Power cables for electric submersible pump

Abstract

A downwell pump three-phase power cable containing three power conductors each provided with at least one extruded polymeric insulating layer made of an insulating polymer selected from an ethylene copolymer or a fluoropolymer, a metal tube in radial external position with respect to the insulating layer, and an extruded encapsulating layer embedding the three power conductors and made of a fluoropolymer.

Claims

1. A downwell pump three-phase power cable, comprising: three power conductors each provided with at least one extruded polymeric insulating layer, made of an insulating polymer selected from ethylene copolymer or fluoropolymer; three metal tubes wherein each metal tube individually encapsulates each of the three power conductors and is set in radial external position with respect to the insulating layer; and an extruded encapsulating layer embedding the three metal tubes and made of a fluoropolymer, wherein said extruded encapsulating layer is the outer-most layer of said power cable.

2. The power cable according to claim 1, having a round or a flat cross-section.

3. The power cable according to claim 1, wherein the conductor size is of at least 6 AWG.

4. The power cable according to claim 1, wherein the conductor size is up to 2/0 AWG.

5. The power cable according to claim 1, wherein the insulating polymer is ethylene propylene diene monomer.

6. The power cable according to claim 1, wherein the insulating fluoropolymer is a perfluoroether.

7. The power cable according to claim 1, wherein the insulating fluoropolymer is a high purity one having impurities of size lower than 40 μm.

8. The power cable according to claim 1, comprising an inner extruded insulating layer and an outer extruded insulating layer.

9. The power cable according to claim 8, wherein the inner extruded insulating layer and the outer extruded insulating layer are made of the same insulating polymer.

10. The power cable according to claim 1, wherein each metal tube is made of a nickel-iron-chromium alloy.

11. The power cable according to claim 10, wherein each metal tube is made of a titanium-stabilized austenitic nickel-iron-chromium alloy, optionally added with molybdenum and copper.

12. The power cable according to claim 1, wherein each metal tube is seam welded.

13. The power cable according to claim 1, wherein the extruded encapsulating layer is made of a perfluoroether.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further characteristics will be apparent from the detailed description given hereinafter with reference to the accompanying drawings, in which:

(2) FIG. 1 illustrates an ESP system including a cable of the present disclosure;

(3) FIG. 2 shows a cross-section of an embodiment of a cable of the present disclosure;

(4) FIG. 3 shows a cross-section of another embodiment of a cable of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 shows an example of an ESP system construction, wherein a well is shown having a casing 11 with a tubing 13 and an ESP system 10 provided therein.

(6) The ESP system 10 comprises an electric submersible pump (ESP) 15 (also known as down well pump, DWP) secured to the lower end of the tubing 13. ESP 15 is operatively connected to a motor 17, optionally through a protector 19 which prevents well fluids from entering the motor 17. Motor 17 is typically a three-phase alternate current (AC) motor designed to operate with voltages generally ranging from about 3 to about 5 kV, but ESP systems can operate at higher voltages, depending, for example, on the well depth and/or heat, as explained below.

(7) Power is provided to the motor 17 from an electric supply and regulation system (ESRS) 16 (on the surface), via a power cable 12. To limit cable movement in the well and, when needed, to support its weight, the cable 12 may be secured to the tubing 13 by fasteners 14, in form of bands, clamps or the like. The ESRS 16 should provide a voltage higher than that required by the motor 17 to compensate for a voltage drop in the power cable, which can be significant in deep installations (e.g. deeper than 1.5 km), requiring long power cables.

(8) FIG. 2 illustrates an AC power cable 20 having a flat cable comprising three power conductors 21. Each conductor 21 is made in form of a solid copper rod. The conductor 20 is a 6 AWG having a nominal outer diameter of 4.12 mm. Such cable is rated for carrying 5 kV.

(9) Each power conductor 21 is surrounded and in direct contact with an inner insulating layer 22 made of a high purity PFA. The inner insulating layer 22 has a wall thickness of 0.51 mm.

(10) The inner insulating layer 22 is surrounded and in direct contact with an outer insulating layer 23 made of a high purity PFA. The outer insulating layer 23 has a wall thickness of 1.45 mm.

(11) The inner and outer insulating layers 22, 23 are rated for a temperature up to 250° C.

(12) Metal tubes 24 are provided to surround each outer insulating layer 23. Each metal tube 24 is made of Incoloy® 825. Metal tubes 24 having a wall thickness of 0.71 mm and an outer diameter of 9.53 mm. Each metal tube 24 can be coloured and/or printed for identification purposes.

(13) Each power conductor 21 with the relevant inner insulating layer 22, outer insulating layer 23 and metal tube 24 forms a cable core 20a.

(14) The three cable cores 20a are embedded in an encapsulating layer 25. The encapsulating layer is made of a PFA. For example, the encapsulating layer 25 has outer dimensions of 40 mm×15 mm.

(15) FIG. 3 illustrates an AC power cable 30 having a flat cable comprising three power conductors 31. Each conductor 30 is made in form of a solid bare copper rod. The conductor 30 is a 6 AWG, having a nominal outer diameter of 4.12 mm. It can be suitable for carrying 5 kV.

(16) Each power conductor 31 is surrounded and in direct contact with a single inner insulating layer 32 made of an EPDM. For example, the inner insulating layer 22 has a wall thickness of 1.96 mm.

(17) The insulating layer 32 is rated for a temperature up to of 232° C.

(18) Metal tubes 34 are provided to the single insulating layer 32. Each metal tube 34 is made of Incoloy® 825. For example, metal tube 34 has a wall thickness of 0.71 mm. Each metal tube 34 can be coloured and/or printed for identification purposes.

(19) Each power conductor 31 with the relevant insulating layer 32 and metal tube 34 forms a cable core 30a.

(20) The three cable cores 30a are embedded in an encapsulating layer 35. The encapsulating layer is made of a PFA. For example, the encapsulating layer 35 has outer dimensions of 40 mm×15 mm.

(21) Electric Breakdown Test

(22) On two AC power cables 20 of FIG. 2 an electric breakdown test was carried out using the following conditions: Initial test voltage: 7.8 kV AC Step Voltage: 3.2 kV AC Test Time: 5 minutes at each test voltage Finish: Sample breakdown Specimen Length: 4.572 m.

(23) Both cables experienced no breakdown up to 33.4 kV AC, and one of them had a breakdown over 39.9 kV AC.

(24) Aging Test

(25) Two AC power cables 20 of FIG. 2, 12 m long, were tested under electric and thermal stress. The cables were subjected to 5 kV between the conductor and the metal tube for 120 days at a temperature of 200 OC.

(26) The test was successfully passed by both cables with no breakdown. The visual inspection showed no problem or sign of electric stress on the insulation, even the colour of the insulation itself was good.

(27) Mechanical Tests

(28) Three AC power cables 20 of FIG. 2 were tested according to ASTM B704 and ASTM B751, at a pull-out force of about 44 kg. The results are set forth in Table 1.

(29) TABLE-US-00001 TABLE 1 Sample Yield strength, ksi (MPa) Ultimate tensile strength (%) 1 128.2 (883.9) 155.9 2 135.2 (932.2) 161.1 3 136.7 (942.5) 162.1

(30) The calculated external collapse pressure (per American Petroleum Institute, API 5C3) based on worst case dimensions and minimum yield strength is 10,324 psi.

(31) The calculated external collapse pressure (per API 5C3) based on nominal dimensions and typical yield strength (120 ksi; 827.4 MPa) is 15.258 ksi (105.2 MPa).

(32) In the most conservative rating the tested cables of the present disclosure exceed the pressure rating of 50 N/mm.sup.2 by a factor of 1.4. Typically, the pressure can be exceeded by a factor of 2.10.