OF A WELL BORE

FIELD

This disclosure relates generally to the field of electrical submersible pumps (ESPs) used to lift fluids out of well bores drilled through subsurface formations. More specifically, the disclosure relates to a cable system and method for deploying an ESP into a well bore and through a well bore tubing.

BACKGROUND

Small diameter ESPs including high power density electric motors and high speed centrifugal pumps have been developed for use in well bores. Such small diameter motors and pumps can be, for example, less than 2.75 in. in diameter, and therefore suitable to be deployed into, for example, a 3.5 in. well bore tubing. These ESPs can have an inverted configuration so that the motor is uphole (closer to the surface end of the well bore) from the pump. In this case, the ESP can be deployed using electrical power cable.

Using conventional cable to deploy such small diameter ESPs would require full-size surface equipment, because the weight of the cable will be excessive, even though the weight of the downhole assembly is much reduced. Conventional steel strength members will also add significantly to the cable weight and therefore increase load requirements of the surface equipment even further. For example, in the case of a pump deployed to 5,000 ft., a typical ESP cable for such a pump is strongly reinforced with high tensile strength steel armouring, as a result of which it weighs about 1 ,350 Ib./kft. (in air). The surface equipment in this case, which consists of a winch, sheaves, and other cable handling equipment, must be capable of a winch pull of 7,400 lb. just to support the weight of the cable and ESP.

Many so-called wireline deployed ESPs use a power cable permanently fixed to the outside of the tubing, which is fitted when the tubing is run in, and use downhole electrical wet connect arrangement to provide electrical power to the pump. This adds cost and complexity, has to be run in as part of the tubing string, and carries an additional risk of unreliability. In addition, such wireline ESP deployment systems do not enable replacement of the ESP without pulling the tubing out of the well bore. Further, if the cable needs to be replaced, the tubing has to be retrieved and deployed again using a workover rig.

SUMMARY

This disclosure relates to a cable for conveying an ESP into and out of a well bore, including through a tubing in the wellbore, without preparation of the tubing. The cable is lightweight and can be deployed using lightweight surface equipment.

In one illustrative embodiment, the cable may include a central strength member made of a fibre reinforced plastic and a plurality of electrical conductors forming circumferential segments disposed externally to the central strength member. A protective jacket may encapsulate the central strength member and plurality of electrical conductors.

An aspect or embodiment relates to a cable for conveying an electrical submersible pump into and out of a well bore. The cable may comprise at least one strength member comprising a core member, the core member being made of a composite material comprising a fibre reinforced plastic. The cable may comprise a plurality of electrical conductors forming circumferential segments disposed externally to the at least one strength member. The cable may comprise a protective jacket encapsulating the at least one strength member and the plurality of electrical conductors.

The cable may comprise three conductors for three phase power supply.

At least one conductor may have a solid cross-section. At least one conductor may have a hollow cross-section. Holes in at least one conductor may be filled with a filler material.

The projective jacket may have a smooth outer surface.

The fibres in the fibre reinforced plastic may be predominantly oriented at an angle of less than 60 degrees to an axial axis of the cable. The fibres in the fibre reinforced plastic may be or comprise carbon fibres.

The fibre reinforced plastic may comprise at least one of polyurethane, polystyrene, polyethylene, and epoxy.

At least one conductor may be encapsulated in insulation. The insulation comprises a plastic material. The insulation may comprise at least one of polytetrafluoroethylene, polyether ether ketone, and polyurethane. The insulation may comprise an elastomeric material. The insulation may comprise an enamel.

The projective jacket may comprise at least one layer comprising at least one of polyurethane, polyamides, polypropylene, and polyether ether ketone. The at least one strength member may be located at a centre of the cable.

The cable may comprise additional strength members made of fibre-reinforced plastic, wherein the additional strength members are placed between the electrical conductors and encapsulated by the protective jacket.

The cable may be sized for passage through a well bore tubing.

An aspect or embodiment relates to a method for conveying an electrical submersible pump through a wellbore. The method may comprise securing an electrical submersible pump to a cable, and manipulating the cable to convey the pump through a wellbore. The method may comprise securing a pump to a cable defined in any other aspect.

The method may comprise powering the pump via the cable

It is to be understood that both the foregoing summary and the following detailed description are exemplary. The accompanying drawings are included to provide a further understanding of this disclosure and are incorporated in and constitute a part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

FIG. 1 shows a cable attached to an ESP. FIG. 2 shows a cross-section of the cable of FIG. 1 according to one illustrative embodiment.

FIG. 3 shows a cross-section of the cable of FIG. 1 according to another illustrative embodiment.

FIG. 4 shows a conductor with a hollow cross-section.

FIG. 5 shows a conductor made of a plurality of thin wires. FIGS. 6-1 1 show cross-sections of the cable of FIG. 1 according to other illustrative embodiments.

DETAILED DESCRIPTION FIG. 1 shows a cable 10 attached to an electrical submersible pump (ESP) 12. The ESP includes at least a motor 14 and a pump 16 and may have other parts not specifically identified but known in the art, such as a protector (not shown separately). The cable 10 is designed for deploying the ESP 12 into a well bore, and retrieving the ESP 12 from the wellbore, and for powering the motor 14 of the ESP 12. In one embodiment, the ESP 12 is a small diameter ESP that is sized for conveyance through a tubing (not shown) in the well bore. In one embodiment, the cable 10 has a corresponding small diameter to enable it to pass through the tubing in the well bore while attached to the ESP 12. In one embodiment, the cable 10 is used to supply three phase electrical power to the motor 14 of the ESP 12. In one embodiment, the cable 10 is designed to be lightweight but strong enough to support the weight of the ESP 12 at any desired depth in the well bore. In one embodiment, the cable 10 is designed to be flexible such that it may be wound on a reel and extended from the reel as needed to deploy the ESP 12 into the well bore. The end of the cable 10 attached to the ESP 12 may include a suitable adapter 16 for electrically coupling the cable 10 to the motor 14 of the ESP 12.

FIG. 2 shows an example cross-section of one embodiment of the cable 10. The cable 10 in FIG. 2 may have a substantially circular cross-section to enable passage of the cable 10 through certain types of well pressure control equipment (not shown) disposed at the upper end of the well bore. In FIG. 2, the cable 10 includes a central strength member 13, which in one embodiment may include a core member 15 made of composite material and a layer of high temperature elastomer 17, such as rubber or flexible polyurethane, surrounding the core member 15. The high temperature elastomer 17 may be used to form a pressure seal around the composite material core member 15.

The composite material of the core member 15 may in one embodiment be a plastic matrix reinforced with elongate, high modulus fibres, i.e., a fibre reinforced plastic. In one example, the high modulus fibres may be carbon fibres. In one embodiment, the matrix material may be a thermosetting resin or thermoplastic. In one embodiment, the matrix material is selected from polyurethane, polystyrene, polyethylene, epoxy, and any combinations of these materials. The use of composite material for the core member 15, as described above, may allow a strong, flexible, and lightweight cable 10. The diameter of the composite core member 15 can be selected to reduce the overall weight of the cable 10 in liquid for a selected cable tensile capacity. In one embodiment, the fibres in the composite material core member 15 may be predominantly oriented at an angle of less than 60 degrees to an axial or longitudinal axis of the cable 10. The cable 10 may further include electrical conductors 18, shaped in the form of circumferential segments, arranged around the core member 15. In one embodiment, the central strength member 13 has a round cross-section, and the segments of conductors 18 are shaped to form a ring cross-section around the central strength member 13. The conductors 18 may be encapsulated in insulation 20, such as may be made from polypropylene, neoprene, TEFLON brand plastic, or other material known in the art for insulating electrical conductors exposed to high ambient temperature and hydrostatic pressure. TEFLON is a registered trademark of E. I. du Pont de Nemours and Company, Wilmington, Delaware. In one embodiment, the insulation 20 may be a plastic selected from polyamides, polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK), polyurethane or a compound containing or based on any of these materials. In another embodiment, the insulation may be an elastomer. In yet another embodiment, the insulation material may be an enamel. The insulation 20 may be provided as one or more layers of coating on a surface of the conductors or as a sheath encapsulating the conductors. The present example embodiment of the cable 10 includes a protective jacket 22 surrounding the conductors 18 and encapsulating both the conductors 18 and central strength member 13.

In another embodiment, as shown in FIG. 3, peripheral strength members 13' in the form of flat strips may be placed between the conductors 18 and about the periphery of the central strength member 13. The peripheral strength members 13' may be radially oriented within the cable. The peripheral strength members 13' may each have a core member 15' made of a composite material and a layer of high temperature elastomer 17' surrounding the core member 15'. The composite material of the core member 15' may have the same properties as described above for the composite material core member 15. The cable construction with the peripheral strength members 15' will be stiffer in bending than the cable construction with only the central strength member 15, i.e., because the composite material of the peripheral strength members 15' is disposed at a greater radius from the centre of the cable. The construction with the peripheral strength members 15' can be advantageous for certain operational conditions where maximum flexibility is not required but some resistance to bucking is desirable.

In the example shown in FIG. 2, the cable 10 has three conductors for a three phase electrical power supply. In three phase power supply system, the three conductors each carry an alternating current, but the phase of the voltage on each conductor is displaced from each of the other conductors by 120 degrees. The conductors 18 are made of metallic material, typically copper or aluminium. The conductors 18 may have a solid cross-section in one embodiment, as shown in FIG. 2. FIG. 4 shows another embodiment of a conductor 18' that may be used in an example embodiment of the cable such as the embodiment shown in FIG. 2. The present embodiment of the conductor 18' may have a hole 24 with a selected diameter, i.e., a hollow cross-section. The conductor 18' may have more than one hole 24, and the cross-section of the hole 24 is not limited to a round cross-section. The hole 24 may be used in high electrical conductivity material conductors such as copper, where the skin effect at selected AC frequencies is such that having no electrically conductive material in the centre of the conductor 18' will not substantially affect the effective conductivity of the conductor 18'.

FIG. 5 shows an another example of a conductor 18" that may be used in the case of FIG. 2. The present example embodiment of the conductor 18" includes a plurality of small diameter, electrically conductive wire strands 26 that together comprise a conductor similar in cross-sectional area to the conductor 18 shown in FIG. 2. The strands 26 may be made from, for example, copper or aluminium as the solid conductor 18 explained with reference to FIG. 2. The conductor 18" will generally be more flexible than the solid shown at 18 in FIG. 2.

The material and cross-sectional area of the conductors 18 (FIG. 2), 18' (FIG. 4), and the hole 24 (FIG. 4) if used, may be selected to achieve the desired effective conductivity of the cable 10 at a selected alternating current frequency. The conductor 18" in FIG. 5 in some embodiments may have a hole and filler material as explained with reference to FIG. 4. Hollow cross-section conductors, such as conductor 18' shown in FIG. 4, may be used to reduce the overall weight of the cable 10 in liquid when a higher density material such as copper is used for the conductors. To reduce the possibility of collapsing the holes 24 in the conductors under bending stress, a filler material 25 may be disposed in the holes 24. The filler material 25 may be, e.g., a low density plastic, such as low density polyethylene (LDPE), or a fibre reinforced plastic. As explained above, the diameter of the holes 24 may be selected such that conductivity of the hollow cross- section conductor 18' is effectively the same as that of the solid cross-section conductor 18 in FIG. 2 at a selected alternating current frequency. The holes 24 will reduce the weight of the cable 10 in liquid but not reduce the effective conductivity of the cable 10. Solid cross-section conductors, such as conductor 18 in FIG. 2, together with lower density conductor material may be used to reduce the overall weight of the cable 10 in liquid. For example, it is possible to use aluminium conductors of cross-sectional area equal to an equivalent cross-sectional area of copper conductors at a selected alternating current frequency to reduce the weight of the cable in liquid to a selected value, while providing an equivalent electrical conductivity and current carrying capacity as copper conductors. Aluminium conductors may be solid cross-section and thereby omit the holes 24 (FIG. 4), but the additional cross-section needed for aluminium conductors is not more than that needed for copper conductors to carry the same current as copper conductors. Also, the much lower density of aluminium compared to copper would reduce the weight of the cable in liquid notwithstanding the necessary increased cross-sectional area of the conductors when made from aluminium. The protective jacket 22 may have a smooth (or slick) outer surface to enable effective sealing at a wellhead. The protective jacket 22 may also provide good wear properties to protect the composite material of the central strength member 13 and/or peripheral strength members 13' and the insulation of the conductors 18 (18') from abrasion and other wear. The protective jacket 22 may have a low friction for spooling the cable 10 into and out of the well bore. The protective jacket 22 may be made of one or more layers of material having the properties described above. In one embodiment, the protective jacket 22 is made of plastic. In one example, the plastic is selected from polyurethane, polyamides, polypropylene, PEEK, or a compound containing or based on any of these materials. The protective jacket 22 may include some metallic elements, e.g., steel wires or steel braiding, to provide additional resistance to damage by impact or abrasion. These metallic elements will be for protection and are not intended to contribute significantly to the tensile strength of the cable.

One method for manufacturing the cable includes forming a composite material core member (e.g., 13 in FIG. 2) by fibre pultrusion, followed by fully curing the matrix plastic material (e.g., thermosetting resin or thermoplastic). A layer of high temperature elastomer (e.g., 17 in FIG. 2) may then be applied around the core member by wrapping or by an extrusion process, resulting in a central strength member. Each conductor (e.g., 18 in FIG. 2) can be formed in circumferentially segmented cross- section, with space to accommodate the central strength member. The conductors may be encapsulated in a layer of insulation material (e.g., plastic, elastomer, or enamel). Then, the insulated conductors are arranged around the central strength member. A jacket (e.g., 22 in FIG. 2) may then be extruded onto the outer diameter of the cable. A coating of a selected material may be applied on the jacket. In some embodiments, the coating and/or jacket may include woven fibre braid, such as may be made from glass fibre or synthetic fibre such as ARAMID brand fibre or KEVLAR brand fibre. KEVLAR is a registered trademark of E. I. du Pont de Nemours and Company, Wilmington, Delaware. The method above may be modified for forming the embodiment shown in FIG. 2 with the peripheral strength members 13'.

The use of composite materials allows a stronger and lighter cable. An example cable includes three conductors, each having a cross-sectional area of 0.0206 in2 (6 AWG) and a 0.25-in diameter central strength member made of a composite material with a tensile strength of 200,000 Ib/in2, which provides a tensile capacity of 10,000 lb. The diameter over the conductors is very close to the standard electrical "wireline" cable diameter of 17/32 in. "Wireline" is a cable used to move well logging instruments along the interior of a well bore for measurement and well intervention operations as will be familiar to those skilled in the art. A cable as described herein uses composite material to combine tensile strength with low weight per unit length. The cable may have electrical current capacity equivalent to higher weight per unit length cables of known configurations for use with ESPs. The cable according to the present disclosure has a small cross section, e.g., small enough to pass through a well bore tubing. The cable in some embodiments has a slick surface and is flexible for spooling. The foregoing properties may allow the cable according to the present disclosure to be suitable for use in deploying a complete ESP system into a well bore, through tubing, using lightweight surface equipment, for example, a standard wireline winch and spooler, without prior preparation of the tubing. The ESP system can be retrieved through the tubing, including all electrical requirements, leaving the well bore free for interventions, sand clearing, etc. All parts of the ESP system can be retrieved for repair, overhaul, or replacement.

The cable described herein may have advantages compared to conventional composite cable constructions in which the strength members are predominantly on the outer diameter for applications where flexibility is advantageous. First, for small diameter needs, the cable construction described herein may have tensile strength and conductor cross-sectional area in a smaller diameter overall cable than conventional composite cable constructions. Secondly, the cable construction described herein may be more flexible for spooling in relation to its tensile strength than a conventional construction cable.

The lightweight of the cable, as described herein, combined with its tensile stiffness means that cable stretch is reduced. For the embodiment using a composite central strength member, the high specific strength of the composite central strength member provides a very lightweight cable that does not require additional strength members to meet the line pull requirements. The lightweight cable means that the weight of the cable in the liquid in the well bore is not significant and the line pull is available for mechanical pull operations (unsetting packers, etc.)

The small cross section and slick surface of the cable also minimize interference with the produced flow up the tubing in which the cable is installed. The conductors of the cable can advantageously be segmental cross-section within the cable, which increases the conductor packing factor and minimizes the cross-sectional area.

The cable uses materials that can withstand the high temperatures required for the manufacture of carbon fibre composites.

FIGS. 6-11 show example cross-sections of other embodiments of the cable 10. The main differences between these example cross-sections and those described above lie in the relative locations of the strength members and conductors within the cable and/or shapes of the strength members and conductors.

FIG. 6A show an example cable 10a having a central strength member 13a, which may include a composite material core member 15a surrounded by a layer of high temperature elastomer 17a. Electrical conductors 18a are arranged along a periphery of the central strength member 13a. The conductors 18a may be encapsulated in insulation 20a. The conductors 18a, with insulation, have a round cross-section in the present example. A protective jacket 22a may surround the conductors 18a, thereby encapsulating both the conductors 18a and core member 15a. An insulating filler material 30 may be disposed in the space within the projective jacket 22 not occupied by the central strength member 13 and electrical conductors 18a.

FIG. 7 shows an example cable 10b having a central strength member 13b, which may include a composite material core member 15b surrounded by a layer of high temperature elastomer 17b. The cable 10b includes peripheral strength members 13b', which may include composite material core member 15b' surrounded by a layer of high temperature elastomer 17b'. The peripheral strength members 13b' are spaced about a periphery of the central strength member 13b. The peripheral strength members 13b' have a round cross-section in the present example. Electrical conductors 18b are arranged in the spacing between the peripheral strength members 13c. The conductors 18b may be encapsulated in insulation 20b. The conductors 18b, with insulation, have a round cross-section in the present example. A protective jacket 22b may surround the insulated conductors 18b and strength members 13b' and encapsulate the insulated conductors 18b and strength members 13b', 13b. Spaces within the protective jacket 22b not occupied by the conductors 18b and strength members 13b', 13b may be filled with an insulating filler material 30.

FIG. 8 shows an example cable 10c having peripheral strength members 13c' arranged and spaced to form a ring. The peripheral strength members 13c' may include composite material core member 15c' surrounded by a layer of high temperature elastomer 17c'. Electrical conductors 18c are arranged in the spacing between the peripheral strength members 13c'. There is no central strength member in the example of FIG. 8. The conductors 18c may be encapsulated in insulation 20c. The conductors 18c, with insulation, have a round cross-section in the present example. A protective jacket 22c may surround the insulated conductors 18c and peripheral strength members 13c' and insulated conductors 18c, thereby encapsulating both the insulated conductors 18c and strength members 13c'. Spaces within the protective jacket 22c not occupied by the conductors 18c and strength members 13c' may be filled with insulating filler material 30. FIG. 9 shows the cable 10d having a central strength member 13d, which may include a composite material core member 15d surrounded by a layer of high temperature elastomer 17d. The cable 10d includes peripheral strength members 13d', each of which may be made of a composite material core member 15d' surrounded by a layer of high temperature elastomer 17d'. The peripheral strength members 13d' are spaced about a periphery of the central strength member 13d. The peripheral strength members 13d have a round cross-section in the present example. Electrical conductors 18d are arranged in the spacing between the peripheral strength members 13d. The conductors 18d may be encapsulated in insulation 20d. The conductors 18d, with insulation, have an elongated cross-section, e.g., oval or elliptical cross-section, in the present example. A protective jacket 22d may surround the insulated conductors 18d and strength members 13d', thereby encapsulating the insulated conductors 18d and strength members 13d', 13d. Spaces within the protective jacket 22d not occupied by the conductors 18d and strength members 13d, 13d' may be filled with insulating filler material 30.

FIG. 10 shows an example cable 10e having a central strength member 13e, which may include a composite material core member 15e surrounded by a layer of high temperature elastomer 17e. Electrical conductors 18e are spaced about a periphery of the central strength member 13e. The conductors 18e are arranged generally tangentially to the outer circumference of the central strength member 13e. The conductors 18e may be encapsulated in insulation 20e. The conductors 18e, with insulation, have an elongated cross-section in the present example. A protective jacket 22e may surround the insulated conductors 18e, thereby encapsulating the insulated conductors 18e and central strength member 13e. Spaces within the protective jacket 22e not occupied by the conductors 18e and strength member 13e may be filled with insulating filler material 30.

FIG. 1 1 shows an cable 10f having a central strength member 13f, which may include a composite core member 15f surrounded by a layer of high temperature elastomer 17e. Electrical conductors 18f are spaced about a periphery of the central strength member 13f. The conductors 18f are arranged generally tangentially to the outer circumference of the central strength member 13f. The conductors 18f may be encapsulated in insulation 20f. The conductors 18f, with insulation, have an elongated cross-section in the present example. Peripheral strength members 13f are arranged in the spaces between the electrical conductors 13f and about the periphery of the central strength member 13f. The peripheral strength members 13f may each include a composite material core member 15f surrounded by a layer of high temperature elastomer 17f. The peripheral strength members 13f have a round cross-section in the present example. A protective jacket 22f may surround the insulated conductors 18f and peripheral strength members 13f, thereby encapsulating the strength members 13f, 13f and conductors 18f. Spaces within the protective jacket 22f not occupied by the conductors 18f and strength member 13f may be filled with insulating filler material 30. The materials of the strength members, conductors, insulation, protective jacket, and filler material of the embodiments described in FIGS. 6-11 may be the same as the materials described above with reference to cable 10 and FIG. 2. Further, the conductors used in the embodiments described in FIGS. 6-1 1 may incorporate holes and fillers, as described for the conductor 18' in FIG. 4, or may be composed of wire strands as described for conductor 18" in FIG. 5.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.