WO2012010907A2

WO2012010907A2 - Cables for downhole use

Info

Publication number: WO2012010907A2
Application number: PCT/GB2011/051401
Authority: WO
Inventors: Philip Head
Original assignee: Artificial Lift Company Limited
Priority date: 2010-07-22
Filing date: 2011-07-22
Publication date: 2012-01-26
Also published as: GB201012319D0; WO2012010907A3

Abstract

A cable for use in hydrocarbon wells is manufactured by forming an impervious sheet material to define a plurality of recesses, introducing each of two or more conductors into a respective one of the recesses, and folding the sheet material and joining two edges thereof to form a seam. The recesses form compartments, each enclosing a substantial portion of a respective conductor, so that the conductors are separated from each other by portions of the casing which extend in-between the conductors. In alternative embodiments, the casing can be made from plastics sheet material, or both the sheet material of the casing and the conductors may be made from copper clad steel so as to avoid differential thermal expansion, in which case the casing may simply enclose the bundled conductors without separating them into compartments.

Description

Cables for downhole use

This invention relates to cables for downhole use, particularly the arrangement and housing of conductive cables.

In order to supply electric power to downhole tools in a hydrocarbon (oil or gas) well, conductive cables are usually disposed in the borehole, often secured to production tubing. It is not unusual that several separate conductors must be disposed in parallel, for example to deliver three-phase power to a motor, or to supply different tools. Usually, each conductor is surrounded by one or more insulating layers before all three conductors are secured together by wrapping them in binding tape and finally in an armour layer. In US5528824 for example, the armour layers are applied as metal strips wound around the cables arranged in a flat configuration.

Cable bound in this way is liable to be pervious to fluids in the well, damaging the conductors; also, applying armour in this way is inconvenient because it requires multiple assembly steps. The armour can also frictionally retard the cable as it is inserted into the well. If the insulation between conductors is compromised, flashover (short circuiting) can result. In addition, differential expansion between copper conductors and steel casing can result in damage.

The object of the present invention is to provide a arrangement to secure separate conductive cables together that offers good protection to the conductors and is convenient to assemble.

According to the various aspects of the present invention there are provided a cable and a method as defined in the claims. An embodiment provides a cable for use in a hydrocarbon well or borehole, comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being substantially impervious to hydrocarbon wellbore fluids; wherein the outer casing is made from sheet material and is shaped to define a plurality of compartments, each extending partially around one of the conductors so as to enclose a substantial portion thereof, such that the conductors are separated from each other by portions of the casing which extend in-between the conductors.

The sheet material provides less frictional resistance than conventional steel wire armour during deployment down the wellbore.

Advantageously, the compartments ensure that relatively even pressure is exerted at all points around the circumference of each conductor, which avoids local compression between adjacent outer surfaces of the conductors and hence potential damage to the insulation and electrical flashover between the conductors.

This advantage can be realised even where the conductors and the sheet material are made from different metals; for example, copper or copper clad steel conductors and steel casing; although in that case differential thermal expansion may be expected, the separation of the conductors makes it less likely that this will result in damaged insulation and flashover. Moreover, during manufacture, the conductors are easily arranged and drawn into the respective compartments without a preliminary step of binding the conductors together into a grouped, flat or clustered configuration.

Another embodiment provides a cable for use in a hydrocarbon well or borehole, comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being substantially impervious to hydrocarbon wellbore fluids; wherein the outer casing is made from plastics sheet material. The sheet material may be welded so as to join two edges thereof at a seam which extends longitudinally along the cable.

The sheet material may be metal. Two edge portions of the sheet material may be joined by crimping or folding so as to form a seam which extends longitudinally along the cable.

Both the sheet material and the conductors may be made from steel with a copper cladding. This ensures that the sheet material and the conductors have a similar or identical thermal coefficient of expansion, avoiding mechanical damage resulting from heating of the cable in use. Where the sheet material is a plastics material, the conductors may be copper, and due to the compatible thermal and mechanical characteristics of the two materials, damage due to differential thermal expansion resulting from heating of the cable does not occur. By using a plastics sheet material, the cable may advantageously be made relatively even more slippery so that it is more easily deployed downhole. The plastics material may be welded, e.g. by ultrasonic welding, or by heat or solvent welding. Suitable hydrocarbon resistant, impervious, weldable, high temperature, flexible engineering plastics sheet materials can be selected by those of ordinary skill in the art by reference to standard reference data well known in the art of plastics manufacture. Both plastics and metal sheet casings are advantageously substantially impervious to the wellbore fluids.

The cable may comprise at least three said conductors. They may be arranged in parallel, side by side configuration such that respective central longitudinal axes of all of the cables lie in a common plane, or in a clustered configuration such that respective central longitudinal axes of all of the cables do not lie in a common plane. Another embodiment provides a cable for use in a hydrocarbon well or borehole, comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being substantially impervious to hydrocarbon wellbore fluids; wherein the outer casing is made from sheet material, and both the sheet material and the conductors are made from steel with a copper cladding. As earlier explained, the like nature of the sheet material and the conductors avoids damage due to differential thermal expansion. Moreover, the cable is advantageously self- supporting even at great depths. Another embodiment provides a method of manufacturing a cable for use in a hydrocarbon well or borehole, the cable comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being made from sheet material and substantially impervious to hydrocarbon wellbore fluids; comprising the steps of a) forming the sheet material to define a plurality of recesses, b) introducing each of the conductors into a respective one of the recesses, and c) folding the sheet material and joining two edges thereof to form a seam, such that the recesses form compartments, each compartment enclosing a substantial portion of a respective conductor, such that the conductors are separated from each other by portions of the casing which extend in-between the conductors. As earlier explained, the novel method provides easier manufacture because there is no step of assembling the conductors together before forming the casing. The pre-formed casing defines compartments which draw the conductors into their final assembled position as the casing is folded around them. The operation is progressive along the length of the cable, so that the formed cable can be wound onto a large diameter drum or laid out flat as it is manufactured.

The casing may be folded after joining the two edges thereof so as to arrange the conductors in a desired configuration.

The cable may comprise two or more conductors, a metal layer formed around the two or more conductors, and an insulating layer between the conductors and the metal layer, the metal layer having an overlapping seam running substantial parallel to the conductors, the overlapping seam being sealed against fluids.

Preferably, the metal layer is shaped to accept the two or more conductors before the metal layer is formed over around the conductors.

Various illustrative embodiments will now be described, purely by way of example and without limitation to the scope of the claims, with reference to the following drawings, in which:

Figure 1 shows a cross sectional view of the cable at one stage of manufacture; Figure 2 shows a cross sectional view of the cable at a later stage of manufacture;

Figure 3 shows a cross sectional view of another embodiment of the cable at one stage of manufacture; Figure 4 shows a cross sectional view of the cable at a later stage of manufacture; Figure 5 shows a cross sectional view of a further embodiment of the cable at one stage of manufacture; Figure 6 shows a cross sectional view of the cable at a later stage of manufacture;

Figure 7 shows a cross sectional view of a further embodiment of the cable at one stage of manufacture; Figure 8 shows a cross sectional view of the cable at a later stage of manufacture;

Figure 9 shows a cross sectional view of a further embodiment of the cable at one stage of manufacture; Figures 10 and 11 show a cross sectional views of the cable at later stages of manufacture;

Figure 12 shows a cross sectional view of a further embodiment of the cable at one stage of manufacture;

Figures 13 and 14 show a cross sectional views of the cable at later stages of manufacture;

Figure 15 shows a cross sectional view of a further embodiment of the cable at one stage of manufacture;

Figure 16 shows a cross sectional view of the cable at a later stage of manufacture;

Figure 17 shows a cross sectional view of a further embodiment of the cable at one stage of manufacture; Figure 18 shows a cross sectional view of the cable at a later stage of manufacture; Figure 19 shows a cross sectional view of the cable and tubing in use; and

Figure 20 shows a cross sectional view of an another embodiment of cable and tubing in use.

Referring to figure 1, there is shown a cable comprising three copper clad stainless steel conductors 10, 11, 12 disposed in a flat, parallel-spaced relationship surrounded by a housing 15, the respective longitudinal central axes X of each cable lying in a common plane Y. The housing is formed of copper clad stainless steel sheet material in two similar parts, an upper housing 16 and a lower housing 17. The upper housing 16 and a lower housing 17 have scalloped cross sections so that each conductor 10, 11, 12 is surrounded by a semicircular recess or indentation 20, 21, 22 from the upper housing and 30, 31, 32 from the lower housing to almost encompass the conductors. Between each semicircular indentation 20, 21, 22 on the upper housing is a cusp region 25, 26; the lower housing 17 has similar cusp regions 35, 36. The upper housing has flat tabs 27, 28 at each end, similarly the lower housing has flat tabs 37, 38. The cross section of the housing 15 is regular and the housing will typically run for the length of the conductors; it will be understood that the semicircular indentations are

semicircular in cross section, but are semicylindrical in three dimensions. The sheet material is thus shaped so that the recesses when assembled define a plurality of compartments, each extending partially around one of the conductors so as to enclose a substantial portion thereof, such that the conductors 12 are separated from each other by the cusp regions 35, 36 forming portions of the casing which extend in-between the conductors. The upper housing 16 and the lower housing 17 made from light gauge galvanised steel. The conductors 10, 1 1, 12 are coated in polyamide, glass fibre and resin 12' insulation to insulate the conductors from each other and the housing. A further layer of ceramic paper may also be provided for this purpose. The tabs 27 and 37 of the upper housing and lower housing are welded continuously along the length of the housing. Tabs 28 and 38 are similarly welded. The conductors are now hermetically sealed from the outside environment (the conductors and housing will be terminated in a conventional sealed manner). Referring to figure 2, the housing may be further strengthened and the conductors further secured by being squeezed together and then spot welding opposing cups regions 25, 35 and 26, 36 on the upper housing 16 and a lower housing 17.

The housing and cable are both self supporting, and together are strong enough to support a powered tool as it is lowered down the production tube. The strength of the cable and housing may be easily increased by providing a thicker diameter cable and/or a thicker housing. Also, since the conductors and the housing are both made of copper clad steel, they will have the same rate of thermal expansion, and avoiding internal forces due to differential expansion that can damage the cable and/or housing, and rupture the insulation creating short circuits.

In alternative embodiments, the copper clad steel sheet material of the housing may be formed as a circular or other cross section tubular shape which encloses the group of copper clad steel conductors without extending in-between them so as to define compartments.

In another alternative embodiment, the sheet material of the housing 16, 17 may be made from plastics material, and the conductors 12 may be made from copper. Referring to figure 3, here the housing 40 is a single piece of galvanised steel, having six semicircular indentations 41, 42, 43, 44, 45, 46 formed along the width of the housing. Semicircular indentations 43, 44 adjoin with no separation, however, the other adjacent semicircular indentations are separated from each other by spacer regions 47, 48, 49, 50. Both ends of the housing 40 has a flat tab region 51, 52. Referring to figure 4, the housing 40 is bent over so that the material deforms at the point between the semicircular indentations 43, 44, so conductor 10 is encompassed by semicircular indentation pair 41, 46, conductor 11 by semicircular indentation pair 42, 45 and conductor 12 by semicircular indentation pair 43, 44. Further, spacer regions 47 and 50, spacer regions 48 and 49, and flat tab regions 51, 52 all abut. To secure the conductors in housing, the flat tab regions 51, 52 are welded along the length of the housing, sealing the conductors against the outside environment. Spacer regions 47 and 50 and spacer regions 48 and 49 may be spot welded at points to further secure the conductors in the housing. It will be seen that the spacer regions of this embodiment separates the conductors 10, 11, 12 at little more than the cusp regions of the embodiments shown in figures 1 and 2.

Referring to figure 5, a housing has six semicircular indentations 61, 62, 63, 64, 65, 66. Conductors 10, 11, 12 are initially disposed in semicircular indentations 62, 63, 64.

The pair of semicircular indentations 61, 62 and the pair 64, 65 adjoin with no separation, whereas semicircular indentations 62, 63, 64 are separated from each other by cusp regions 66, 67 and the pair of semicircular indentations 61, 62 by cusp region 68. The housing section has a flat tab 71, 72 at each end.

Referring to figure 6, the housing the bent over so that the material deforms at the point between the semicircular indentations 61 , 62 and at the point between the semicircular indentations 64, 65. As in a similar manner to previous embodiment, deforming the material in this way causes the conductors 10, 11, 12 to be encompassed between semicircular indentation pair 61, 62, pair 63, 66, and pair 64, 65 respectively. The flat tabs 71, 72 meet in the region between power conductors 10 and 11, and are angled so that when they meet, their surfaces abut one other. The flat tabs are welded along the edge of the housing to hermetically seal the conductors. Referring to figure 7, the flat tabs 71, 72, now welded, have their joined edge trimmed off, and are pressed in towards the region between conductors 10 and 11. Having the weld located down between conductors 10 and

1 1 means that the weld is more protected than in the previous embodiments, because the weld is shielded by the conductors 10 and 1 1 and the housing around them.

Referring to figure 8, again a single-piece housing has six indentations 81, 82, 83, 84, 85, 86, but indentation 81 describes three-quarters of a circle whilst

indentation 86 describes only a quarter of a circle. In this arrangement, when the housing is bent over the conductors, flat tabs 87, 88 meet at point above conductor 10 in the figure rather than between conductors 10 and 11 as for the previous embodiment. In this case, after the flat tabs 87, 88 have been welded along their length, the welded seam may be bent over shown in figure 9, so that less of a protuberance is exposed (lessening the chances of the weld being knocked and so deformed.)

Referring to figures 10 and 11, if the flat tabs 92, 93, 94, 95 are made sufficiently long, the housing 90, 91 can be sealed by a fold and seal crimping process similar to that used to hermetically seal tin can joints. In this example, conductors 10, 11,

12 are disposed between upper and lower housing 90, 91, with flat tab pairs 92, 93 and 94, 95 being sealed in this manner; however, the single piece housings having a single seam to be joined can also be secured together and sealed in this manner. In the embodiments so far described, the conductors have been arranged in a flat relationship. They may though be arranged in a 'round' or triangularly packed relationship in order to provide a cable system with a smaller maximum diameter, which can be very useful in downhole use the available diameter may be limited. Referring to figure 12, conductors 10, 11, 12 are placed between upper and lower housing portions 100, 101, the conductors being encompassed between the upper housing's semicircular indentations 102, 103, 104, and the lower housing's semicircular indentations 105, 106, 107. Both housings include spacer regions 110, 111, 112, 113 between the semicircular indentations. In this embodiment though the spacer regions 112, 113 are comparatively long. Referring to figure 13, after the flat tabs 108, 109 and the flat tabs 114, 115 have been welded together, spacer regions 112, 113 are deformed using rollers so that conductor 12 comes to rest in the region between conductors 10 and 11. Thus, the conductors with the housing take on a triangularly stacked (clustered) relationship wherein their respective central longitudinal axes do not lie in a common plane.

Referring to figure 14, in an alternative arrangement, a housing initially has a single circular indentation 120, and two rounded arms 121, 122 which each end in tabs 123, 124 angled from the arms. Firstly, circular indentation 120 is formed around a first conductor 10. Referring to figure 15, secondly, two further conductors 11, 12 are placed in the rounded arms 121, 122 which are deformed around the conductors until, referring to figure 16, the rounded arms encompass the conductors 1 1, 12 and the tabs 123, 124 abut along their length. The tabs 123, 124 are then continuously welded along the length of the housing to hermetically seal the conductors 10, 1 1, 12. These operations can all be performed by passing the housing and conductors through a series of rollers. Referring to figure 17, individual conductors 10 may be individually sealed within a housing 130. An upper housing 137 has a single semicircular indentation 131, a long flat tab 132 and a short flat tab 133. A lower housing 138 is a similar shape to the upper housing, also having a single semicircular indentation 134, a long flat tab 136 and a short flat tab 135. The upper and lower housing 137, 138 is arranged around the conductor 10. Since the lower housing is oriented upside down to the upper housing, the long flat tab 132 of the upper housing 137 abuts the short flat tab 135 of the lower housing 137, and the short flat tab 132 of the upper housing 137 abuts the long flat tab 136 of the lower housing 137, as shown. Both pairs of abutting tabs are continuously welded along the length of the conductors to hermetically seal it from the outer environment.

It will be noted that the welded seams of the housing of a conductor so clad each has one tab overlapping and extend from the other tab. Referring to figure 18, individual conductors 10, 11, 12 are clad with upper and lower housings 137, 138, 147, 148, 157, 158 respectively. The overlapping weld formed from the short tab 133 of upper housing 137 and the long tab 136 of the lower housing 138 interlocks with the overlapping weld formed from the long tab 142 of upper housing 147 and the short tab 145 of the lower housing 148, to form a half lap splice joint. A similar joint is formed between the short tab 143 of upper housing 147, the long tab 146 of the lower housing 148 and the long tab 152 of upper housing 157 and the short tab 155 of the lower housing 158. These half lap splice joints can then be continuously or spot welded to secure the individually clad conductors 10, 11, 12 together in a flat assembly. It will be seen that a row of as many conductors so clad can be joined together in this manner as desired, and that each conductor so clad can be rotated 180° and the overlapping weld will still overlap in the correct fashion to join with other similarly clad conductors.

Referring to figure 19, three conductors 10, 11, 12 in a housing 15 may be simply be disposed in production tubing 39 in order to suspend a tool such as a motor as it is lowered through the production tubing, and to supply power to the tool. The conductors and housing may take all or the majority of the weight of the tool.

Alternatively, referring to figure 20, the conductors 10, 11, 12 and housing 15 may be banded to the outside of the coiled tubing 39, a tool being suspended on the coiled tubing which is lowered down the well. Housing 15 is deformed slightly so that the conductors 10, 11, 12 lie in a slightly curved arrangement against the curvature of the outside of the tubing. The conductors 10, 11, 12 and housing 15 could also be curved to fit against the inner surface of the tubing.

In alternative embodiments, the adjoining edges of the sheet material of the casing may be inward facing towards the conductors so that they can be joined for example by resistance welding or fillet welding to leave a smooth seam. It will be understood that sheet material means material in flat and relatively thin form, which will generally be supplied as an elongate strip, e.g. on a roll.

In summary, preferred embodiments provide a cable for use in hydrocarbon wells which is manufactured by forming an impervious sheet material to define a plurality of recesses, introducing each of two or more conductors into a respective one of the recesses, and folding the sheet material and joining two edges thereof to form a seam. The recesses form compartments, each enclosing a substantial portion of a respective conductor, so that the conductors are separated from each other by portions of the casing which extend in-between the conductors.

In alternative embodiments, the casing can be made from plastics sheet material, or both the sheet material of the casing and the conductors may be made from copper clad steel so as to avoid differential thermal expansion, in which case the casing may simply enclose the bundled conductors without separating them into compartments. Fig. 21 illustrates this construction, wherein the casing 21 1 is made from plastics sheet material with the conductors 212 of copper, or the casing 211 and individually insulated conductors 212 are made from from copper clad steel, and the casing is seamed at a fillet weld 213. In each of the above described embodiments, each of the conductors is enclosed in an individual insulating jacket which defines its outer circumference.

Where the casing is made from plastics material, the conductors may be made from copper clad steel, so that the cable is self supporting even at great depths. Where the conductors are made from copper, the cable may be supported for example by attaching it to or frictionally engaging it with production tubing or continuous (coiled) tubing or by floating it in a fluid within continuous (coiled) tubing, whereby the casing may enclose a void or buoyancy material for that purpose. Metal cased cable may similarly be made self supporting by providing copper clad steel conductors, or may be supported buoyantly or by attachment to or frictional engagement with production tubing or continuous (coiled) tubing. The metal casing can be made from steel, copper clad steel, aluminium or other metals. Many further adaptations will be evident to those skilled in the art.

Claims

1. A cable for use in a hydrocarbon well or borehole, comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being substantially impervious to hydrocarbon wellbore fluids; wherein the outer casing is made from sheet material and is shaped to define a plurality of compartments, each extending partially around one of the conductors so as to enclose a substantial portion thereof, such that the conductors are separated from each other by portions of the casing which extend in-between the conductors.

2. A cable for use in a hydrocarbon well or borehole, comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being substantially impervious to hydrocarbon wellbore fluids; wherein the outer casing is made from plastics sheet material.

3. A cable according to claim 1 or claim 2, wherein the sheet material is welded so as to join two edges thereof at a seam which extends longitudinally along the cable.

4. A cable according to claim 1, wherein the sheet material is metal.

5. A cable according to claim 4, wherein two edge portions of the sheet material are joined by crimping or folding so as to form a seam which extends longitudinally along the cable.

6. A cable according to claim 1, wherein both the sheet material and the conductors are made from steel with a copper cladding.

7. A cable according to any previous claim and comprising at least three said conductors.

8. A cable according to claim 7 wherein the conductors are arranged in parallel, side by side configuration such that respective central longitudinal axes of all of the cables lie in a common plane.

9. A cable according to claim 7 wherein the conductors are arranged in a clustered configuration such that respective central longitudinal axes of all of the cables do not lie in a common plane.

10. A cable for use in a hydrocarbon well or borehole, comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being substantially impervious to hydrocarbon wellbore fluids; wherein the outer casing is made from sheet material, and both the sheet material and the conductors are made from steel with a copper cladding.

1 1. A method of manufacturing a cable for use in a hydrocarbon well or borehole, the cable comprising at least two conductors, each conductor surrounded by insulation, and an outer casing that encloses the conductors and defines an outer surface of the cable, the outer casing being made from sheet material and substantially impervious to hydrocarbon wellbore fluids; comprising the steps of a) fonriing the sheet material to define a plurality of recesses, b) introducing each of the conductors into a respective one of the recesses, and c) folding the sheet material and joining two edges thereof to form a seam, such that the recesses form compartments, each compartment enclosing a substantial portion of a respective conductor, such that the conductors are separated from each other by portions of the casing which extend in-between the conductors.

12. A method according to claim 7, wherein the casing is folded after joining the two edges thereof so as to arrange the conductors in a desired configuration.