US2964941A - Method for determining production characteristics of pumping wells producing oil andbrine - Google Patents

Description

Dec. 20, 1960 e. A. MARSH AL 2,964,941 ON CHARACTERISTICS OF PRODUCING OIL AND BRINE METHOD FOR DETERMINING PRODUCTI PUMPING WELLS 2 Sheets-Sheet 1 Filed Dec; 12, 1955 STRIP CHART RECORD IN V EN TOR. GLENN A. MARSH HENRY L. CHAMBERLAIN ATTORNEY RESISTANCE OHMS Dec. 20, 1960 Filed Dec.

A MARSH ET AL METHOD FOR DETERMINING PRODUCTION CHARACTERISTICS OF PUMPING WELLS PRODUCING OIL AND 12, 1955 |-ONE CYCLE INITIAL CURVE, NORMAL STEADY PUMPING loNE IMMEDIATELY CYCLE AFTER STARTING UP, 2 ;A TER AFTER 5 MIN. SHUTDOWN ONE- CYC LE BRINE 2 Sheets-Sheet 2 5 MIN. AFTER STARTUP STARTUP TIME (ONE CYCLE=3V2 SECONDS) FIG. 5

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INVEN TOR. GLENN A. MARSH HENRY L. CHAMBERLAIN ATTORNEY Unite States atentO METHOD FOR DETERMINING PRODUCTION CHARACTERISTICS OF PUMPING WELLS PRODUCING OIL AND BRINE Glenn A. Marsh, Crystal Lake, and Henry L. Chamberlain, Olney, Ill., assignors to The Pure Oil Company, Chicago, 11]., a corporation of Ohio Filed Dec. 12, 1955, Ser. No. 552,485

2 Claims. (Cl. 73-155) This invention relates to a method for determining the characteristics of a liquid-producing well in which plunger pumps are employed to artificially stimulate and sustain the drainage of the liquid from a liquid-containing formation traversed by a well bore.

In the initial exploitation of fluid-producing subterranean reservoirs, the liquid is expelled from the reservoir into a well and lifted to the surface by means of the natural latent energy of the reservoir fluid. Once the reservoir pressure has depreciated to the point Where the well is no longer free-flowing, it is necessary to resort to artificial expedients for developing energy to lift the liquid from the reservoir to the surface. Although alternative methods are available, a large percentage of modern producing wells utilize rod-actuated plunger pumps for lifting the oil from the wells. The conventional plunger pump consists of a stationary assembly which is suspended from the wellhead on a column of tubing of suflicient length to immerse the stationary assembly in the well fluid. A traveling assembly cooperates with the stationary assembly and is given a reciprocating motion by a string of sucker rods which extends up through the tubing to the surface where it is interconnected to the end of a power-actuated walking beam or other mechanism capable of imparting an-up-and-down motion to the traveling assembly. By means of several valves positioned in the stationary assembly and the traveling assembly, which cooperate with one another, oil is drawn into the stationary assembly and lifted toward the surface through the tubing on each up-stroke of a plunger which forms a part of the traveling assembly. A wide variety of plunger pump designs is available; however, they all have the aforementioned features in common.

If an oil well being pumped in this manner produces a mixture which has electrical conductivity, it has been found that the electrical resistance characteristics of the fluid are cyclically modified in a manner which permits the analysis of a number of characteristics of the pumping well. It is, therefore, a primary objective of this invention to determine production characteristics of a pumping well, in which the liquid flow is being induced by a rod actuated plunger pump, by measuring quantitatively the fluctuations in resistance across electrodes installed in the flow lines of the pumping well and in contact with the flowing liquid. Another object of this invention is to correlate the resistance fluctuations with the corrosivity of the well fluid. An additional object of the invention is to utilize the cyclic fluctuations in resistance as a means for logging the production history of the well. These and other objects will be made more apparent from the following detailed description of the subject invention.

Figure l is a diagrammatic drawing showing a con ventional arrangement of pumping apparatus employing a rod-actuated plunger pump for lifting the oil from a. subterranean reservoir, and illustrating the disposition of test electrodes in the flow lines for measuring the elec trical characteristics of the flowing oil. Shown schcmat-- ically is the auxiliary equipment necessary for graphically metering these characteristics.

Figure 2 is a fragmentary view setting forth in detail a preferred method for installing the test electrodes in the flow lines of the conduit system.

Figure 3 is a cross sectional view of Figure 2 through line 3-3.

Figure 4 is a schematic diagram of an electrical detecting and measuring network which is interconnected to the electrode system installed in the flow line.

Figure 5 is a graphic presentation of the cyclic fluctuations showing typical resistance-time curves obtained by measuring the electrical resistance of flowing fluids in several different wells.

According to the instant invention, it has been found that the electrical resistance characteristics of a liquid lifted from a well by means of a rod-actuated plunger pump may be used as a criterion for determining the production characteristics of a well fluid having electrical conductivity. The electrical resistance characteristics are quantitatively measured in a facile manner by simply installing electrodes in the flow lines of a producing well and determining the resistance Values by conventional resistance measuring apparatus. in resistance thus produced, when graphically presented,

. can be used to determine the production characteristics l of a producing well, as a means for recording the production history of the producing well, in weighing a well in Which a dynamometer measurement is made to determine the load on the sucker rod as a function of position in the pumping cycle and others, as well as other applications apparent to those who are skilled in this particular art.

Reference to the drawing will facilitate an understanding of the instant invention. In Figure 1 is seen a complete installation of conventional equipment for pumping a well by means of a rod-actuated plunger-dis-- placement pump. In this exemplary well, a plurality of casing sections 10 is installed in the well bore. The wellhead is capped with a conventional casing head 11 from which is suspended a plurality of lengths of tubing 12 extending to adjacent the liquid-containing reservoir which is being produced. Positioned on the terminal extremity of this tubing is the sub-surface pumping equipment 13 briefly described above, which is immersed in the well liquid. Operating the pump mechanism 13 is the sucker rod which is connected to the plunger mechanism of the pump and extends up through the tubing to the surface, where it is connected to the pumping unit. In this illustrative arrangement, a conventional walking beam 15 is employed to impart the necessary reciprocating action to the string of sucker rods. At one end of this walking beam is mounted a horsehead 16 to which is connected the sucker rod 17 by means of wire lines 17a which hang along the face of the horsehead. Employing a conventional cross head 18, the walking beam, of which only a fragmentary section is shown, is pivotally mounted in a standard 19 and interconnected to a suitable prime mover, such as an internal combustion engine, electric motor, steam engine, etc., by a suitable coupling means so as to impart an eccentric movement to the walking beam. The casing head 11 is fitted with a suitable stufling box 20 in which a polished sucker rod 17 is installed. The casing head is also fitted with suitable flow lines 21 and 22 for withdrawing the produced well fluids. Mounted in flow lines 21 and 22 is a T-shaped fitting 23 in which electrodes 24 and 25 are installed. These electrodes 24 and 25 are electrically insulated from the flow lines in any suitable manner and are positioned within the flow lines so that they are in constant contact with the produced liquids. The electrodes are con-;

The cyclic fluctuations nected by leads 26 and 27 to a suitable measuring and detecting network 28 whereby the electrical resistance between the electrodes is recorded as a function of time. The illustrated external circuit in its simplest form comprises a battery 29, a variable resistance 30, and a milliammeter 31 serially interconnected with electrodes 24 and 25. A conventional strip chart recorder 32 is connected acros the variable resistance 30 by means of leads 33 and 34 and emplovs the IR drop produced in this circuit element as the signal input to produce visible manifestations of the cyclic fluctuations in resistance of the fluid flowing past and in contact with electrodes 24 and 25. Varying of the fluid composition in the flow line causes the electrodes to give a characteristic cyclic fluctuation for each pump stroke for a given set of well conditions.

The electrodes, which are shown schematically in Figure i, may be installed in the flow line in a variety of ways, depending upon the needs of the installation designer. A suggested expedient is shown in Figures 2 and 3, illustrating an installation which may be either permanent or temporary. A standard bull-plug 35, selected for proper mating with T-shaped fitting 23, is provided with openings 36 and 37 through which leads 26 and 27 pass. These leads are electrically connected to electrodes 24 and 25 such as by soldering, etc. The electrodes are inserted into the bull-plug cavity and held in a spaced relationship while the cavity is filled with a spacer material 38, e.g. vinyl resin, polymeric styrene, shellac. polyethylene, rubber, etc., having insulating properties. Although more complex designs may be employed, a simple electrode holder of this nature will suffice for most test work. Accordingly, this suggested installation is non-limiting and illustrative and only serves to exemplify this aspect of the subiect invention, as it is evident that other designs and modifications for installing the electrodes in the flow lines in direct and constant contact with the flowing well-produced liquids will be obvious to those skilled in the art. The electrodes are installed in the electrode holder in a close-spaced relationship employing a spacing which is small enough to get a good definition between the components of the heterogeneous flow system in contact with the electrodes.

Typical electrodes are steel rods, 1 /2 inches long, A inch in diameter, and spaced /4 inch apart. However, any electrode length, diameter, cross sectional configuration and spacing that will allow the electrodes to be conveniently installed in the flow line as a single unit are satisfactory. Also, solid electrical conductors other than steel can be used to fabricate the electrodes. While the use of two electrodes (insulated from each other and from the flow line) is preferred and may be necessary where flow lines constructed from non-metallic, nonelectrically conductive materials are employed, the use of a single insulated electrode is satisfactory in installations using metallic flow lines, since the line itself is used as the other electrode.

The electrodes installed in the flow lines of the pumping equipment are interconnected to a measuring and indicating network whereby a graphic presentation of the cyclic fluctuations in resistance is recorded. In the illustrated embodiment shown in Figure l, resistance measurements were made employing an RCA Volt Ohmyst. This apparatus was modified by placing a 40 ohm resistance in series with the meter coil and employing the modified apparatus as an ohmmeter. This modivolts for full scale deflection, a chart speed of 2 inches per minute, and a 1.0 second full scale balancing time. A constant potential of 1.53 volts was applied across the electrodes by the Volt Ohmyst. Other expedients may be employed to record and present the cyclical fluctuations in resistance in a manner depending upon the application of the resistance changes. For example, in Figure 4 is shown an integrating network which will produce a reading approximately proportional to the integrated resistance value. This type of analogue computer is utilized when the cyclic fluctuations are employed to analyze the corrosivity of the producing fluid by comparison of produced curves with a standard curve which serves as a criterion.

The potential across R will depend on the resistance across the electrodes. As this resistance fluctuates, the capacitor C tends to act as a sink by storing electrons when the potential is high, and releasing them when the potential is low. The potential recorded by the recorder R, which has the same characteristics as the above described recorder, is therefore related to the average resistance across the electrodes.

Other comparison measuring techniques which may be employed include a variety of A.C. or D.C. bridge measuring circuits in which the electrodes are installed in the bridge as one arm thereof. These resistance measurement techniques are only illustrative and serve to show simple expedients for obtaining and recording the resistance measurements. Other suitable techniques to efiectuate this objective will also be obvious to those skilled 'in the prior art.

The electrical potential impressed across the electrodes in studying the cyclic changes in electrical conductivity of the flowing well fluid depends upon spacing of the electrodes, resistance of the fluid, internal resistance of the detecting and measuring network, etc. Generally, circuit measurements employ 1-45 volts; however, con- 'ditions may arise which utilize potentials outside this range.

To illustrate the instant invention in its application to: production studies of wells, electrodes consisting of two parallel steel rods inch in diameter and 1 /2 inch long,

spaced 4 inch apart, and mounted in an electrode holder, were installed in the flow lines of an oil well located in Illinois, the well being artificially produced by means of a rod-actuated plunger pump. The fluid being produced was a brine-containing, crude petroleum oil.

' The electrodes were connected to a detecting and recordfication had a negligible efiect on the accuracy as the ing network consisting of a Volt Ohmyst-recorder combination as hereinbefore described.

A study of this well was being made to determine sucker rod stresses and adjust operating conditions to secure most eflicient pump performance employing the so-called dynamometer testing technique such as that described in Petroleum Production Engineering, Exploitation, Uren, 3rd ed., McGraw-Hill, pages 297-303. Prior to conducting the test phase of the study, a graphical presentation of the cyclic fluctuations in resistance of the flowing well fluid was obtained for the well. This is shown in Figure 5. The pumping apparatus was stopped and the dynamometer test equipment installed. The pump was then re-started. To insure that proper flow conditions existed, the resistance characteristics of the produced fluid were observed until the cyclic fluctuations obtained agreed and coincided with the original cyclic fluctuations in resistance obtained at the outset of the test. When such conditions again existed, the dynamometer test was continued. Typical graphical presentatons of the cyclic fluctuations obtained under steady pumping for flow conditions prevailing at the time the tests were made are shown in Figure 5. In Figure 5, the pattern of resistance versus time reverted quickly to the normal steady state pattern when the pump was started after a 5-minute shutdown. However, 'in other wells tested, the pattern did not return -to 'thenormal' steady state pattern for several hours. It is to be noted that one complete cycle is used in the comparative study. This cycle may be initiated at any phase in the reciprocative motion of the plunger rod, and is completed at the recurrent point of the same phase in the regular sequence of pumping operations.

It is intended that the foregoing examples be only illustrative and not limit the scope f the instant invention. Although the subject invention finds particular application in dynamometer testing of pumping equipment for determining sucker rod stresses and adjusting operating conditions to secure most eflficient pump performance, it may also be used in a compilation of the production history of a producing well. In this service, the characteristic cyclic fluctuations in resistance provide a criterion whereby it can be determined when the produced fluid composition is similar to the composition of a fluid produced at some previous time in the wells history. Also, other uses of this invention will be apparent to those skilled in this art.

From the illustrative example it is seen that this invention is directed primarily to studies of the characteristics of brine-containing crude petroleum oils. Fluids of this nature flow in a heterogeneous dynamic fluid system which is especially productive of the cyclic fluctuations in resistance. The system used here is applicable in wells producing between about 1 percent and 99 percent Water and between about 99 percent and 1 percent oil (by volume). The salt content of the water is immaterial.

It is thus seen that a novel method has been developed whereby the characteristics of a fluid produced from a well bore by means of a rod-actuated plunger pump crn be determined and/or analyzed. The method has application in a number of various types of well studies to be made in a rapid and accurate manner not heretofore practicable.

Accord ngly, we claim as our invention:

1. The method of obtaining a comparison of the liquid comprising water and oil being produced from a well by plunger-displacement pumping equipment at diflferent times comprising obtaining the cyclical fluctuation in electrical resistances of said liquid during at least one complete pumping cycle at each of said times thereby enabling a comparison thereof.

2. The method of dynamometer-testing the rod stress of a plunger-displacement pump during operation in a brine-petroleum producing well comprising, obtaining the cyclical fluctuation of electrical resistance of said brinepetroleum during at least one pumping cycle when the well is in normal production, thereafter installing the dynamometer testing equipment and obtaining the rod stress during at least one pumping cycle simultaneously with the cyclical fluctuation of electrical resistance when such cyclical fluctuation is the same as that of the well when in normal production.

References Cited in the file of this patent UNITED STATES PATENTS 1,089,030 Angell Mar. 3, 1914 1,739,724 Lake Dec. 17, 1929 2,289,687 Stuart July 14, 1942 2,360,742 Toth et a1. Oct. 17, 1944

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