US 2714930 A
Description (OCR text may contain errors)
C. A. CARPENTER APPARATUS FOR PREVENTING PARAFFIN DEPOSITION Aug. 9, 1955 Filed Deo. 8, 1950 United States Patent() APPARATUS FR PREVENTING PARAFFIN DEPOSITION Clayton A. Carpenter, Wilmington, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application December 8, 1950, Serial No. 199,813
2 Claims. (Cl. 166-60) This invention relates generally to apparatus for electrically heating a flowing oil stream within a well bore. More particularly, this invention relates to an apparatus for electrically heating an upper portion of the column of oil flowing within the tubing of a flowing oil well.
Numerous methods have been employed in the prior art for heating oil wells such as by electrical means, heat transfer agents and the like. A considerable number of such inventions pertain to preventing paraffin deposition in the well bore equipment. In general, the employment of such methods and apparatus necessitates a general shutdown or killing of the well. Killing the well is highly undesirable since during the interval in which oil flow is shut in, the water in the flowing oil Within the formation becomes rather firmly attached to the formation in the vicinity thereby causing water logging and other difficulties.
The apparatus of this invention permits a flowing well to be fitted with heating equipment without any necessity whatsoever for shutting-in the well. Since it has been found that deposition of paraffin in the Well bore equipment is serious only in about the uppermost 1,000 feet or so of the equipment, the apparatus of this invention is specifically designed for heating only the uppermost portion of the fiowing oil column thereby conserving electrical energy.
It is therefore an object of this invention to heat a flowing oil column within the tubing from the earth surface to a short distance therebelow, for example 1,000 feet.
It is another object of this invention to provide an electrical resistance apparatus for heating an oil column within the tubing of the well bore whereby there is obtained a maximum transfer of heat to the flowing oil.
It is another object of this invention to provide an apparatus which is readily insertable into the tubing of a fiowing oil well without necessity of killing the well.
It is another object of this invention to employ a single cable to support a combination electrical contact to the tubing and weighting member and also to provide a resistance in the electrical circuit for the generation and transmission of thermal energy.
Other objects and advantages of this invention Will become apparent to those skilled in the art as the description thereof proceeds.
Briefly, this invention relates to a new apparatus for preventing paraffin deposition in the tubing of a well bore wherein only the upper portion of the tubing is subjected to heating. Such apparatus comprises a weight suspended within the upper part of the tubing on a cornbination supporting cable and resistance wire. Attached to the weight, or in the vicinity thereof, is a contacting device for electrically contacting the inner surface of the tubing. The weight and wire are inserted into the top of the tubing through any suitable sealing member for passing solid objects and wire into the tubing under seal. Such sealing means may be a system of resilient rubber seals having a center opening which is expandible under force to permit entry of the object while maintaining a pressure seal. The sealing means also provides electrical insulation between the body of the tubing and the resistance cable where the latter is not covered with electrical insulation. The electrical circuit for the resistance cable is provided by attaching a current source to the resistance cable whence the current flows through the wire to the contacting member in the vicinity of the weighting member, thence to the tubing whence it flows upwardly through the tubing to a grounded connection or other conductor and returns to the current source.
It is a particularly advantageous feature of the apparatus of this invention in that it employs a minimum of bulky equipment and lends itself to ready installation in the conventional flowing well. Furthermore, the insertion of the Weighting member, the contacting member, and the resistance cable through a sealing means eliminates any requirement of shutting-in the well during the installation.
Figure l shows a partial cross-sectional elevation view of the installation of the apparatus of this invention positioned Within a well bore.
Figure 2 shows the combination of a weighting member, a contacting member, and resistance cable such as is employed in Figure l.
Figure 3 shows a cross-sectional View of the resistance cable such as may be taken through the plane 3 3 of Figure 2, for example.
Figure 4 shows an alternative modification of the weighting member and contacting member.
Figure 5 shows a cross-sectional view of the weighting member-contacting member modication shown in Figure 4 taken through a plane 5 5.
Figure 6 shows one modification of packing glandA member 28 of Figure l, which is adaptable for inserting the resistance cable and other members therethrough while maintaining a pressure seal between the upper and lower faces of the packing gland.
Figure 7 shows a modification of the invention for inserting parts of the apparatus of this invention into a high pressure well wherein the Well is not killed during the inserting.
Referring now to Figure l, well casing 11 extends downwardly from the earths surface 12 into bore hole 13 to the vicinity of the upper boundary of oil-bearing sand 14. Well casing 11 is capped with tubing head 15. Tubing 16 is suspended through the tubing head 15 downwardly within casing 11. Tubing 16 terminates at its lower end in opening 17 which permits oil from oil pool 18 to flow into the tubing and force its way under pressure through the tubing to production line 19 whence it is withdrawn. Gas production separating from oil pool 18 flows upwardly in the annular zone created by the well casing 11 and tubing 16 to the vicinity of earth surface 12 whence it is withdrawn through gas production line 20.
In Figure 1 weighting member 25, contacting member 26 and resistance cable 27 are insertable through packing gland member 28 without necessity of killing the Well.
At the earth surface, current source 30 passes electrical energy to transformer 31 whose secondary winding has been tapped at a series of points. The one terminal of the secondary winding of transformer 31 is connected through conductor 32 to resistance cable 27 at its upper end. Resistance cable 27 is supported by suitable means not shown, Contact 33 is adapted to be connected in sequence to the series of tapped windings of transformer 31 and passes electrical energy therefrom through conductor r'ce 34 to a ground connection on tubing head 15 which is in turny electrically grounded to tubing 16.
Electrical energy from source 30 is thusly transmittable to resistance cable 27. Resistance cable 27 is electrically connected to contacting member 26 which in turn is electrically connected to tubing 16 by slidable contact therewith. A return path for the electrical energy to source 30 is thereby provided.
Referring now more particularly to Figure 2, resistance cable 27 is electrically connected to stationary sleeve 40 by suitable means not shown. Stationary sleeve is rigidly attached to weighting member 42 by securing member 41. Attached to stationary sleeve 40 are two or more radially extending spring contacting bows 43 and 44. Such bows comprise uninsulated electrical conductors, e. g., bare metal bow springs. The lower ends of bows 43 and 44 are in turn anchored to slidable sleeve 45 which is free to slide coaxially over the outer surface of Weighting member 42. The construction of bows 43 and 44 is such that their natural tension tends to pull slidable sleeve 45 upwardly toward stationary sleeve 40 with the resultant increase in the bowing of members 43 and 44.
In the arrangement described in Figure 2 it is apparent that the normal tendency of bows 43 and 44 when confined within a tubing of suitable relative dimension is to fill the confines of the zone of confinement and expand their outer section to touch the circumscribing tubing face. Accordingly, slidable sleeve 45 `moves upwardly and downwardly as the requirements of bows 43 and 44 change in accordance with changes in the diameter of the circumscribing environment.
Referring now to Figure 3, which shows a modiiication of the resistance cable 27 taken through the plane 3-3 of Figure 2, the central core of the resistance cable is preferably a steel strand or core of suitable dimensions and characteristics to support the weighting member which may be in the range of 200 to 1000 lbs. A plurality of conductors 51, for example copper wires, is stranded around, wound on, or supported by steel core 50. Preferably copper conductors 51 are wrapped in doublestranded glass or other electrical insulation. Conductors 51 are so constructed as to resist the flow of electricity therethrough, thereby generating heat which is transmitted to the surrounding oil. In the preferred modification, conductors 51 are wrapped with suitable high temperature electrical insulation which permits transmission of heat therethrough and protects cable 27 from electrically contacting tubing 16 and thereby short-circuiting resistance cable 27.
It is apparent that numerous modifications of electrical contacting means of the type employed in the petroleum lndustry, in electric logging operations and the like may be employed as contacting member 26. One alternative modification of such means comprises a series of spines which are curved to permit theirentry into a circumscribing member of small diameter and which expand as the diameter of the circumscribing member is increased and contract as the diameter is decreased.
Referring now to Figure 4, weighting member is supported by and electrically connected to resistance cable 61. Electrically and rigidly attached to weighting member 60 is sleeve 62 which in turn mounts flexible spines 63 and 64. Flexible spines 63, 64 and others not shown, expand to the inner wall of the tubing and make electrical contact therewith during variations in the level of weighting member 60.
Referring now to Figure 5, which carries the same numerical reference characters as Figure 4 and is a crosssectional view through plane S-S of Figure 4, weighting member 60 is surrounded by electrically connected rigid sleeve 62 to which are attached electrically conducting iiexible spines 63, 64, 65 and 66, respectively. The flexible spines push outwardly against circumscribing tubing 67 and make electrical contact therewith.
Referring now more particularly to Figure 6, tubing 16 of Figure 1 may be tted with a packing gland to permit entry of the resistance wire, etc. In Figure 6 packing gland 28 is fitted with a suitable retainer which holds resilient packing 71 in place. The center of packing 71 is equipped with a small expandible opening 72 through which the equipment including the weighting member, the contacting means, and the resistance cable are inserted. The expandible opening 72 is normally closed and seals the pressure within tubing 16. When the equipment is inserted, packing gland 28 forms a tight seal about it so that there is little pressure loss therethrough.
Referring now more particularly to Figure 7, the equipment may be inserted into the tubing through a specially created sealing zone. Tubing 80, which corresponds to tubing 16 of Figure l, is capped with a gate type control valve 81. Fitting 82 is screwed into valve 8l and sealing member S3 threads into fitting 82, In using this modiiication, the sealing member is fitted with a packing gland S5 through which the resistance cable is passed and which maintains a pressure seal. While the sealing member is detached from fitting 82, the contacting means and weighting assembly are squeezed into place, as shown, by compressing bows 43 and 44. With the apparatus in place within sealing member 83, the latter is attached to fitting 82 above closed gate valve 81. When sealing member 83 is secured, gate valve 81 is opened and the resistance cable is payed out by suitable means not shown to lower the contacting means and weighting member to the desired level. The arrangement is then employed in substantially the same manner as was described in connection with Figure l.
The electrically resistant cable may suitably comprise about 1000 feet of No. 10 copper wire covered with a double glass wrap of electrical insulation wound about a steel core of suitable dimensions for supporting a 500 pound sinker bar or weighting member. The weighting member is fitted with an electrical contacting mechanism of the type shown in Figure l and Figure 2. About volts of electrical potential is supplied to cross the resistance cable and the tubing. There is a current ow of about 91 amperes with the result that about 10 kilowatts of electrical power are converted to thermal energy. The generation of thermal power at this rate is sufficient to prevent parain deposition in a flowing well producing barrels of oil per day when the average ground level temperature is in the vicinity of 70 F.
In the application of this invention it is preferable to use alternating current inasmuch as such current is readily stepped up or down according to the changing requirements of the system. Thus alternating currents ranging from 50 to 2000 volts, and which have frequencies in the range of 25 to 400 cycles per second may be employed. When direct current is employed, it is preferable to employ voltages in the range of about 50 to 1000 volts.
The size and electrical properties of the stranded copper wire or other resistance cable should be such that the major portion, such as at least 50% and preferably 90% of the generation of thermal energy occurs within the resistance cable. Accordingly, it is desirable to use relatively large copper wire in order to maintain a high current flow therethrough. Under these conditions the thermal energy is to a large extent generated in the resistance cable.
The sinker bar or weighting means employed in this 'invention may be of any suitable shape or configuration and performs the task of weighting the resistance cable. The weighting assembly in general performs three functions, viz. it provides a tension on the cable so that it is drawn taut, it provides support for the contacting mechanism which contacts the tubing, and it serves to center the resistance cable in the bore hole, particularly at its lower end, and minimizes wear and tear on the cable during raising and lowering.
It should also be noted that by the method of 'this invention .the slack or tension created by expansion and contraction of the resistance cable arising from temperature fluctuations is continuously compensated for by the raising and lowering of the weighting member which maintains a constant tension on the cable.
With regard to the amount of heat generated in the resistance cable, such amount is generally determined by the characteristics of the oil being produced and the characteristics of the formation and the locale of the oil lield. Generally speaking, a temperature drop of only a few degrees Fahrenheit in the uppermost few thousand feet of tubing is suicient to cause an excessive accumulation of parain during continued operation of the well. In some cases the temperature of the formation is in the range of about 80 F. while the temperature in the oil pool may be in the range of about 70 F. and the atmospheric temperature around the well head may be as low as' 10 or 20 F. Under this type of situation it has been found preferable to supply an amount of heat to the oil in the last 500 or 1000 feet of ow which is sufcient to maintain the temperature in the range of about 70 F. and preferably not less than about 65 F.
Generally speaking, crude oil may flow from the formation at a given temperature T1 and will cool as it ows through relatively cooler formations toward the earth surface due to evaporation of gases, heat transfer with the cooler surrounding earth strata in the upper layers, etc.
With wax bearing oils and particularly with the limited class of oils described hereinafter, a wax and/or resin deposition begins when the oil cools below to a temperature T2 which is lower than T1. Progressive cooling below temperature T2 results in progressive deposits of wax and/ or resin. The oil flow generally reaches temperature T2 only during the uppermost 1000 or so of the well tubing. The heating of the oil flow by the process of this invention is so controlled that a temperature greater than the wax or resin deposition temperature T2 is maintained throughout the owing oil column and especially in the uppermost section of the flowing oil column.
Oils which are prone to deposit wax, resins, etc., upon cooling have been found to be identifiable by their physical properties. The deposition is a function of the amount and the gravity of the residuum obtained after a Bureau of Mines Hempel distillation as described in The Analytical Distillation of Petroleum and its Products, U. S. Bur. Mines Bull. 207, pp. 4-19 (1922). It has been found that oils for which the value of the expression Per cent residuum A. P. I. gravity of residuum is less than 2.0, particularly less than 1.5, are prone to deposit solids.
The tendency of an oil to deposit solids determined by the value of the expression:
(Cloud point in F of key fraction 2) (A. P. I. Gr. of the residuum) Per cent residuum is greater than 30, particularly greater than 50, are prone to deposit solids.
The method and apparatus of the present invention effects beneficial results in dealing with oils which are prone to deposit solids as determined by either of the above methods.
Where the heat radiation from the tubing and oil flow therethrough is non-uniform with respect to distance near the earth surface, the resistance cable may be so constructed that its electrical resistance is non-uniform and varies with respect to its length in order to vary the generation of thermal energy per unit distance so as to provide a constant temperature of the oil column owing therethrough independently of the level.
The foregoing disclosure of this invention is not to be considered as limiting since many variations may be made by those skilled in the art without departing from the spirit and scope of the following claims.
1. In combination, an electrically conductive well tubing positioned within a well; a cable extending within said tubing and supporting at its lower end an electrically conductive weighting member adapted to be lowered into and withdrawn from said tubing, said cable being substantially uniformly electrically resistant throughout its length and being maintained taut by the action of gravity on said weighting member; an electrically conductive upper sleeve rigidly attached to said weighting member; an electrically conductive lower sleeve free to slide along said weighting member; a plurality of electrically conductive radially extending spring bows disposed radially around said weighting member and attached at their upper ends to said upper sleeve and at their lower ends to said lower sleeve, said bows being adapted to frictionally engage the inner walls of said tubing; and means for applying an electric potential between said cable and said tubing.
2. In combination, an electrically conductive well tubing positioned within a well; a cable extending within said tubing and supporting at its lower end an electrically conductive weighting member adapted to be lowered into and withdrawn from said tubing, said cable comprising a center weight-supporting core, a substantially uniformly electrically resistant winding supported on the outer surface of said core, and means for electrically insulating said winding from said core, and said cable being maintained taut within said tubing by the force of gravity acting on said weighting member; a contacting member borne by said weighting member and adapted to provide electrical contact between said weighting member and said tubing; and means for applying an electrical potential between said cable and said tubing.
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