GB2325332A - Power cable supported in coiled tubing by swelled elastomer - Google Patents

Abstract

A power 11 cable for an electrical submersible well pump is encased within metal coiled tubing 13. The coiled tubing 13 supports the weight of the power cable 11 as well as the downhole pump and motor. Electrical insulated conductors 17 having an extruded jacket 26 over them are inserted into the coiled tubing 13. A clearance exists between the outer diameter of the jacket 26 and the inner diameter 15 of the coiled tubing 13. A hydrocarbon liquid is pumped through this clearance causing one of the components of the electrical cable to swell into tight gripping contact with the coiled tubing 13. The electrical conductors 17 are twisted into a tight helix prior to having the jacket 26 extruding over them. Compliant layers 21 surround each insulated conductor. The compliant layers 21 and the twist allow radial movement of the conductors 17 relative to the jacket 26 when the coiled tubing 13 is being coiled onto a reel. Flow paths within the annular clearance are provided to assure that the hydrocarbon liquid reaches the full length of the coiled tubing 13 even though one of the components of the electrical cable will be undergoing swelling.

Description

POWER CABLE SUPPORTED IN COILED TUBING BY SWELLED ELASTOMER This invention relates in general to power cable for electrical submersible well pumps and in particular to an electrical cable installed within a string of coiled metal tubing.

Conventional electrical submersible well pumps for oil and deep water wells are supported on a string of production tubing. The production tubing comprises sections of steel pipe screwed together, each section being about thirty feet in length. The pump is a centrifugal pump driven by an AC motor located below the pump. A power cable extends from the surface alongside the tubing for supplying power to the motor. The power cable is strapped to the tubing at frequent intervals to support the weight of the power cable.

One disadvantage of the conventional pump assembly described above is that when the pump must be pulled for repair or replacement, the procedure is expensive. The operator needs a workover rig with the capability of pulling the sections of tubing. Pumps of this nature must be pulled typically at least every eighteen months.

Considering the cost of the workover rig as well as the down time for the well, the periodic expense is significant.

A few installations have been made employing coiled tubing. Coiled tubing is a continuous string of metal tubing which is brought to the wellsite on a large reel.

The coiled tubing unit unreels the tubing and forces it into the well. Coiled tubing has been used for various purposes in the past, and recently used to suspend electrical submersible pumps. An advantage of a coiled tubing supported pump is that it does not need a workover rig to pull it. Also, pulling and replacing it should be faster than production tubing.

One proposal in the past was to produce production fluid from the pump through the coiled tubing and strap the cable to the exterior of the coiled tubing. A disadvantage of this assembly is that a separate reel is needed for the power cable. Securing the straps would slow down the installation and pulling procedure.

Furthermore, commercially available coiled tubing is not large enough in diameter for desired production in many cases.

Some installations have been made with the electrical cable installed within the coiled tubing.

Production fluid from the pump flows through a casing surrounding the coiled tubing. The electrical cable is a three-phase cable having fairly large metal conductors.

The weight of the cable is such that it will not support itself in a deep well. Even if inserted within coiled tubing, the weight of the electrical cable needs to be supported by the coiled tubing. In one type of installation, separate mechanical anchors are spaced along the length of the insulated electrical cable. The cable is inserted into the coiled tubing with the anchors retracted. The anchors are then shifted to a weight supporting position, gripping the inner diameter of the coiled tubing. U.S. Patent 5,435,351, Head, July 25, 1995, describes such a system.

Another proposal shown in U.S. Patent 5,191,173, Sizer et al, March 2, 1993, suggests using an elastomeric jacket of a type that will swell when exposed to a hydrocarbon liquid. The jacket is extruded over the insulated conductors during manufacturing. The jacketed electrical cable is then inserted into the coiled tubing. Then liquid hydrocarbon is pumped into the annular space surrounding the jacket, causing it to swell to frictionally grip the coiled tubing. Although the swelling is not instantaneous, it can occur rapidly enough to block the annular clearance before the hydrocarbon is able to completely flow through the annular space within several thousand feet of coiled tubing. The Sizer et al patent, identified above, shows various embodiments to avoid the jacket from swelling so as to block the flow of the hydrocarbon before the hydrocarbon reaches the end of the coiled tubing. These suggestions include the use of metal'strips and placing holes in the coiled tubing itself. Another difficulty encountered in inserting electrical cable inside coiled tubing occurs due to the large number of turns of the coiled tubing on the storage reel prior to deployment.

The radius from the axis of the reel to the centerline of each turn of the coiled tubing will not be the same as to the centerline of each turn of the electrical cable because of some deformation of the elastomer occurring during winding. As a result, if the electrical cable had the same length as the coiled tubing when straight, once wound, the electrical cable would be shorter. The Head patent, identified above, teaches to place waves or slack in the electrical cable between each of the anchors. As a result, the coiled tubing must be considerably larger in inner diameter than the outer diameter of the electrical cable.

In this invention, several embodiments are shown for overcoming the disadvantages discussed above. In one embodiment, a jacket is extruded around a bundle of electrical cable. The jacket is of an elastomer that swells upon application of a hydrocarbon fluid. The jacket has grooves that extend along its exterior throughout its length. The grooves provide flow channels for the hydrocarbon fluid so as to prevent blockage of the annular clearance before the hydrocarbon fluid reaches the entire length of the cable.

In another embodiment, the jacket is enclosed within a sheath which is of an elastomer that will not swell upon application of hydrocarbon fluid. The sheath has apertures spaced along its length which expose the jacket to the annular clearance. The hydrocarbon fluid flows through the apertures into contact with the jacket, causing it to swell. The sheath has longitudinal grooves on its exterior. Even though the sheath will stretch as a result of the swelling of the jacket, the grooves prevent complete closure of the annular clearance.

In two other embodiments, the jacket is made of an elastomer that does not swell upon the application of hydraulic fluid. In one of these embodiments, a gripping member is installed within a groove on the exterior of the jacket. The gripping member is a longitudinal strip of an elastomer that does swell upon application of hydraulic fluid. The gripping member extends circumferentially around the jacket only a fraction of the full circumferential length of the annular clearance. When completely swelled into gripping contact with the inner diameter of the coiled tubing, clearances will still remain for the passage of the hydrocarbon fluid.

In the other embodiment involving a nonswelling elastomeric jacket, the gripping member comprises solid cylindrical rods of an elastomer that are helically twisted about the three insulated conductors. The jacket is extruded over the assembly of the rods and insulated conductors. The jacket is extruded offset slightly from the twisted bundle so as to cause portions of each turn of the helix to be exposed to the exterior.

A hydrocarbon liquid pumped through the annular clearance will thus contact the exposed portions of the rods, causing them to swell to frictionally grip the coiled tubing. Clearances remain between the rods.

To avoid a problem of a length differential between the electrical cable and the coiled tubing while wound on a reel, in one embodiment the electrical conductors are twisted into a helix having a fairly high pitch.

The pitch provides a longer overall length for the insulated conductors than the coiled tubing. Also, each insulated conductor is encased within a soft compliant layer. When coiled on a reel, the soft compliant layer and the helical twist allow movement of the electrical cables relative to the jacket to account for a radius differential.

Various embodiments of the prsent invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a partial perspective view illustrating a first embodiment of a power cable constructed in accordance with this invention and shown prior to final assembly.

Figure 2 is a schematic sectional view illustrating the power cable of Figure 1, shown after final assembly and installed on a storage reel.

Figure 3 is a sectional view of the power cable in Figure 1, shown after final assembly and taken along the line 3-3 of Figure 1.

Figure 4 is a transverse sectional view of a second embodiment of a power cable constructed in accordance with this invention and shown prior to final assembly.

Figure 5 is a sectional view of the power cable of Figure 4, shown after final assembly.

Figure 6 is a transverse sectional view of a third embodiment of a power cable constructed in accordance with this invention and shown prior to final assembly.

Figure 7 is a sectional view of the power cable of Figure 6, shown after final assembly.

Figure 8 is a transverse sectional view of a fourth embodiment of a power cable constructed in accordance with this invention, taken along line 8 - 8 of Figure 10 and shown prior to final assembly.

Figure 9 is the same sectional view of the power cable of Figure 8, but shown after final assembly.

Figure 10 is a sectional view of the power cable of Figure 8, shown prior to final assembly, and with a portion of the coiled tubing broken out to illustrate the electrical cable within.

Figure 11 is a transverse sectional view of a fifth embodiment of a power cable constructed in accordance with this invention and shown after final assembly.

Figure 12 is a sectional view of the power cable of Figure 11 with a portion of the coiled tubing removed to illustrate the electrical cable located within.

Referring to Figure 1, power cable 11 includes a coiled tubing 13. Coiled tubing 13 is a continuous length of steel tubing which may be thousands of feet in length. Coiled tubing 13 is of a type that can be stored on a large reel and deployed into a well. Coiled tubing 13 has a cylindrical inner diameter 15.

An electrical cable is located within coiled tubing 13. The electrical cable includes three copper conductors 17. Each conductor 17 is insulated with its own insulation layer 19. Insulation layer 19 is conventional and of an elastomer that has high dielectric properties, such as an EPDM rubber (ethylenepropylene-diene monomer terpolymer). A compliant layer 21 is extruded over each insulation layer 19. Each compliant layer 21 is of an elastomeric material that is approximately the same thickness as insulation layer 19 but is softer and more resilient. Compliant layer 21 preferably has a hardness of 60-80 Shore A, while insulation layer 19 has a hardness typically in the range from 85-95 Shore A. Compliant layer 21 may also be an EPDM rubber with a lower level of cross-linking than insulation layer 19 to reduce the hardness. Other polymers may also be suitable, such as nitrile rubber.

An elastomeric jacket 23 is extruded around the bundle 25 of the three insulated conductors 17. Jacket 23 should have a fairly high swell compound. A high swell compound is generally defined as one that has over 100% volume change when tested in xylene for twenty-four hours at room temperature. Jacket 23 should have a swell compound that achieves at least 80% of that of a high swell compound. Also, in relation to the hardness of compliant layer 21, a typical cable jacket of this nature will have a hardness of 82-92 Shore A. A suitable material for jacket 23 and having a high swell compound is EPDM rubber of the same general type as used with insulation layer 19.

Jacket 23 has an initial outer diameter 24 upon extrusion that is less than inner diameter 15 of coiled tubing 13. In the preferred manufacturing method, coiled tubing 13 is separately manufactured, then the electrical cable comprising jacket 23 and the insulated conductors 17 is inserted into coiled tubing 13. An annular clearance 26 will exist initially between the initial outer diameter 24 of jacket 23 and inner diameter 15. A hydrocarbon liquid having a high API gravity is then pumped through annular clearance 26.

Jacket 23 swells into gripping engagement with inner diameter 15 of coiled tubing 13 as illustrated in Figure 3. The dotted lines in Figure 3 illustrate the initial outer diameter 24 prior to swelling.

Power cable 11 will be reeled on a large reel for transport to a wellsite and deployment. The length of power cable 11 may be several thousand feet, thus power cable 11 will be wrapped in many turns and layers. The centerlines of jacket 23 and coiled tubing 13 may not always coincide, as illustrated in Figure 2. This difference may occur even after a component of the electrical cable has been previously swelled into engagement with coiled tubing 13. Figure 2 illustrates a portion of one turn of a wrap of power cable 11 on a large reel. Each turn of coiled tubing 13 has a radius 29 from the axis of the reel. The same turn of electrical cable bundle 25, however, may have a slightly less radius 31 from its axis 27 to the axis of the reel.

For a given number of turns, cable bundle 25 may have a shorter length than coiled tubing 13. The different radii 29, 31, unless accounted for, thus may have the effect of making the electrical cable bundle 25 draw up within the end of coiled tubing 13 when wound on a reel, even though the lengths while previously in a straightened condition were the same.

To account for this difference, bundle 25 is twisted into a tight helix, as shown in Figure 1, that has a higher pitch than normally employed for conventional electrical power cable used with electrical submersible pumps. In the preferred embodiment, this pitch is not more than ten inches. The twist creates a considerably greater overall length for conductors 17 than coiled tubing 13. When coiled on a reel as shown in Figure 2, the compliant layers 21 accommodate radial movement of conductors 17 relative to jacket 23.

Compliant layers 21 and the tight helical twist of bundle 25 tend to cause the centerlines of cable bundle 25 and coiled tubing 13 coincide, avoiding the ends of the electrical cable from drawing up within the ends of coiled tubing 13 when coiled on a reel.

Referring to Figure 4, power cable 33 is the second embodiment and it, as well as the other embodiments, may be combined with the embodiment of Figure 1 if desired.

That is, although there are no compliant layers shown such as compliant layer 21 (Fig. 1), such may be employed. Moreover, it may also have a tight helix as in Figure 1. Power cable 33 is located within metal coiled tubing 35 of the same type as coiled tubing 13.

Coiled tubing 35 has an inner diameter 37. Conductors 39 have separate insulation layers 41. The bundle of insulated conductors 39 has an extruded elastomeric jacket 43 over them. Jacket 43 is an elastomeric material, such as that of Figure 1, which has a fairly high swell compound.

Jacket 43 has an outer diameter 45 that is initially less than inner diameter 37 of coiled tubing 35. This results in an annular clearance 47 for the passage of a hydrocarbon liquid to cause jacket 43 to swell. So as to avoid annular clearance 47 from prematurely closing before the full length of jacket 43 has been exposed to the hydrocarbon, a plurality of grooves 49 are formed in the exterior of jacket 43.

Grooves 49 are shallow regularly spaced grooves formed by the extrusion die of jacket 43 during the extrusion process. Grooves 49 preferably may extend longitudinally parallel with the longitudinal axis of jacket 43.

Figure 5 shows the final assembly of power cable 33. Jacket outer diameter 45 will be in engagement with coiled tubing inner diameter 37. At least some portions of the grooves 43 remain open after full swelling, so as to assure that a flow path exists for the hydrocarbon liquid along the full length of the power cable 33.

Power cable 51 of Figures 6 and 7 represents a third embodiment of this invention. Power cable 51 has the same metal coiled tubing 53 as all the other embodiments. Coiled tubing 53 has an inner diameter 55.

A plurality of electrical conductors 57 have insulation layers 59 of the same type as in the other embodiments.

A jacket 61 is extruded over the three insulated conductors 57. In this embodiment, however, jacket 61 is comprised of an elastomeric compound that is resistant to swelling when contacted by a hydrocarbon liquid. Materials of this type are conventionally used for cable jackets. One suitable material is nitrile rubber. Jacket 61 has an outer diameter 63 that is initially less than coiled tubing inner diameter 55, providing annular clearance 63 as shown in Figure 6.

A gripping member 67 is bonded to jacket 61 to grip coiled tubing 53 to support the weight of the electrical cable. Gripping member 61 in this embodiment is a longitudinally extending strip mounted in a groove 69 formed in jacket 61. In transverse cross-section, gripping member 67 is in the configuration of a segment of a ring, having curved inner and outer surfaces 72, 74 and two side edges 71, 73. In the preferred embodiment, the radius of outer surface 74 is initially the same as the radius of jacket 61. Side edges 71, 73 are spaced apart to provide a circumferencial length that is much less than 360 degrees. In the embodiment shown, the circumferencial length is about 90 degrees. Gripping member 67 is formed of a material which is elastomeric and which has a fairly high swell compound.

After installation, when a hydrocarbon liquid is pumped through annular clearance 65, gripping member 67 will swell, as shown in Figure 7, into tight gripping contact with a portion of the coiled tubing inner diameter 55. Portions of annular clearance 65 remain even after gripping member 67 has fully swelled, as shown in Figure 7, to assure that the hydrocarbon liquid reaches all of gripping member 67. Preferably, gripping member 67 is formed separately then bonded into previously formed groove 69 in jacket 61.

Referring to Figures 8 - 10, power cable 75 illustrates a fourth embodiment of this invention.

Power cable 75 includes metal coiled tubing 77 of the same type as in the other embodiments. Coiled tubing 77 has an inner diameter 79. Three conductors 81, each having a conventional insulation later 83, will be separately formed. Jacket 85 will be extruded over conductors 81. Jacket 85, like jackets 23 (Fig. 1) and 43 (Fig. 4), is of a type that has a fairly high swell compound. A sheath 87 is extruded over jacket 85.

Sheath 87 is a layer of an elastomeric material that resists swelling when exposed to hydrocarbon liquid in a similar manner to jacket 61 of Figure 3. Sheath 87 has an outer diameter 89 that is less than coiled tubing inner diameter 79, providing an annular clearance 91. A plurality of longitudinally extending grooves 88 are formed in outer diameter 89.

As shown in Figure 10, a plurality of apertures 93 are located in sheath 87. Apertures 93 are spaced at fairly frequent intervals along the length of sheath 87.

The electrical cable assembly including sheath 87 will be inserted into coiled tubing 77, then a hydrocarbon liquid is pumped through annular clearance 91. The liquid contacts jacket 85 through apertures 93, causing jacket 85 to swell. Sheath 87 will radially stretch as a result of the swelling to tightly grip coiled tubing inner diameter 79 as illustrated in Figure 9. Grooves 88 maintain a flow path for the hydrocarbon after sheath 87 has stretched into contact with coiled tubing 77.

Apertures 93 have a circumferential extent of less than 360 degrees, preferably around 90 degrees.

Referring to Figures 11 and 12, power cable 95 represents a fifth embodiment constructed in accordance with this invention. Power cable 95 includes coiled tubing 97 of the same type as in the other embodiments.

Coiled tubing 97 has an inner diameter 98. The electrical cable has three conductors 99, each having a conventional insulation layer 101. A jacket 103 is extruded around the bundle of insulated conductors 99.

In this embodiment, jacket 103, like jacket 61 of Figure 6, does not swell upon contact of hydrocarbon liquid.

Rather, the swelling action is through three gripping members 104. Each gripping member 104 is a cylindrical solid elastomeric rod of a material which has a fairly high swell compound. Each gripping member 104 is twisted in the same bundle 105 with the three insulated conductors 99 prior to extruding jacket 103 over the assembly. The centerline of the die for extruding jacket 103 will be deliberately set off center slightly from the centerline of bundle 105. This results in some exposed portions 106, as shown in Figure 12, which expose portions of each of the gripping members 104.

Because of the helical path of each gripping member 104 that occurs due to the helix, exposed portions 106 will not be continuous, rather each will be a portion of a helix as shown in Figure 12.

The outer diameter of jacket 103 is less than inner diameter 98 of coiled tubing 97. This creates an annular clearance 107 when the electrical cable is inserted into coiled tubing 97. Introducing a hydrocarbon liquid into annular clearance 107 causes the exposed portions 106 of gripping members 104 to swell as illustrated in Figure 11. Exposed portions 106 engage coiled tubing inner diameter 98 to support the weight of the electrical cable.

The invention has significant advantages.

Providing compliant layers around the insulated conductors and a tight helix account for differentials in lengths when the power cable is reeled onto a storage reel. This avoids the need for utilizing a much larger coiled tubing so as to put waves into the electrical cable between separate anchors. The various embodiments disclose means for supporting the weight of an electrical cable in a coiled tubing without the need for mechanical anchors. The coiled tubing need only be slightly larger than the initial outer diameter of the electrical cable. In each case, gripping occurs due to a component of the electrical cable swelling when exposed to a hydrocarbon liquid. The components of the electrical cable, but for the conductors, may all be elastomeric, yet flow paths for the hydrocarbon liquid are provided even though swelling will be occurring while the liquid is being pumped. These flow paths assure that the hydrocarbon liquid will reach the end of the power cable.

While the invention has been shown in several of its forms, it should be apparent to those skilled in the art that the invention is susceptible to various changes and modifications without departing from the scope of the invention as defined by the attached claims.

Claims (33)

Claims

1. A self-supporting power cable for an electrical submersible pump, comprising in combination: a plurality of insulated conductors, each of the insulated conductors having an insulation layer, the insulated conductors being twisted together in a helical array; at least one compliant layer extruded over the insulation layers of the insulated conductors, the compliant layer having a lesser hardness than each of the insulation layers; a jacket of an elastomeric material extruded over the compliant layer; a metal outer tubing surrounding the jacket, the jacket being supported by the tubing so that the tubing will support the weight of the power cable when installed within a well; and wherein the helical array and the compliant layer allowing limited movement of the insulated conductors within the jacket when the power cable is moved between a coiled position on a reel and an uncoiled position within the well.

2. The power cable according to claim 1, wherein the jacket includes at least a portion formed of a material which swells into supporting contact with the tubing as a result of being contacted by a hydrocarbon fluid introduced into the tubing.

3. The power cable according to claim 1 or 2, wherein: the jacket has an outer diameter that is initially less than an inner diameter of the tubing; and the material of the jacket is of a type which swells upon contact with a hydrocarbon fluid introduced into the tubing to expand the outer diameter into supporting contact with the inner diameter of the tubing.

4. The power cable according to claim 1, 2 or 3, wherein the compliant layer has a lesser hardness than the jacket.

5. The power cable according to any'preceding claim, wherein said at least one compliant layer comprises a plurality of compliant layers, each of the compliant layers separately surrounding one of the insulation layers.

6. The power cable according to any preceding claim, wherein the helical array has a pitch that is no greater than ten inches (25.4 cm).

7. A self-supporting power cable for an electrical submersible pump, comprising in combination: a metal outer tubing having an inner diameter; a plurality of conductors, each individually encased in an insulation layer; a jacket in which conductors are imbedded, the jacket having an exterior with a diameter that is initially less than the inner diameter of the tubing, the jacket being formed of an elastomeric material which swells upon contact with a hydrocarbon fluid, expanding the outer diameter of the jacket into contact with the inner diameter of the tubing to cause the tubing to support the weight of the power cable; and a plurality of grooves on the exterior of the jacket and extending longitudinally to facilitate the flow of the hydrocarbon fluid in an annular space between the exterior of the jacket and the inner diameter of the tubing.

8. The power cable according to claim 7, wherein the conductors are twisted together in a helical array, and wherein the power cable further comprises: at least one compliant layer extruded over the insulation layers of the insulated conductors, the compliant layer having a lesser hardness than each of the insulation layers, allowing limited movement of the insulated conductors within the jacket when the power cable is moved between a coiled position on a reel and an uncoiled position within the well.

9. The power cable according to claim 7, wherein the grooves are regularly spaced around a circumference of the jacket.

10. The power cable according to claim 7, wherein the grooves extend substantially perpendicular to a longitudinal axis of the power cable.

11. The power cable according to claim 10, wherein the compliant layer has a lesser hardness than the jacket.

12. The power cable according to claim 10 or 11, wherein said at least one compliant layer comprises a plurality of compliant layers, each of the compliant layers separately surrounding one of the insulation layers.

13. The power cable according to claim 10, 11 or 12, wherein the helical array has a pitch that is no greater than ten inches (25.4 cm).

14. A self-supporting power cable for an electrical submersible pump, comprising in combination: a metal tubing having a longitudinal axis and an inner diameter; a plurality of conductors, each individually encased in an insulation layer; a jacket in which conductors are imbedded, the jacket having an exterior with an outer diameter that is initially less than the inner diameter of the tubing, forming a clearance between the jacket and the tubing, the jacket being formed of an elastomeric material which resists swelling upon contact with a hydrocarbon fluid; and at least one gripping member bonded to the jacket and extending longitudinally along the jacket, the gripping member being formed of a material which swells upon contact with a hydrocarbon fluid, the gripping member having an exterior portion exposed to the clearance so that pumping a hydrocarbon fluid through the clearance causes the gripping member to swell and frictionally engage the inner diameter of the tubing for supporting the weight of the conductors with the tubing, the gripping member having a circumferential extent from one side edge to another side edge that is substantially less than 360 degrees to assure that the clearance does not become completely blocked due to swelling of the gripping member.

15. The power cable according to claim 14, wherein the gripping member extends helically along the jacket.

16. The power cable according to claim 14, wherein the gripping member comprises a strip located within a groove formed on the outer diameter of the jacket.

17. The power cable according to claim 14, wherein the gripping member is wrapped in a helix around the conductors and embedded within the jacket, each turn of the helix exposing a portion of the exterior of the gripping member to the outer diameter of the jacket.

18. The power cable according to claim 14, wherein the gripping member is wrapped in a helix around the conductors and embedded as a bundle within the jacket, the bundle having a centerline offset from a centerline of the jacket so that each turn of the helix exposes a portion of the exterior of the gripping member to the outer diameter of the jacket.

19. A self-supporting power cable for an electrical submersible pump, comprising in combination: a metal tubing having a longitudinal axis and an inner diameter; three conductors, each individually encased in an insulation layer and twisted into a helix; at least one gripping member, the gripping member being a solid flexible rod formed of a material which swells upon contact with a hydrocarbon fluid, the gripping member being twisted in a bundle along with the conductors which has a centerline; a jacket extruded over the bundle, the jacket having an exterior with an outer diameter that is initially less than the inner diameter of the tubing, forming a clearance between the jacket and the tubing, the jacket being formed of an elastomeric material which resists swelling upon contact with a hydrocarbon fluid; and the jacket having a centerline offset from the centerline of the bundle, causing a portion of the gripping member to be exposed to the clearance so that pumping a hydrocarbon fluid through the clearance causes the gripping member to swell and frictionally engage the inner diameter of the tubing for supporting the weight of the conductors with the tubing.

20. The power cable according to claim 19, wherein there are three of the gripping members.

21. The power cable according to claim 19 or 20, wherein the gripping member has a cylindrical exterior.

22. A self-supporting power cable for an electrical submersible pump, comprising in combination: a metal tubing having an inner diameter; a plurality of conductors, each individually encased in an insulation layer; a jacket in which the conductors are imbedded, the jacket having an exterior with a diameter that is initially less than the inner diameter of the tubing, the jacket being formed of an elastomeric material which swells upon contact with a hydrocarbon fluid; a sheath extruded around the jacket, the sheath being of an elastomeric material which resists swelling when exposed to the hydrocarbon fluid, the sheath having an outer diameter less than the inner diameter of the tubing, providing a clearance for the passage of the hydrocarbon fluid; and a plurality of apertures located in and spaced longitudinally along the sheath for exposing the jacket to hydrocarbon fluid pumped through the clearance, causing portions of the jacket to swell and protrude through the apertures and into gripping contact with the inner diameter of the tubing to cause the tubing to support the weight of the power cable.

23. The power cable according to claim 22, further comprising a plurality of grooves formed in the outer diameter of the sheath.

24. An electrical cable, comprising in combination: a metal outer tubing having an inner diameter; at least one electrical conductor; a jacket surrounding the conductor, the jacket being formed of a material which swells upon contact with a selected fluid medium, causing the outer diameter of the jacket to swell to tightly grip the inner diameter of the tubing; and a plurality of grooves extending along the exterior of the jacket to provide flow passages for the medium between the exterior of the jacket and the inner diameter of the tubing.

25. The cable according to claim 24, wherein the grooves extend substantially parallel to a longitudinal axis of the power cable.

26. The cable according to claim 24, wherein the grooves are regularly spaced around a circumference of the jacket.

27. A method of installing an electrical cable within a length of tubing for use in a well comprising: extruding a jacket over at least one electrical conductor and forming a plurality of longitudinally extending grooves around an exterior of the jacket, the jacket being of a material which swells upon contact with a selected fluid medium; then inserting the jacket and the conductor into the tubing; then flowing the medium through the grooves which causes the jacket to swell into tight contact with tubing.

28. The method according to claim 27, wherein the step of extruding a jacket comprises forming the jacket with an outer diameter which is initially less than an inner diameter of the coiled tubing to provide an initial annular clearance between the jacket and the tubing.

29. A self-supporting power cable for an electrical submersible pump, comprising: a plurality of insulated conductors, each of the insulated conductors having an insulation layer, the insulated conductors being twisted together in a helical array; at least one compliant layer extruded over the insulation layers of the insulated conductors, the compliant layer having a lesser hardness than each of the insulation layers; a jacket of an elastomeric material extruded over the compliant layer; and a metal outer tubing surrounding the jacket.

30. A self-supporting power cable as claimed in claim 29, wherein the jacket swells, in use, into engagement with the metal outer tubing.

31. A self-supporting power cable for an electrical submersible pump, comprising: a metal outer tubing; at least one conductor; a jacket in which said at least one conductor is embedded, the jacket constituting or being provided with supporting means formed of an elastomeric material; wherein upon contact with a hydrocarbon fluid the supporting means swells so that said metal outer tubing supports the weight of the power cable, the supporting means being configured to engage the inner surface of the metal tubing around only a part of its inner circumference so as to define at least one hydrocarbon fluid access passage along the length of the power cable.

32. A self-supporting power cable substantially as hereinbefore described with reference to the accompanying drawings.

33. A method of installing an electrical cable within a length of tubing for use in a well substantially as hereinbefore described with reference to the accompanying drawings.