SK500632019A3 - Power cables for electric submersible pump - Google Patents

Abstract

The present invention discloses a three-phase drilling pump power cable comprising three electrical conductors each provided with at least one extruded polymeric insulating layer made of an insulating polymer selected from an ethylene copolymer or fluoropolymer, a metal tube in a radial outer position relative to the insulating layer and extruded layer in which three electrical conductors are located and is made of a fluoropolymer.

Description

Technical field

The present invention provides a power cord socket for electric submersible pump (ESP) systems.

Prior art

ESP systems contain both drilling and surface components. ESP drilling components include motor, protectors, pump sections, pump inlets, power cables, gas handling equipment and drilling sensors. Surface components include pump control devices such as variable speed drives (VSDs) and a power source that is connected to the system's pump motor by armored cables.

In many areas of application, ESP systems provide several operational benefits. The pumps can be made of high quality, corrosion resistant metal alloys for use in borehole environments with high gas to oil ratio (GOR) fluids, high temperatures and fluids containing corrosive acid gases. However, several operational challenges should be considered when operating ESP. Although ESP systems can be made with special abrasion-resistant metal alloys and upgraded radial bearing materials and configurations, ESP operating times can be seriously endangered in environments with high solids and carbon content.

A typical ESP system generally includes an electric submersible pump (ESP) to be located at the bottom of the borehole, several kilometers deep, connected to a piping system for transporting production fluid (oil) to the surface. The ESP motor has three-phase alternating current (AC) and is driven by a cable connection to the power supply and control system on the well surface. As http://petrowiki.org/Electrical_submersible_pumps states, ESP power cables are specially designed three-phase power cables that are designed specifically for the well environment. The cable construction should be small in diameter, protected from mechanical damage and resistant to physical and electrical damage due to the aggressive borehole environment. They can be made in a circular or flat configuration, using several different insulation materials and metal armor materials for different hostile well environments. Usually, these cables have a lifespan of up to 3 years.

ESP power cords typically carry AC current of up to 200 A or more, depending on ESP power requirements.

US 2012/0093667 relates to power cables used to transmit electricity to electric submersible pumps (ESPs), in particular a power cable suitable for installation in environments where the temperature is continuously in the range of about 260 degrees Celsius (500 degrees Fahrenheit). The power cable according to this reference has three electrical conductors and an insulator comprising at least two insulating layers made of the same or different material, for example polyimide or fluoropolymer. The protective sheath is located above the insulated conductor and can be made of a metallic material such as stainless steel or Monel. The insulated and sheathed conductors are interconnected by wrapping with an outer layer, which may be constructed of a metallic or non-metallic material.

US 2007/0046115 relates to a power cable for supplying power to the pump motor of electric submersible pump assemblies. The electrical wiring consists of two parts, the motor conductor and the power cable. The motor conductor is configured such that each insulated conductor is housed in a separate metal impermeable tube formed of a non-electromagnetic material, such as Monel or stainless steel. Preferably, each conductor has at least two insulating layers, of which at least one can withstand high temperatures. The tubes are coated with a metal armor.

WO 2015/077207 relates to a cable for a drilling rig. As an example, an ESP flat cable of about 5 kV may include a copper conductor (s), oil and heat resistant EPDM rubber insulation, a barrier layer (e.g. lead and / or fluoropolymer), a sheath layer (e.g. oil resistant EPDM or nitrile rubber) ) and armor (eg galvanized or stainless steel or alloys containing nickel and copper, such as Monel fluids).

To ensure optimum ESP performance, drilling sensors can be installed that continuously acquire real-time system measurements, such as supply and discharge pressures and pump temperatures, vibrations, and leakage rates.

Tube-encapsulated (TEC) cables are used to provide energy and signal transmission to and from drilling sensors and surface data acquisition units. The TEC is designed for harsh well environments and may contain a layer (s) of polymeric encapsulation for protection. Different TEC configurations are available depending on the well environment and application.

For example, a TEC suitable for operation in harsh environments at temperatures up to 300 ° C is given in the brochure, "Cable encapsulated cable" (2013) from the applicant. This TEC contains a copper conductor gradually coated with an insulating layer of fluorinated ethylene propylene (hEH), polypropylene filler, alloy tube

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825 and a perfluoroalkoxy encapsulation. These cables have a conductor size of 18 AWG to 8 AWG (corresponding to a cross-sectional area of 0.52 mm ² to 8.36 mm ² ) and typically carry a direct current (DC) of 5 to 20 mA. These cables can be used as individual cables or arranged in a flat sheath construction with other components, including optical fibers, copper signal cables, hydraulic control and chemical injection lines, as well as possible mechanical components to increase crush resistance and provide additional longitudinal strength. In this case, the encapsulation collectively surrounds all the components of the flat housing.

The essence of the invention

There is a need for a power cable for operating the ESP system, in particular for supplying power to the pump system motor, which has an increased service life, for example longer than 5 years, in a demanding environment, especially at temperatures above 200 ° C.

The Applicant has noticed that the available ESP cables generally provide a limited service life, on the order of several months or at most several years, after which it is necessary to select the entire ESS twist system for cable replacement. This significantly increases costs and labor.

Currently available ESP cables are subject to early failure due in part to a corrosive chemical environment and ambient temperature.

In an ESP cable, protection against chemical corrosion can be achieved by providing a lead sheath or alternatively a layer made of chemically resistant polymers, such as fluoropolymers, around the conductors.

However, if lead is used, due to its poor mechanical properties, additional mechanical protection is required, generally in the form of an additional helically wound metal layer of tape, which increases the cost and weight of the cable.

When protection is provided by chemically resistant polymers, the Applicant has found that this chemical resistance may be reduced during the service life of the cable.

In addition, the Applicant has found that when current, especially AC, is transmitted to the cable to operate the pump system motor, heat is generated in the cable due to the Joule effect, insulation losses, etc., which cause the temperature to rise. The heat resistance of the polymers around the conductors prevents the heat dissipation of the conductors. As a result, the internal temperature of the cable can rise harmfully during operation. In addition, some chemically resistant polymers do not provide electrical properties suitable to allow sufficient life at the applied voltage.

Applicant has found that the extended life of a three-phase power cable for an ESP system that even operates at a high temperature (above 200 ° C) can be obtained by providing a cable in which each conductor insulation contains a specific polymer layer and is arranged in a welded metal tube and a common layer of fluoropolymer for encapsulation surrounding the three phases.

This allows the selection of insulating materials on the basis of heat resistance and electrical properties, while chemical protection as well as mechanical protection is achieved by a welded metal tube surrounded by a layer of fluoropolymer for encapsulation.

Therefore, the present disclosure includes a three-phase drill pump power cable comprising three electrical conductors, each of which is 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 a radially outer position relative to the insulating layer; and an extruded encapsulation layer in which three electrical conductors are embedded and is made of a fluoropolymer.

In the following text, each electrical conductor surrounded by at least one insulating layer will be referred to as an "insulated conductor".

In the following text, each insulated conductor surrounded by a metal tube will be referred to as a "cable core".

The power cables of the present invention are particularly suitable for powering electric submersible pump (ESP) systems, more particularly motors of ESP systems.

The power cables according to the invention are particularly suitable for alternating current (AC) transmission.

The power cables of the present invention may have a circular or flat cross-section. In the case of a circular cross-section, the three cable cores are preferably tied together. In the case of a flat cross-section, the three cable cores are preferably in a mutually planar arrangement (parallel and arranged in a common plane).

In the power cables of the present invention, each of the electrical conductors may have a size of at least 6 AWG (13.3 mm ² ); preferably, each of the electrical conductors can be up to 2/0 AWG (67.4 mm ² ) in size.

Each electrical conductor can be made of copper or aluminum in the form of braided cables or a solid rod.

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In one embodiment, the insulating ethylene copolymer is an ethylene-propylene-diene monomer (EPDM) copolymer. Such embodiments may be advantageous, for example, when a higher voltage is required for the cable.

In another embodiment, the insulating fluoropolymer is a perfluoroether, such as a fluoroalkyalkane (PFA). In other embodiments, the insulating fluoropolymer is a high purity fluoropolymer having impurities less than 40 microns.

In one embodiment, the cable comprises two insulating layers, hereinafter referred to as inner and outer extruded insulating layers. A two-layer insulation system may be used if it is known or suspected that impurities are present in the insulation material (s); the presence of two layers minimizes the distribution of contamination in a particular cross section.

Each individual or inner insulating layer of the cable can be extended around and in direct contact with the respective electrical conductor.

The inner and outer extruded insulating layers of the cables of the present invention may be made of different insulating polymers or of the same insulating polymer.

In one embodiment, the insulating polymer (s) is / are coextruded. Coextrusion of the insulating polymer (s) can increase the adhesion between the inner and outer insulating layers.

In some embodiments, each metal cable tie made of a nickel-iron-chromium alloy, such as a titanium-stabilized austentic nickel-iron-chromium alloy, is optionally enriched with molybdenum and copper. For example, in some embodiments, the metal seal may be made of an Incoloy® alloy, preferably Incoloy® 825.

In some embodiments, each metal cable gland is provided around the insulated conductor, preferably in direct contact with the insulating layer (in the case of single-layer insulation) or with the outer insulating layer (in the case of double-layer insulation).

In some embodiments, each metal sheath of the cable has a wall thickness of from 0.5 to 2.5 mm

The metal seals are preferably provided for the cable according to the following procedure. The cold-rolled metal strip is formed into a sealing arrangement around the insulated conductor and is longitudinally welded with a seam, for example using tungsten gas arc welding. The sealing is welded with a seam having an outer diameter larger than the insulated conductor to protect against heat generated by the welding operation, and it is cold drawn to the final size in contact with the insulating layer of insulated conductor.

In some embodiments, the encapsulated encapsulation layer may be made of a perfluoroethane, such as perfluoroalkoxyalkane (PFA).

The cable of the present invention is suitable for operation at temperatures up to 230 ° C or more, and supplies AC greater than 100 A, for example from 100 A to 300 A, at a voltage of from 4 kV to 10 kV.

For purposes of the present description and the appended claims, the same terms are used to describe the elements and components of the present invention. This is for the sake of clarity and to provide a general sense of the present invention. This description and claims should be understood to include one or at least one, and the singular also includes the plural unless it is obvious that it is otherwise stated.

For the purposes of the present description and the appended claims, unless otherwise indicated, all numbers expressing quantities, quantities, percentages, and so forth, are to be construed as being in all cases modified by the word "about." All ranges also include any combination of published maximum and minimum points, and include all intermediate levels that may or may not be specifically named herein.

Overview of figures in the drawings

Other characteristics will be apparent from the detailed description given below with reference to the accompanying drawings, in which:

Figure 1 shows an ESP system comprising a cable according to the present invention;

Figure 2 shows a cross section of an embodiment of a cable according to the present invention;

Figure 3 shows a cross section of another embodiment of a cable according to the present invention.

Examples of embodiments of the invention

Fig. 1 shows an example of the construction of an ESP system, showing a borehole having a housing 11 with a tube 13 and an ESP system 10.

The ESP 10 system includes an electric submersible pump (ESP) 15 (also known as a well pump, DWP) attached to the lower end of the nozzle 13. The ESP 15 is operatively connected to the motor 17, optionally via a guard 19 which prevents drilling fluids from entering the motor 17. The motor 17 is typically a three-phase motor

SK 50063-2019 Α3 AC motor designed to operate with voltages generally ranging from about 3 to about 5 kV, but ESP systems may operate at higher voltages, depending on, for example, well depth and / or heat, such as explained below.

Power is supplied to the motor 17 from the power supply and control system (ESRS) 16 (on the surface) by means of a power cable 12. To limit the movement of the cable in the well and, if necessary, to support its weight, the cable 12 may be attached to the tube 13 by means of fasteners. elements 14 in the form of strips, clamps or the like. The ESRS 16 should provide a voltage higher than the voltage required by the motor 17 to compensate for the voltage drop in the power cable, which may be significant in deep installations (e.g. deeper than 1.5 km) requiring long power cables.

Figure 2 shows an AC power cable 20 having a ribbon cable containing three electrical conductors

21. Each conductor 21 is made in the form of a solid copper rod. Wire 20 is 6 AWG, which has a nominal outer diameter of 4.12 mm. This cable is designed for 5 kV transmission.

Each electrical conductor 21 is surrounded and is in direct contact with an inner insulating layer 22 made of high purity PFA. The inner insulating layer 22 has a wall thickness of 0.51 mm. The inner insulating layer 22 is surrounded and is in direct contact with the outer insulating layer 23 made of high purity PFA. The outer insulating layer 23 has a wall thickness of 1.45 mm. The inner and outer insulating layers 22, 23 are designed for temperatures up to 250 ° C.

The metal tubes 24 are arranged to surround each outer insulating layer 23. Each metal tube 24 is made of Incoloy® 825. The metal tubes 24 have a wall thickness of 0.71 mm and an outer diameter of 9.53 mm. Each metal tube 24 may be for identification purposes. ornate and / or suppressed.

Each electrical conductor 21 with a respective inner insulating layer 22, an outer insulating layer 23 and a metal tube 24 forms a cable core 20a.

The three cable cores 20a are embedded in the encapsulation layer 25. The encapsulation layer is made of PFA. For example, the encapsulation layer 25 has external dimensions of 40 mm x 15 mm

Figure 3 shows an AC power cable 30 having a flat cable comprising three electrical conductors 31. Each electrical conductor 30 is made in the form of a solid bare copper rod. Conductor 30 is 6 AWG, having a nominal outer diameter of 4.12 mm. It may be suitable for transmitting 5 kV.

Each electrical conductor 31 is surrounded and is in direct contact with one inner insulating layer 32 made of EPDM. For example, the inner insulating layer 22 has a wall thickness of 1.96 mm

The insulating layer 32 is designed for temperatures up to 232 ° C.

Metal tubes 34 are provided to one insulating layer 32. Each metal tube 34 is made of Incoloy® 825. For example, a metal tube 34 has a wall thickness of 0.71 mm. Each metal tube 34 may be colored and / or embossed for identification purposes.

Each electrical conductor 31 with a respective insulating layer 32 and a metal tube 34 forms a cable core 30a.

The three cable cores 30a are embedded in the encapsulation layer 35. The encapsulation layer is made of PFA. For example, the encapsulation layer 35 has external dimensions of 40 mm x 15 mm

Electrical aids test

An electrical test was performed on the two AC power cables 20 in Figure 2 under 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

- Sample length: 4,572 m

Both cables did not detect any faults up to 33.4 kV AC and one of them had faults above 39.9 kV AC.

Aging test

Two AC power cables 20 according to Figure 2, 12 m long, were tested under electrical and thermal stress. The cables were subjected to 5 kV between the conductor and the metal tube for 120 days at 200 ° C.

Both cables passed the test without a hitch. Visual inspection showed no problem or signs of electrical stress on the insulation, even the color of the insulation itself was good.

Mechanical tests

The three AC power cables 20 in Figure 2 were tested according to ASTM B704 and ASTM B751 at a pulling force of about 44 kg. The results are shown in Table 1.

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Table 1

sample Yield strength, ksi (MPa) Tensile strength (%) 1 128.2 (883.9) 155.9 2 135.2 (932.2) 161.1 3 136.7 (942.5) 162.1

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

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

In the most conservative evaluation, the tested cables according to the present invention exceed the pressure values of 50 N / mm ² by a factor of 1.4. Typically, the pressure can be exceeded by a factor of 2.10.

Claims (13)

PATENT CLAIMS A three-phase drill pump power cable (20, 30) comprising three electrical conductors (21, 31), each of which is provided with at least one extruded polymeric insulating layer (22, 32) made of an insulating polymer selected from ethyl acetate. a copolymer or fluoropolymer; a metal tube (24, 34) in a radially outer position relative to the insulating layer (22, 32) and an extruded encapsulation layer (25, 35) in which the three electrical conductors (21, 31) are located and is made of a fluoropolymer. The power cable (20, 30) according to claim 1, having a round or flat cross section. The power cable (20, 30) of claim 1, wherein the conductor size is at least 6 AWG. The power cable (20, 30) according to claim 1, wherein the size of the conductor is up to 2/0 AWG. The power cable (20, 30) of claim 1, wherein the insulating polymer is ethylene-propytonediene monomer. The power cable (20, 30) according to claim 1, wherein the insulating fluoropolymer is a perfluoroether, preferably a fluoroalkoxyalkane. The power cable (20, 30) according to claim 1, wherein the insulating fluoropolymer has a high purity and impurities with a size of less than 40 μm. The power cable (20, 30) according to claim 1, comprising an inner extruded insulating layer (22) and an outer extruded insulating layer (23). The power cable (20, 30) according to claim 8, wherein the inner extruded insulating layer (22) and the outer extruded insulating layer (23) are made of the same insulating polymer. The power cable (20, 30) according to claim 1, wherein the metal tube (24, 34) is made of an alloy of nickel, iron and chromium. The power cable (20, 30) according to claim 10, wherein the metal tube (24, 34) is made of a titanium-stabilized austenitic alloy of nickel, iron and chromium, optionally enriched with molybdenum and copper. The power cable (20, 30) according to claim 1, wherein the metal tube (24, 34) is welded by a seam. The power cable (20, 30) according to claim 1, wherein the extruded layer (25, 35) for encapsulation is made of perfluoroether, preferably perfluoroalkoxyalkane.