of the 2p information.
21 The information which was originally transmitted is recovered 22 by decoding the bit stream. To this end, a decoder 1642 which matches 23 the encoder used in the transmitter process: a CRC decoder, decodes and 24 detects errors in the received data. The decoded information carrying data is used to instruct the DAT to accomplish a new task, to instruct the SAT to DOCKET NO. 424-366E-CIP

1 receive a different baud rate, or is stored as received sensor data by the 2 SAT's host computer.
g The transducer, as the interface between the electronics and the transmission medium, is an important segment of the current invention;
therefore, it was discussed separately above. An identical transducer is 6 . used at each end of the communications link in this implementation, 7 although it is recognized that in many situations it may be desirable to use 8 differently configured transducers at the opposite ends of the 9 communication link. In this implementation, the system is assured when analyzing the channel that the link transmitter and receiver are reciprocal 11 and only the channel anomalies are analyzed. Moreover, to meet the 12 environmental demands of the borehole, the transducers must be extremely 13 rugged or reliability is compromised.
14 THE MEASUREMENT-WHILE-DRILLING APPLICATION: In the foregoing _ description, the transducer and communication system are described as 16 being used in a producing wellbore. However, the transducer and 17 communication system can also be utilized in a wellbore during completion 18 operations or drilling operations. Figure 24 shows one such utilization of the 1g transducer and communication system during drilling operations. As is shown, wellbore 601 extends from surface 603 to bottom hole 605.
21 Drillstring 607 is disposed therein, and is composed of a section of drill pipe 22 609 and a section of drill collar 611. The drill collar 611 is located at the 23 lowermost portion of drillstring 607, and terminates at its lowermost end at 24 rockbit 613. As is conventional, during drilling operations, fluid is circulated downward through drillstring 607 to cool and lubricate drillbit 613, and to 26 wash formation cuttings upward through annulus 615 of wellbore 601.
DOCKET NO. 424-3666-CIP

Typically, one of two types of drillbits are utilized for drilling 2 operations, including: (a) a rolling-cone type drillbit, which requires that 3 drillstring 607 be rotated at surface 603 to cause disintegration of the 4 formation at bottom hole 605, and (b) a drag bit which includes cutters which are disposed in a fixed position relative to the bit, and which is rotated 6 by rotation of drillstring 607 or by rotation of a portion of drill collar 7 through utilization of a motor.
g In either event, a fluid column exists within drillstring 607, and g a fluid column exists within annulus 615 which is between drillstring 607 and wellbore 601. It is common during conventional drilling operations to utilize 11 a measurement-while-drilling data transmission system which impresses a 12 series of either positive or negative pressure pulses upon the fluid within 13 annulus 615 to communicate data from drill collar section 611 to surface 14 603. Typically, a measurement-while-drilling data transmission system includes a plurality of instruments for measuring drilling conditions, such as 16 temperature and pressure, and formation conditions such as formation 17 . resistivity, formation gamma ray discharge, and formation dielectric 1g properties. It is conventional to utilize measurement-while-drilling systems 19 to provide to the operator at the surface information pertaining to the 2p progress of the drilling operations as well as information pertaining to 21 characteristics or qualities of the formations which have been traversed by 22 rockbit 613.
23 In Figure 24, measurement-while-drilling subassembly 617 24 includes sensors which detect information pertaining to drilling operations and surrounding formations, as well as the data processing and data DOCKET NO. 424-3666-CIP

1 transmission equipment necessary to coherently transmit data from drill 2 collar 611 to surface 603.
A great need exists in the drilling industry for additional 4 information; and in particular information which can be characterized as "near-drillbit" information. This is particularly true for drilling configurations 6 which utilize steering subassemblies, such as steering subassembly 621, 7 which allow for the drilling of directional wells. The utilization of steering g equipment ensures that the measurement-while-drilling data gathering and g transmission equipment is located thirty to sixty (30-60) feet from drill bit -613. Directional turns of drillbit 613 cannot be accurately monitored and 11 controlled utilizing the sensing and data transmission equipment of 12 measurement-while-drilling system 617; near drillbit information would be 13 , required in order to have a higher degree of control. Some examples of 14 desirable near drillbit data include: inclination of the lowermost portion of the drilling subassembly, the azimuth of the lowermost portion of the drilling 16 subassembly, drillbit temperature, mud motor or turbine rpm, natural gamma ray readings for freshly drilled formations near the bit, resistivity readings for 1g freshly drilled formations near the bit, the weight on the bit, and the torque 1 g on the bit.
2p In the present invention, measurement subassembly 619 is 21 located adjacent rockbit 613, and includes a plurality of conventional 22 instruments for measuring near drillbit data such as inclination, azimuth, bit 23 temperature, turbine rpm, gamma ray activity, formation resistivity, weight 24 on bit, and torque on bit, etc. This information may be digitized and multiplexed in a conventional fashion, and directed to acoustic transducer 26 623 which is located in an adjacent subassembly for transmission to DOCKET NO. 424-3666-CIP

~ -51 1 receiver 625, which is located upward within the string, and which is 2 adjacent measurement-while-drilling subassembly 617. In this configuration, 3 near-drillbit data may be transmitted a short distance (typically thirty to ninety feet) between transmitter 623 and receiver 625 which utilize the transducer of the present invention as well as the communication system of 6 the present invention.
7 The communication system of the present invention continually g monitors the fluid within annulus 615 with a characterization signal to identify g the optimum frequencies for communication, as was discussed above. The data may be routed from receiver 625 to measurement-while-drilling system 11 617 for storage, processing, and retransmission to surface 603 utilizing 12 conventional measurement-while-drilling data transmission technologies.
13 This provides an economical and robust data communication system for the 14 dynamic and noisy environment adjacent drill collar section 611, which allows communication of near-drillbit data for integration into a conventional 16 data stream from a measurement-while-drilling data communication system:
17 Alternatively, or additionally, transducer 627 may be provided 1g at surface 603 for receipt of acoustic data signals from either one or both 1g of transducer 623 or transducer 625. Or, alternatively, and more likely, 2p transducer 625 may be utilized to transmit to an intermediate transducer 21 located in the drillpipe section 609 of the drillstring 611 which will be able to 22 transmit a greater distance than transducers located in the drill collar section 23 611. _ In this manner, the transducers and communication system of the 24 present invention may be utilized as a data transmission system which is parallel with a conventional measurement-while-drilling data transmission 26 system. This is particularly useful, since conventional measurement-while-DOCKET NO. 424-3666-CIP

1 drilling systems require the continuous flow of fluid downward through 2 drillstring 607. During periods of noncirculation or if circulation is lost, 3 conventional measurement-while-drilling systems cannot communicate data from wellbore 601 to surface 603, since no fluid is flowing. The transducer and communication system of the present invention provide a redundant g system which can be utilized to transmit data to surface 603 during 7 quiescent periods when no fluid is being circulated within the wellbore.
This g ' provides considerable advantages since there are significant periods of time g during which data communication is not possible during drilling operations 1p utilizing conventional measurement-while-drilling technologies. In alternative 11 embodiments, the transducer and communication system of the present 12 invention can be utilized to completely replace a conventional measurement-13 while-drilling data transmission system, and provide a sole mechanism for 14 the communication of data and control systems within the wellbore during drilling operations.
1g THE GAS INFLUX DETECTION APPLICATION: The transducer and 17 communication system of the present invention can also be utilized during 1g drilling operations for the detection of the undesirable influx of high pressure 1g gas into the annulus of a wellbore. As is known to those skilled in the art, 2p the introduction of high pressure gas into the fluid column of a wellbore 21 during drilling operations can result in loss of control of the well, or even a 22 "blowout" in the most extreme situations. Considerable effort has been 23 expended to provide safety equipment at the wellhead which can be utilized 24 to prevent the total loss of control of a well. Once a drilling operator has determined that an influx of gas is likely to have occurred, remedial actions can be taken to lessen the impact of the gas influx. Such remedial actions 27 include increasing or decreasing circulation within the well, or increasing the DOCKET NO. 424-3666-C I P

_53_ 1 viscosity and density of the drilling fluid within the well. Finally, safety 2 equipment can be utilized to prevent total loss of control within a wellbore 3 due to a significant gas influx. The prior art technology is entirely 4 inadequate in providing sufficient data to the operator during drilling operations which would allow the operator to avoid the many problems 6 associated with gas influx. Fortunately, the transducer and communication 7 system of the present invention can be utilized in drilling operations to g ~ provide the operator with significant data pertaining to (1) whether an undesirable influx of gas has occurred, and (2) the location of the gas "bubble" once it has entered the drilling fluid column. It is important to note 11 that an influx usually occurs as an introduction of a fluid slug, which is the 12 gas in liquified form due to the high pressure exerted by the fluid column.
13 Since the gas generally has a lower density, it will rise within the fluid 14 column; as it rises, it will come out of solution, and take the form of a gas "bubble".
16 In accordance with the present invention, an influx of gas can 17 be detected in a fluid column within a wellbore which defines a 18 communication channel by performing the following steps:
1g (1) at least one actuator is provided in communication with the wellbore for conversion of at least one of (a) a provided coded electrical 21 signal to a corresponding generated coded acoustic signal during a 22 message transmission mode of operation, and (b) a provided coded 23 acoustic signal to a corresponding generated coded electrical signal during 24 a message reception mode of operation; preferably, only one actuator/transducer is provided, and this is located at the surface of the 26 wellbore at the wellhead, and is in fluid communication with the fluid column DOCKET NO. 424-3666-CIP

1 within the annulus of the wellbore, although in alternative embodiments one 2 or more transducers may be provided downhole within the drillstring;
3 (2) the transducer is utilized to generate an interrogating 4 signal at a' selected location within the wellbore; the characterizing signal may be a "chirp" which includes a plurality of signal components, each g having a different frequency, and spanning over a preselected range of 7 frequencies, or it may be an acoustic signal which includes only a single g frequency component;
g' (3) the transducer is utilized to apply the interrogating signal 1p to the communication channel which is defined, preferably, in the fluid column within the wellbore annulus;
12 (4) the interrogating signal is transmitted through the 13 communication channel and is received by either a different transducer, or 14 is echoed back upward through the communication channel and received by the transmitting transducer;
1g (5) next, the interrogating signal is analyzed to identify at 17 least one of the following: (a) portions of a preselected range of 1g frequencies which are suitable for communicating data in the wellbore;
these 1g portions may be identifiied by either frequency or bandwidth or both, or by 2p signal-to-noise characteristics such as a signal-to-noise ratio, or signal 21 amplitude; (b) communication channel attributes, such as communication 22 channel length, or communication channel impedance; (c) signal attributes, 23 such as signal amplitude, signal phase, and the occurrence of loss of the 24 signal;
DOCKET NO. 424-3666-CIP

' ~ -55-1 (6) Finally, the steps of utilizing, applying, receiving, and 2 analyzing are repeated periodically to identify changes in at least one of:
(a) 3 portions of the preselected range of frequencies which are suitable ' for 4 communicating data in the wellbore including frequency changes, bandwidth changes, changes in a signal-to-noise characteristic, changes in signal 6 amplitude of signals transmitted within the portion, and signal time delays 7 for signals transmitted within the portion, (b) communication channel g , attributes, including changes in communication channel length or g communication channel impedance, or (c) changes in signal attributes 1p (either interrogating signals or subsequent signals) including changes in 11 signal amplitude, changes in signal phase, loss of signal, or signal time 12 delay.
13 When a single transducer is utilized, in the preferred 74 embodiment of the present invention, such transducer should be located at 15 the surface, and should be utilized to transmit a signal downward within the 16 communication channel (of the annulus). Typically, the acoustic signal is reflected off of the drill collar portion of the drillstring, and thus travels back 1g upward through the communication channel where it is received by the 1g transducer which generated the signal. In fact, any signal provided by the 2p surface transducer gill travel a multiple number of times downward and then 21 upward within the communication channel as the signal repeatedly reflects 22 off of the drill collar portion of the drillstring. In one embodiment of the 23 present invention, one or more acoustic markers may be placed within the 24 drillstring at selected locations. Each member is generally larger in diameter 25 than the adjoining dritlstring, and provides a reflection surface at one or 26 more known distances. The reflection of acoustic signals off of these 27 markers is monitored for changes which indicate its presence of gas.
DOCKET NO. 424-3666-C1P

1 Figure 25 graphically depicts a laboratory test of the 2 transducer of the present invention in a wellbore five hundred (500) feet 3 deep. In this figure, the X-axis is representative of the acoustic travel path 4 in units of time, which have been normalized to units of length, and the Y-axis is representative of signal strength of the signal received by the 6 transducer which is disposed at the surface. Peak 70i is representative of 7 a signal which is generated by the surface acoustic transceiver. At the 8 ~ termination of time interval r o 3, the first echo 705 is detected by the surface 9 acoustic transceiver. During this time interval, the acoustic signal has traveled downward through the annulus, reflected from the drill collar, and 11 traveled back upward to the surface acoustic transceiver for reception. At 12 the termination of time interval 707, the second acoustic signal 709 is 13 received by the surface acoustic transceiver. At the termination of time 14 interval 711, the third acoustic echo 713 is received by the surface acoustic transceiver. At the termination of time interval 715, the fourth acoustic echo 16 717 is received by the'surface acoustic transceiver. At the termination of 17 time interval ~ ~ 9, the fifth echo ~ 2 ~ is received by the surface acoustic 18 ' ' ' transceiver. At the termination of time interval '7 2 3, the sixth echo ~ 2 5 is 19 detected by the surface acoustic transceiver. At the termination of time interval ~ 2 ~ the seventh echo ~ 2 9 is detected by the surface acoustic 21 transceiver.
22 Thus, it can be seen that if the annulus is unobstructed, a 23 regular pattern of echoes can be expected for acoustic signals emitted by 24 the surface acoustic transceiver. Each echo occurs at a predetermined time on a-time line, which corresponds to the distance between the surface 26 acoustic transceiver and the drill collar portion of the drillstring. Since the 27 length of the drillstring is known, and the frequency of transmission of the DOCKET NO. 424-3666-CIP ' ' . . _57_ acoustic signal is also known, the echoes occur as expected, unless an 2 obstruction exists within the annulus of the wellbore.
An influx of gas into the annulus can serve as an obstruction which will cause the occurrence of echoes to be shifted in time. This occurs, since the gas "slug" or "bubble" has different acoustic transmission g properties from the drilling mud, and will provide a boundary from which 7 reflection is expected. Thus, the generation of an acoustic signal by the g surface acoustic transceiver, and subsequent monitoring of the return g echoes, can be utilized to detect (1 ) the presence of a gas influx, and (2) the location of a gas influx. Assume for example that a gas bubble has entered the annulus during drilling operations, and is located at a position 12 midway between the surface acoustic transceiver and the drill collar. The expected result is an echo pattern which indicates a travel path of approximately one-half of that which was previously encountered during ~5 monitoring. The operator at the surface can analyze the echo pattern and 16 thus determine the presence and location of the gas bubble.
In addition to monitoring the length of the communication ~g channel, the transducer and communication system of the present invention may be utilized to detect the influx of gas by monitoring the extent of 2p amplitude attenuation in the echo signals as compared to amplitude 2~ attenuation during periods of operation during which no gas influx is present 22 within the communication channel; said monitoring is preferably not a 23 calibrated measurement but is instead a relative comparison of attenuation 24 and the description which follows utilizes the term "amplitude attenuation' in 25 this sense. With reference again to Figure 25, the presence of undesirable gas bubbles within the fluid column which comprises a communication DOCKET NO. 424-3666-CIP

1 channel will result in a change in acoustic impedance of the fluid column 2 and will result in additional reflection losses. This change in acoustic 3 impedance of the fluid column will result in a change in the amplitude 4 attenuation of the signal as it echoes within the wellbore by traveling downward and upward. For example, if a large amount of gas is present 6 within the communication channel, a greater or lesser degree of signal 7 attenuation may be observed than is normally encountered during periods g ~ of operation during which no gas is present within the communication g channel. Therefore, by continuously monitoring and comparing attenuation values, the transducer of the present invention can be utilized to detect 11 changes in acoustic impedance which occur due to the influx of gas within 12 the communication channel. Any detected change in communication 13 channel length or impedance can be considered to be detection of changes 14 in "communication channel attributes".
Signals which are transmitted from the transducer can be 16 monitored for changes in amplitude, or significant time delays, both of which 17 . could iridicate the presence of an undesirable gas influx. Additionally, 18 signals which have been transmitted by the transducer can be monitored for 19 signal phase shift, which in an acoustic transmission environment ~ corresponds to significant transmission delays (which are far greater than 21 one wavelength).
22 The transducer and communication system of the present 23 invention may also be utilized during a gas influx detection mode of 24 operation, wherein the process of selection of the one or more portions of available bandwidth for data communication is utilized to detect changes in 26 the communication channel which indicate that a gas influx has occurred.
DOCKET NO. 424-3666-CIP

_59_ 1 As is shown in Figure 26, surface acoustic transceiver 743 may be coupled 2 in a position at the surface to communicate with annulus fluid 741 within 3 wellbore 735. Drilling rig 731 is provided to rotate drillstring 733. As is 4 conventional, drillstring 733 includes an upper section of drill pipe 737 and a lower section of drill collar 739. Rockbit 738 disintegrates geologic 6 formations as drillstring 733 is rotated relative to wellbore 735.
7 During selected portions of the drilling operations, surface g acoustic transceiver 743 (and associated personal computer monitor 745) g is utilized to transmit interrogating signals downward into wellbore 735 1p through annulus fluid 741, which is the communication channel. One or 11 more reflection markers may be provided and coupled in position within drill 12 pipe section 737 of drillstring 733. Alternatively, the reflective boundary 13 provided by drill collar 739 may be utilized as a reflection surface.
Surface 14 acoustic transceiver 743 transmits either (a) a signal which includes a 15 number of signal components, each having a different frequency, spanning 16 a preselected frequency range, or (b) transmits a signal having a fixed 17 frequency. The signal is propagated downward through annulus fluid 741, 1g and reflects off of drill collar 739, and returns toward the surface for 19 reception by surface acoustic transceiver 743.
2p If a signal is transmitted which includes a number of different 21 frequency components, the surface acoustic transceiver can analyze the 22 signal-to-noise attributes of various frequency portions over the preselected 23 frequency range to identify one or more optimal bands within the frequency 24 range, typically each being approximately ten (10) Hertz wide, which are 25 optimal at that time for the communication of data within wellbore 735. The 26 particular optimal bands may be identified by upper and lower frequencies, DOCKET NO. 424-3666-CIP

' . , -60-1 or a center frequency and a bandwidth. In either characterization, a specific 2 portion of a frequency range is identified as being preferable to other 9 portions of the frequency range for the efficient transmission of data.
4 ' The introduction of an undesirable gas influx into the annulus fluid 741 within wellbore 735 will alter the acoustic impedance of the annulus 6 fluid 741, and thus will alter the optimal frequency portions for data 7 transmission. Data can be obtained by continually characterizing the 8 communication channel of annulus fluid 741 during periods in which no gas 9 influx is present within annulus fluid 741. Subsequent characterizations of annulus fluid 741 can be compared to the historical data to ident'rfy changes 11 in the optimal bandpass portions of the preselected frequency range to 12 identify the occurrence of a gas influx.
13 In Figure 26, rockbit 738 is depicted as traversing a high 14 pressure gas zone 747. This causes a gas influx 749 to enter annulus fluid 741. Typically, gas influx 749 will enter annulus fluid 741 as a "slug" of fluid.
16 As it rises, it will come out of solution and become a gas "bubble". The 17 presence of either the fluid slug or the gas bubble should cause a significant 18 change in the optimal operating frequencies for the communication channel 19 of annulus fluid 741. These abrupt changes in the optimal data transmission frequencies should provide an indication to the operator at the surface that 21 an undesirable gas influx has occurred.
22 In alternative embodiments, one or more transducers may be 23 located within drillstring 733 for the transmission and/or reception of 24 acoustic signals. For example, downhole acoustic transceiver 740 may be provided in a position adjacent drill collar 739 for the receipt or transmission DOCKET NO. 424-3666-CIP

1 of acoustic signals. In this configuration, downhole acoustic transceiver 2 may be utilized, as was described above in connection with the description 3 of the data communication system, to generate a characterizing signal which 4 is detected by surface acoustic transceiver 743, and processed by PC
monitor 745, also as was described above. Surface acoustic transceiver 8 743 and downhole acoustic transceiver 740 may be utilized to transmit 7 signals back and forth across the communication channel of annulus fluid 8~ 741. Changes in the communication channel, changes in signals 9 transmitted between surface acoustic transceiver 74~ and downhole acoustic transceiver 740, as well as changes in the optimal communication 11 frequencies can be utilized to detect the entry of an undesirable gas influx 12 749. Echoes which are generated within the communication channel of 13 annulus.fluid 741 which originate from either the surface acoustic transceiver i4 743 or the downhole acoustic transceiver 740 can be util'~zed to pinpoint the location and size of a gas bubble as it travels upward within the annulus of 16 ~ the wellbore:
17~ ~ '~ ' The present invention can be utilized to monitor gas influx into 18 a well during drilling, and detect the event prior to the influx bubble reaching 19 the surface. This will greatly improve safety, by preventing blowout of the well or other serious loss of control situations. The system can be ud'lized 21 to defect the position of the top of the bubble. Since the transducer and 22 communication system of the present invention does not require that 23 circulation be present within the wellbore, the present invention can be 24 uG'lized to detect the influx of gas during quiescent periods during which no fluid is being circulated within the wellbore, such as tripping and casing 26 , operations: The present invention also allows for the detection of small gas 27 bubbles, far earlier than is capable under conventional techniques. The DOCKET NO. 424-3666-CIP

' ' -62-1 present invention also allows for significant changes to occur in the well 2 during drilling operations, such as changes in mud weight, and the 3 subtraction or addition of drillstring sections, since the system allows for 4 continuous monitoring of the communication channel to determine optimum operating frequencies. This feature allows for the automatic and continuous 6 adjustment of the "baseline" performance during significant reconfigurations 7 of the wellbore, without requiring any significant knowledge by the operator 8 of acoustic systems. In short, altered acoustic paths, disrupted acoustic 9 returns, disrupted frequency channels, and changes in the time of flight as well as changes in amplitude relative to previous amplitudes can be utilized 11 separately or together to identify the occurrence of an undesirable gas 12 influx, and once the influx has been detected, can be utilized to pinpoint the 13 location, and perhaps size, of the gas influx.
14 ALTERNATIVE DATA COMMUNICATION SYSTEM: As an alternative to identifying specific and narrow portions of a frequency band which provide 16 optimal data transmission, the communication system of the present 17 invention can utilize an opposite approach which utilizes a very broad band 18 in its entirety to transmit a corresponding binary character, such as a binary 19 one, and which uses another broad band to identify a corresponding binary character, such as a binary zero. It has been shown by Drumheller, in an 21 article entitled "Acoustical Properties of Drillstrings", Sandia National 22 Laboratories, Paper No. SAND88-0502, published in August of 1988, that 23 acoustical signals of specific frequencies travel from the bottom of a 24 drillstring to the surface with only small attenuation. These frequencies are contained within frequency bands. Within these frequency bands there can 26 be wide variation of the attenuation of any one particular frequency, but 27 some or most of the frequencies within the band pass through the drillstring DOCKET NO. 424-3666-CIP

1 notwithstanding dramatic changes in the wellbore environment. Thus, 2 selecting one particular frequency band as the modulation frequency for a data transmission system ensures that there is only a small probability that 4 all frequencies within the band will be attenuated and lost.
In accordance with the present invention, the communication 6 channel is in the wellbore, either a fluid column or a tubular member, is 7 , analyzed to determine an optimal frequency band which may be utilized to 8 designate a particular binary value, such as a binary "one", while another g separate frequency band is identified to represent the opposite binary character, such as a binary "zero". For example, the communication 11 channel is investigated to identify a broad frequency band, such as five 12 hundred ninety Hertz to six hundred and ninety Hertz (590-G90) which 13 corresponds to a binary "one", while it also investigated for a separate 14 frequency band, such as eight hundred and twenty Hertz to nine hundred and twenty Hertz (820-920) which corresponds to a binary "zero'.
16 . The transducers of the present invention are utilized to 17 generate an acoustical signal which includes a plurality of signal portions, 18 each portion representing a different frequency within the band, the portions 19 altogether spanning the entire width of the selected frequency band. For , example, for the binary one, the acoustic transducer will produce a signal 21 which includes a plurality of signal components spread across the five 22 hundred ninety to six hundred ninety (590-690) bandwidth. Likewise, for the 23 binary "zero", the transducer will generate an acoustical signal which 24 includes a plurality of signal components which span the range of frequencies between eight hundred and twenty Hertz and nine hundred and 26 twenty Hertz (820-920).
DOCKET NO. 424-3666-CIP

1 During a reception mode of operation, the transducer, and 2 associated microprocessor computer, is utilized to analyze the energy levels 3 of acoustic signals detected in the separate frequency band ranges.
4 Preferably, the energy of the zero band is compared to a baseline noise level which , has previously been obtained for the range of frequencies.
g Likewise, the energy level of the frequency range representative of the 7 , binary "zero" is compared with a baseline energy level previously acquired g for the same frequency r ange.
g These concepts are illustrated in block diagram form in Fgures 27 and 28, with figure 27 depicting the logic associated with the transmitter, 11 and Figure 28 depicting the logic associated with the receiver.
12 Referring first to Figure 27, sensor data is provided by sensors 13 801 to microprocessor 805 and digital storage memory 803. When 14 transmission of the data is desired, microprocessor 805 actuates digital-to-_ analog converter 807 which generates an actuation signal for binary "ones', 16 and an actuation signal for binary "zeroes". Power driver 809 generates a 17 unique power signal associated with each binary zero, and a unique power 18 signal associated with each binary one, as is depicted in graph 811, with a 19 first preselected range of frequencies representing a binary "one", and a second preselected range of frequencies representing a binary "zero". In 21 the example of Figure 27, frequencies in the range of five hundred ninety to 22 six hundred and ninety Hertz (590-690) are representative of the binary 23 "one",-while frequencies in the range of eight hundred and twenty to nine 24 hundred and twenty Hertz (820-920) are representative of the binary "zero'.
This driving signal is supplied to transducer 813 which is acoustically DOCKET NO. 424-36fi6-CIP

1 coupled to the communication channel, which is preferably, but not necessarily, a fluid column within the wellbore.
3 The acoustic signal is conducted td a remotely located 4 transceiver, such as transducer 815 of Figure 28. The received acoustic signals are amplified at amplifier 817, and supplied simultaneously to g bandpass filter 819 and bandpass filter 829. In the example of Figures 27 7 , and 28, bandpass filter 819 is a bandpass filter which allows for the passage g of frequencies in the range of five hundred ninety to six hundred and ninety g (590-690) Hertz, while bandpass filter 829 allows for the passage of frequencies in the range of eight hundred and twenty Hertz to nine hundred and twenty Hertz (820-920). The outputs of bandpass fitters 819, 829 are ~2 supplied to subsequent signal processing blocks.
13 More specifically, the output of bandpass filter 819 is supplied ~4 to integrator 821 which provides as an output an indication of the energy content of the signals in the range of frequencies corresponding to the binary "one". Likewise, the output of bandpass filter 829 is supplied to 17 integrator 831 which provides as an output an indication of the energy 1g contained by the signals in the range of frequencies corresponding to the 1g binary "zero". Base band integrator 823 is utilized to provide an indication 2p of the energy level contained within the range of frequencies corresponding 2~ to the binary "one" during periods which no signal is present. Likewise, 22 base band integrator 833 is utilized to provide as an output an indication of the energy contained within the frequency band corresponding to the binary 24 "zero" during periods of inactivity. As is shown in Figure 28, the output of 25 integrator 821 and base band integrator 823 is supplied to summing DOCKET NO. 424-3666-CIP

1 amplifier 825. Likewise, the output of integrator 831 and base band 2 integrator 833 are supplied to summing amplifier 835.
The output of summing amplifiers 825, 835 are provided to a comparator. If the output of summing amplifier 825 exceeds the output of summing amplifier 835, then the output of comparator 827 is a binary "one";
g however, if the output of summing amplifier 835 is greater than the output 7 of summing amplifier 825, then the output of comparator 827 is a binary g "zero". In this manner, the binary data provided as an output from g microprocessor 805 (of Figure 27) may be reconstructed at the output of comparator 827 in a remotely located transceiver.
11 Of course, in the present invention, the transducer which is 12 described herein may be utilized as an acoustic signal generator.
13 Furthermore, the data communication system described herein may be ~4 utilized to select the best range of frequencies for representing the binary "one" and the binary "zero".
DOCKET NO. 424-3666-CtP

Claims (27)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of detecting influx of gas into a fluid column in a wellbore therein which defines a communication channel, comprising:
providing at least one actuator for conversion of at least one of (a) a provided coded electrical signal to a corresponding generated coded acoustic signal during a message transmission mode of operation, and (b) a provided coded acoustic signal to a corresponding generated coded electrical signal during a message reception mode of operation;
utilizing said at least one actuator for generating an interrogating signal at a selected location within said wellbore;
applying said interrogating signal to said communication channel;
receiving said interrogating signal with said at least one actuator;
analyzing said interrogating signal to identify at least one of:
(a) portions of a preselected range of frequencies which are suitable for communicating data in said wellbore at that particular time;
(b) communication channel attributes; and (c) signal attributes;
repeating said steps of utilizing, applying, receiving, and analyzing to identify changes in at least one of:
(a) portions of said preselected range of frequencies which are suitable for communicating data in said wellbore;
(b) communication channel attributes; and (c) signal attributes;
which, correspond to a likely influx of gas into said fluid column in said wellbore.

2. A method according to claim 1:
wherein said portions of said preselected range of frequencies which are suitable for communicating data in said wellbore are identified by at least one of (a) frequency, (b) bandwidth, (c) a signal-to-noise characteristic, (d) signal amplitude, and (e) signal time delay.

3. A method according to claim 1:
wherein said communication channel attributes include at least one of:
(a) communication channel length; and (b) communication channel impedance.

4. A method according to claim 1:
wherein said signal attributes include at least one of:
(a) signal amplitude;
(b) signal phase;
(c) loss of signal in the selected portion of the preselected range of frequencies of the communication channel; and (d) signal time delay.

5. A method according to claim 1:
wherein said at least one actuator comprises a single actuator; and wherein said interrogating signal received by said single actuator is an echo signal in said communication channel.

6. A method according to claim 1:
wherein said at least one actuator comprises a first actuator disposed at a first wellbore location and a second actuator disposed at a second wellbore location;
and wherein said interrogating signal is transmitted between said first and second actuators.

7. A method according to claim 1, further comprising:
providing a reflection marker and coupling it to a wellbore tubular; and reflecting said interrogating signal off of said reflection marker.

8. A method of detecting at least one of (a) a fluid influx and (b) a gas influx into a fluid column in a wellbore therein which defines a communication channel, comprising:
providing at least one actuator for conversion of at least one of (a) a provided coded electrical signal to a corresponding generated coded acoustic signal during a message transmission mode of operation, and (b) a provided coded acoustic signal to a corresponding generated coded electrical signal during a message reception mode of operation;
utilizing said at least one actuator for generating an interrogating signal at a selected location within said wellbore;
applying said interrogating signal to said communication channel;
receiving said interrogating signal with said at least one actuator;
analyzing said interrogating signal to identify at least one of:
(a) portions of a preselected range of frequencies which are suitable for communicating data in said wellbore at that particular time;
(b) communication channel attributes; and (c) signal attributes;

repeating said steps of utilizing, applying, receiving, and analyzing to identify changes in at least one of:
(a) portions of said preselected range of frequencies which are suitable for communicating data in said wellbore;
(b) communication channel attributes; and (c) signal attributes;
which, correspond to a likely occurrence of at least one of (a) fluid influx and (b) gas influx into said fluid column in said wellbore.

9. A method according to claim 8:
wherein said portions of said preselected range of frequencies which are suitable for communicating data in said wellbore are identified by at least one of (a) frequency, (b) band width, (c) a signal-to-noise characteristic, (d) signal amplitude, and (e) signal time delay.

10. A method according to claim 8:
wherein said communication channel attributes include at least one of:
(a) communication channel length;
(b) communication channel impedance;
(c) frequency band width; and (d) phase shift.

11. A method according to claim 8:
wherein said signal attributes include at least one of:
(a) signal amplitude;
(b) signal phase;
(c) loss of signal;
(d) signal time delay;
(e) frequency response; and (f) acoustic spectral density.

12. A method according to claim 8:

wherein said at least one actuator comprises a single actuator; and wherein said interrogating signal received by said single actuator is an echo signal in said communication channel.

13. A method according to claim 8:
wherein said at least one actuator comprises a first actuator disposed at a first wellbore location and a second actuator disposed at a second wellbore location;
and wherein said interrogating signal is transmitted between said first and second actuators.

14. A method according to claim 8, further comprising:
providing a reflection marker and coupling it to a wellbore tubular; and reflecting said interrogating signal off of said reflection marker.

15. A method of detecting at least one of (a) fluid influx, and (b) gas influx into a fluid column in a wellbore therein which defines a communication channel, comprising:
providing at least one actuator for conversion of at least one of (a) a provided coded electrical signal to a corresponding generated coded acoustic signal during a message transmission mode of operation, and (b) a provided coded acoustic signal to a corresponding generated coded electrical signal during a message reception mode of operation;
utilizing said at least one actuator for generating an interrogating signal at a selected-location within said wellbore;
applying said interrogating signal to said communication channel;

receiving said interrogating signal with said at least one actuator;
analyzing said interrogating signal to identify at least one of:
(a) portions of a preselected range of frequencies which are suitable for communicating data in said wellbore at that particular time;
(b) communication channel attributes; and (c) signal attributes;
repeating said steps of utilizing, applying, receiving, and analyzing to identify changes in at least one of (a) portions of said preselected range of frequencies which are suitable for communicating data in said wellbore;
(b) communication channel attributes; and (c) signal attributes;
which, correspond to at least one of a likely (a) fluid influx, and (b) gas influx, into said fluid column in said wellbore; and displaying information which is sufficient to allow a human operator to detect and monitor at least one of a likely (a) fluid influx, and (b) gas influx.

16. A method according to claim 15:
wherein said portions of said preselected range of frequencies which are suitable for communicating data in said wellbore are identified by at least one of (a) frequency, (b) band width, (c) a signal-to-noise characteristic, (d) signal amplitude, and (e) signal time delay.

17. A method according to claim 15 wherein during said step of displaying, at least one of the following communication channel attributes is displayed:
(a) communication channel length;

(b) communication channel impedance;
(c) frequency band width; and (d) phase shift .

18. A method according to claim 15 wherein during said step of displaying, at least one of the following signal attributes is displayed:
(a) signal amplitude;
(b) signal phase;
(c) loss of signal;
(d) signal time delay;
(e) frequency response; and (f) acoustic spectral density.

19. A method according to claim 15:
wherein said at least one actuator comprises a single actuator; and wherein said interrogating signal received by said single actuator is an echo signal in said communication channel.

20. A method according to claim 15:
wherein said at least one actuator comprises a first actuator disposed at a first wellbore location and a second actuator disposed at a second wellbore location;
and wherein said interrogating signal is transmitted between said first and second actuators.

21. A method according to claim 15, further comprising:
providing a reflection marker and coupling it to a wellbore tubular; and reflecting said interrogating signal off of said reflection marker.

22. A method of detecting an influx into a wellbore utilizing a communication channel in said wellbore, comprising:
(a) providing at least one actuator for conversion of at least one of (1) a provided coded electrical signal to a corresponding generated coded acoustic signal during a message transmission mode of operation, and (2) a provided coded acoustic signal to a corresponding generated coded electrical signal during a message reception mode of operation;
(b) generating an interrogating signal at a selected location within said wellbore;
(c) applying said interrogating signal to said communication channel;
(d) receiving said interrogating signal with said actuator;
(e) analyzing said interrogating signal to identify at least one of:
(1) communication channel attributes; and (2) signal attributes;
(e) repeating said steps of generating, applying, receiving, and analyzing to identify changes in at least one of:
(1) communication channel attributes; and (2) signal attributes; which correspond to an influx in said wellbore.

23. A method according to claim 22:
wherein said communication channel attributes include at least one of:
(1) communication channel length; and (2) communication channel impedance.

24. A method according to claim 22:
wherein said signal attributes include at least one of (1) signal amplitude;
(2) signal phase;
(3) loss of signal; and (3) signal time delay.

25. An apparatus for detecting an influx into a wellbore utilizing a communication channel, comprising:
(a) a signal generator for generating an interrogating signal at a selected location within said wellbore and applying said interrogating signal to said communication channel;
(b) a signal receiver for receiving said interrogating signal, said signal receiver comprising an actuator for conversion of at least one of (a) a provided coded electrical signal to a corresponding generated coded acoustic signal during a message transmission mode of operation, and (b) a provided coded acoustic signal to a corresponding generated coded electrical signal during a message reception mode of operation;
(c) an analyzer for analyzing said interrogating signal to identify at least one of:
(1) communication channel attributes; and (2) signal attributes;
(d) a processor for repeating said steps of generating, applying, receiving, and analyzing to identify changes in at least one of:
(1) communication channel attributes; and (2) signal attributes; which correspond to a n influx in said wellbore.

26. An apparatus according to claim 25:
wherein said communication channel attributes include at least one of:
(1) communication channel length; and (2) communication channel impedance.

27. An apparatus according to claim 25:
wherein said signal attributes include at least one of:
(1) signal amplitude;
(2) signal phase;
(3) loss of signal; and (4) signal time delay.