CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US provisional application number

62/340,032, filed on May 23, 2016, the contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates in general to power cables and more specifically to a high temperature power cable for downhole applications.

BACKGROUND

[0003] Power cables are utilized in various applications to transmit power, such as electricity, between distal locations. For example, power cables are utilized to transmit electrical power to electric submersible pumps (ESPs). Power cables are generally surrounded by insulation. That insulation can generally degrade under certain temperatures. ESPs and power cables that are deployed in wellbores, for example, may encounter high temperatures and high pressures which can degrade conventional power cables resulting in the premature failure of the power cables.

[0004] Previous attempts to address high temperature conditions have included use of multiple insulating layers constructed from materials such as a polyimide layer and a fluoropolymer layer, as is described in U.S. Patent 8,113,273, for example. However, such materials are known to have temperature limits on the order of 325° C (polyimide) and over time are susceptible to creep, thermal degradation, and permeability at high pressure. While some prior attempts indicate higher thermal ratings, over time, polymer-based and other organic materials are known to carbonize and become conductive. This carbonization typically happens within months, and such cables do not remain useful beyond a year or two. Thus, in challenging wells where high pressure and high temperature are expected, such power cables would not likely hold up for the typical service life 10 years or more. For example, in ultra deepwater applications, traditional power cables are insufficient for use with ESPs. SUMMARY

[0005] A three phase power cable for high temperature and high pressure environments includes three individual single electrical conductors. Each individual single electrical conductor includes a conductive core, mineral insulation, and a protective sheath. The mineral insulation surrounds the conductive core and is in direct contact with the conductive core. The protective sheath surrounds the mineral insulation and is in direct contact with the mineral insulation.

[0006] A wellbore installation includes an electric submersible pump (ESP) deployed in the wellbore, and power cable extending between the ESP and an electric power source. The power cable includes one or more individual single electrical conductors. Each of the individual single conductors includes a conductive core, mineral insulation, and a protective sheath. The mineral insulation surrounds the conductive core and is in direct contact with the conductive core. The protective sheath surrounds the mineral insulation and is in direct contact with the mineral insulation. [0007] A system includes an ESP, an electric motor, and a power cable. The electric motor is connected to the ESP. The power cable is connected between the electric motor and an electric power source. The power cable includes one or more individual single electrical conductors. Each individual single electrical conductor comprises a conductive core, mineral insulation, and a protective sheath. The mineral insulation surrounds the conductive core and is in direct contact with the conductive core. The protective sheath surrounds the mineral insulation and is in direct contact with the mineral insulation.

[0008] The foregoing has outlined some of the features and technical advantages in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter which form the subject of the claims herein.

BRIEF DESCRIPTION OF THE FIGURES

[0009] The foregoing and other features and aspects will be best understood with reference to the following detailed description of specific examples, when read in conjunction with the accompanying drawings, wherein: [0010] FIG. 1 is a well schematic illustrating an electric submersible pump and power cable deployed in a wellbore;

[0011] FIG. 2 is an illustration of an example of a power cable; and [0012] FIG. 3 is an illustration of another example of a power cable. DETAILED DESCRIPTION

[0013] Referring now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.

[0014] In order to provide electrical power necessary for the operation of an electrical submersible pump (ESP) from the surface, a three phase electrical power cable may be used. Each of three individual single electrical conductors is properly sized for the anticipated electrical load and fully insulated for the maximum voltage anticipated for the electrical circuit. In addition the to normal electrical stresses for an ESP application, each of the individual single electrical conductors is exposed to environmental stresses such as high temperature and high pressure. Individual single power conductors of this power cable each have a conductive core, mineral insulation, and a protective sheath. The mineral insulation surrounds the conductive core and provides the required dielectric withstand capability and is in direct contact with the conductive core. The protective sheath surrounds the mineral insulation and is in direct contact with the mineral insulation.

Additionally the protective sheath provides a hermetically sealed environment in order to promote the necessary isolation between the mineral insulation and the environment.

[0015] A wellbore installation may utilize such a three phase electrical power cable in conjunction with an ESP deployed in the wellbore. In such installation, the power cable may extend between the ESP and an electric power source at the surface. [0016] FIG. 1 is a well schematic illustrating an ESP, generally denoted by the numeral 10, deployed in wellbore 12. In the example of FIG. 1, ESP 10 includes electric motor 14, motor protector 16, and pump 18. Pump 18 is fluidly connected to the surface via production conduit 22. Power cable 24 is connected between electrical power source 26 and pump 18. [0017] Referring now to FIGs. 2-3 wherein examples of power cable 24 that are adapted for use when experiencing a high temperature for an extended period of time are illustrated. It is perceived that power cable 24 is suited for installation and functionality for at least 10 years, barring mechanical damage, in environments where temperatures are sustained at 350°C or more and pressures are sustained at 500 bar or more. In some applications, power cable 24 may be suited for installation and functionality for at least 15 years or even 20 years under such conditions. Additionally, or alternatively, functionality may be maintained for any of these time frames at temperatures of up to 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, or 700°C or more. Similarly, for any of the time frames above and any of the temperatures above, functionality may be maintained at pressures of up to 600 bar, 700 bar, 800 bar, 900 bar, 1000 bar, 1100 bar, 1200 bar, 1300 bar, 1400 bar or 1500 bar or more. It is perceived that power cable 24 of the present disclosure can withstand such temperatures and pressures for extended lengths of times without significant degradation that results in electrical faults which render the cable inoperable, as is needed for installations such as a wellbore deployed ESP.

[0018] Power cable 24 may include one or more individual single electrical conductors 38. When multiple individual single electrical conductors 38 are present, such individual single electrical conductors 38 may join to form a cable bundle. In the illustrated examples, power cable 24 includes three individual single electrical conductors 38, which may be useful for providing three-phase electric power. While the illustration indicates three individual single electrical conductors 38, one of ordinary skill in the art will appreciate that one, two, or more than three individual single electrical conductors 38 may also be useful, depending on the type of power desired.

[0019] Each individual single electrical conductor 38 may include conductive core 28 surrounded by mineral insulation 30 and protective sheath 32. Mineral insulation 30 may be in direct contact with conductive core 28. Protective sheath 32 may be in direct contact with mineral insulation 30. Such direct contact may provide advantages over prior cables utilizing films or other intermediary layers between the core, insulation, and sheath. For example, construction with direct contact between conductive core 28 and mineral insulation 30, and direct contact between mineral insulation 30 and protective sheath 32 may be simpler and more reliable as compared to construction with additional layers. Core 28 and other elements of power cable 24 are preferably constructed of inorganic materials so as to avoid damaging carbonization in high temperature and/or high pressure environments.

[0020] Referring now specifically to FIG. 2 wherein an exemplary power cable 24 is illustrated. Power cable 24 is illustrated as having three individual single electrical conductors 38 with conductive cores 28 formed of copper or other electrically conductive material such as aluminum or the like. In this example, mineral insulation 30 may be magnesium oxide (MgO), some derivation thereof, or another high temperature insulator material. Mineral insulation 30 is preferably constructed of inorganic material so as to avoid damaging carbonization in high temperature and/or high pressure environments. [0021] In the example of FIG. 2, mineral insulation 30 is suited for continuous operation while experiencing temperatures and/or pressures such as those described above. Protective sheath 32 surrounds mineral insulation 30 surrounding conductive core 28. Protective sheath 32 is constructed of a material suited for protecting conductive core 28 in the environment in which it is deployed. For example, protective sheath 32 in the illustrated examples is constructed of a material that can provide physical protection to conductive core 28 in a wellbore environment and in a high temperature environment. In some instances, protective sheath 32 may be constructed of a metallic material such as without limitation, stainless steel, duplex stainless steel, nickel iron, 825, INCOLOY 800, MONEL, carbon steel, lead or the like. The protective sheath 32 may be a seam welded metal jacket or may have similar construction. Protective sheath 32 is preferably constructed of inorganic material so as to avoid damaging carbonization in high temperature and/or high pressure environments.

[0022] The individual single electrical conductors 38 may be optionally joined to form a power cable 24 suited for the particular service. In the example of FIG. 2, three individual single electrical conductors 38 are joined by spiraling the individual single electrical conductors in a helical fashion and/or wrapping with an outer jacket 34. The outer jacket 34 may provide additional corrosion resistance and protective sheath 32 may provide additional axial strength or vice versa. Alternatively, protective sheath 32 may provide both strength and corrosion functionality. Moreover, protective sheath 32 may be of unitary construction or may be constructed of multiple sheaths, i.e., inner sheath 32a and outer sheath 32b, as illustrated in FIG. 3. The inner sheath 32a and the outer sheath 32b may be formed of the same or of different materials. When multiple sheaths 32a, 32b are used, each is preferably constructed of inorganic material so as to avoid damaging carbonization in high temperature and/or high pressure environments.

[0023] In FIG. 2, three individual single electrical conductors 38 are shown positioned and joined to form power cable 24 that has a planar shape. However, it should readily be recognized that individual single electrical conductors 38 may be positioned relative to each other in a variety of manners. For example, individual single electrical conductors 38 may form a triangular or cylindrically shaped power cable 24.

[0024] Referring now to FIG. 3, wherein another example of power cable 24 is illustrated. This example is substantially similar in construction as that described with reference to FIG. 2. One difference between this described example and the prior described example is that the individual single electrical conductors 38 are bounded together in a planer or spiraled in a helical fashion together and do not include an outer jacket 34 joining the individual single electrical conductors 38 together. For example, and without limitation, individual single electrical conductors 38 may be joined by welding or an adhesive material illustrated generally by the numeral 36. For example, in this example protective sheaths 32 are metallic and protective sheaths 32 are joined by bonding at bead 36.

[0025] In addition to the materials described above for the conductive core 28, mineral insulation 30, and protective sheath 32, other materials may be used, so long as the materials can withstand high voltage at high pressures and temperatures for a prolonged period of time. It is thought that excluding organic materials from the design of the power cable 24 is one way to accomplish such objective. When inorganic materials are used for each of the conductive core 28, mineral insulation 30, and protective sheath 32, the inorganic material of the conductive core may differ from the inorganic material of the mineral insulation, and the inorganic material of the protective sheath may differ from the inorganic material of the mineral insulation and the inorganic material of the conductive core. Notably, the conductive core 28 is illustrated as a stranded conductor. However, the conductive core 28 is preferably solid, for example formed by extrusion. [0026] There are a number of expected benefits with the design described above. For example, superior life span in harsh temperature and pressure conditions and less expensive construction as compared to mineral insulated cables incorporating multiple insulation layers. Additional benefit from utilizing this technology might be an offset of inductive losses present in the electrical system of conventional pump motor designs at power factors of 0.7 or less. It is thought that the proposed design will naturally offset these inductive losses by the capacitive nature exhibited by the magnesium oxide or other mineral insulation 30 present in these power cables 24. Accordingly, the design and complexity may be simplified in the power supply system operating the motor 14, resulting in an overall lower cost power supply system.

[0027] In a preferred design, an entire length of each individual single conductor of a three phase power cable feeding power to an ESP pump motor will be designed to successfully withstand a 19kVAC test for 15 minutes at 300°C. The test voltage may be generated from a very low frequency (VLF) testing supply operating at a frequency of 0.1 Hertz with a sinusoidal sine wave type waveform.

[0028] From the foregoing detailed description of specific embodiments, it should be apparent that a system for a high temperature power cable that is novel has been disclosed. Although specific embodiments have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects and is not intended to be limiting with respect to the scope of the claims herein. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the appended claims which follow.