GB2329487A - Combined optic fibre/electrical well logging cable - Google Patents

Abstract

A combination fiber optic/electrical well logging cable 10 comprises at least one insulated electrical conductor 9 and a plurality of armor wires 6 surrounding the electrical conductor 9. The armor wires 6 include at least one tube 4A having an optical fiber disposed inside the tube. The armor wires 6 may be in two concentric layers circumscribing the electrical conductor. One or more of the armor wires 6 in the innermost layer of armor wires may includes the tube 4A having the optical fiber disposed therein. The tube may have an external diameter which is substantially the same as the armor wires in the layer in which the tube is located. The inner diameter of the tube may provide just enough room for the optical fiber to move about freely, but to retain enough crush strength for the tensile and side loads expected to be applied to the cable. The tube may include an inner layer consisting of a thin walled tube, a metal foil layer wrapped around the outside of the inner layer, and an outer layer consisting of another thin walled tube on the outside of the foil layer.

Description

is 2329487 WELL LOGGING CABLES The invention relates to armored cables

used in well logging. More specifically, the invention relates to well logging cables which include one or more optical fibers for communicating data and/or control signals between the earth's surface and well logging instruments attached to one end of the logging cable.

Electrical well logging cables typically include one or more insulated electrical conductors surrounded by a plurality of steel armor wires which provide the cable with tensile strength and abrasion resistance. The electrical conductors transmit electrical power to well logging instruments attached to one end of the cable, and transmit data and/or control signals between equipment located at the earth's surface and the well logging instruments.

Some well logging instruments transmit signal data at such high rates that using electrical conductors for such data transmission is difficult. When using such well logging instruments it is desirable to use optical fibers to carry optical data telemetry because optical telemetry typically has much greater data transmission rate capability than does electrical telemetry. The well logging instruments using optical data telemetry preferably should receive electrical power from the earth's surface over the logging cable just as do electrical telemetry logging instruments, so a logging cable including a combination of electrical conductors and optical fibers is desirable. Several types of combination fiber optic/electrical cable are known in the art. A sales brochure entitled 11Electro-Optical Mechanical Umbilicals,' published by Vector Cable Company, Sugar Land, Tex. (publication date unknown) shows several configurations for an electrical cable including both optical fibers and electrical conductors surrounded by steel armor wires. The cables disclosed is surrounded by steel armor wires. The cables disclosed in the Vector Cable Company brochure, however, are typically 2/3 of an inch or more in external diameter, making them impracticable for use as a well logging cable. Typical well logging cables do not exceed about 17/32 inch external diameter. This is mainly because of space limitations on the typical well logging surface instrumentation system, and as known in the art is also related to the use of certain wireline wellbore pressure control equipment the use of which is made more difficult to use as the diameter of the logging cable is increased.

Another type of combination optical fiber/electrical cable is disclosed in U. S. patent no. 4,697,875 issued to Priaroggia. The cable disclosed in the Priaroggia '875 patent is entirely unsuitable for use as a well logging cable because the electrical conductors are disposed externally to a wire rope strength member, and are covered externally with a plastic jacket. As is well known in the art of well logging, the typical well logging cable should have an abrasion resistant material such as steel on the outside.

other combination fiber optic/electrical well logging cables are disclosed in U. S. patent no. 4,696,542 issued to Thompson and U. S. patent no. 4,522,464 issued to Thompson et al. The cables disclosed in these patents have limitations to their use as well logging cables which are well documented in U. S. patent no. 5,495,547 issued to Rafie et al and assigned to the assignee of this invention. More specifically, the cables disclosed in the Thompson 1542 and Thompson et al '464 patents do not have, to the greatest extent possible, the electrical and mechanical characteristics of well logging cables which have only electrical conductors. Having such electrical and mechanical properties is desirable in a well logging cable to enable use of such logging cables in situations where the logging instruments attached to the cable only include electrical telemetry, thus avoiding the need to have different types of cable available for each type of instrument telemetry system.

The Rafie et al 1547 patent discloses several configurations for a combination fiber optic/electrical well logging cable which retain the preferred electrical and mechanical characteristics of conventional well logging cables which have only electrical conductors. The cables disclosed by Rafie et al 1547 however, require expensive and difficult to use connection devices to make the electrical and optical connections to the well logging instruments attached to the end of the cable. What is needed is a combination fiber optic/electrical well logging cable which retains the electrical and mechanical characteristics of a conventional electrical well logging cable having only electrical conductors, and includes the capability of electrical and mechanical connection to the well logging instruments using conventional electrical/mechanical connection techniques.

Various aspects of the present invention are exemplified by the attached claims.

An embodiment of the invention can provide a combination fiber optic/electrical well logging cable. The cable includes at least one insulated electrical conductor and a plurality of armor wires surrounding the electrical conductor. In one embodiment of the invention, the cable includes seven insulated electrical conductors arranged in a regular hexagonal pattern. The armor wires include at least one tube having an optical fiber disposed inside the tube. In a preferred embodiment of the invention, the armor wires is are disposed in two concentric layers circumscribing the electrical conductors. One or more of the armor wires in the inner layer of armor wires includes the tube having the optical fiber disposed therein.

The tube has an external diameter which is substantially the same as the armor wires in the layer in which the tube is located. The inner diameter of the tube is selected to provide just enough room for the optical fiber to move about freely, but to retain enough crush strength for the tensile and side loads expected to be applied to the cable.

In a particular embodiment of the invention, the tube includes an inner layer consisting of a thin walled tube, a metal foil layer wrapped around the outside of the inner layer, and an outer layer consisting of another thin walled tube on the outside of the foil layer. The metal foil layer substantially fills the annular space between the inner layer and the outer layer so that the tube behaves mechanically similarly to a solid tube having the same internal and external diameters.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a cross-section through a well logging cable embodying the invention.

Figure 2 shows steel tubes having optical fibers therein used in substitution of one or more of the inner and/or outer armor wires of the logging cable shown in Figure 1.

Figure 3 shows an alternative design for the steel tubes shown in Figure 2 wherein the tube consists of an inner layer, a foil layer and an outer layer.

A cross-section of a combination fiber optic/electrical well logging cable according to the -S- is invention is shown at 10 in Figure 1. The logging cable 10 includes a central conductor bundle 2. The central bundle 2 for the cable 10 shown in Figure 1 includes seven insulated electrical conductors 9 arranged in a regular hexagonal pattern. Each one of the electrical conductors 9 can be formed from stranded copper wires 12 surrounded by an insulating sheath 8 made of plastic or other suitable electrically insulating, flexible material. Typical dimensions for the conductors 9 are disclosed, for example, in a product catalog published by Camesa, Inc., Rosenberg, Tex., listing the construction of each of the conductors 9 as including seven stranded copper wires each one 0.0128 inch diameter, surrounded by a 0.084 inch insulating sheath made from polypropylene or ITEFZELTm11 (trade name of a copolymer made by E. I.

DuPont de Nemours & Co.). Void spaces 14 between the conductors 9 within the hexagonal pattern can be filled with a suitable plastic insulating material well known in the art.

It is to be clearly understood that the configuration of the central bundle 2 shown in Figure 1 is only an example and is not meant to limit the invention to seven insulated conductors 9. Other acceptable configurations for the central bundle 2 are well known in the art and can include a different number of, or different sizes of electrical conductors.

For example, certain smaller diameter well logging cables well known in the art include a central bundle consisting of only one insulated electrical conductor.

Other well logging cables include three or four insulated electrical conductors in the central bundle 2.

An alternative design to the stranded copper conductors shown in the Camesa, Inc. catalog is disclosed, for example, in U. S. patent no. 5,495,547 is issued to Rafie et al. The alternative electrical conductor 9 can include a copper covered steel wire about 0.027 inches in diameter surrounded by nine copper wires each about 0.0128 inches in diameter, these all being surrounded by an insulating jacket of about 0.084 inches in diameter. This configuration for the alternative electrical conductor is shown at Figure 3 in the Rafie et al 1547 patent.

Either type of electrical conductor 9 as just described herein can be electrically connected to well logging instruments (not shown) by using sealed electrical connectors well known in the art.

once again referring to Figure 1, the central bundle 2 is typically surrounded by two concentric layers of steel armor wires. The armor wires 4, 6 can also be formed from corrosionresistant alloy such as one known by trade designation MP-35N where the logging cable is intended to be used in wellbores having corrosive fluids therein. The armor wires include inner armor wires shown at 4 forming the innermost concentric layer. For the cable 10 shown in Figure 1, the inner armor wires 4 can include eighteen steel wires each having an external diameter of about 0. 047 inches. The inner armor wires 4 are themselves typically surrounded by an outer layer of armor wires 6. For the cable shown in Figure 1, the outer armor wires 6 can include eighteen steel wires each having an external diameter of about 0.066 inches. It is to be clearly understood that other numbers of, diameters of, and number of layers of armor wires can be used with this invention consistent with minimizing the external diameter of the cable 10 and at the same time providing commercially acceptable breaking strength of the cable 10. The numbers, diameters of and numbers of layers of the armor wires shown in Figure 1 are meant only to serve as an example of a suitable configuration and are not meant to limit the invention.

In an embodiment of the invention, one or more of the inner armor wires 4, such as the one shown at 4A, can consist of a steel tube having an optical fiber disposed therein, as will be further explained. Alternatively, or in addition to the tube shown at 4A, one or more of the outer armor wires 6, such as the one shown at 6A, can consist of a steel tube having an optical fiber disposed therein, as will be further explained. If the armor wires 4, 6 are formed from a corrosion resistant alloy, such as the previously described MP-35N, then the tubes, 4A, 6A should be formed from the same or similar material to provide the desired corrosion resistance.

The tube 4A which substitutes for one of the inner armor wires 4 is shown in more detail in Figure 2. This tube 4A should have an external diameter substantially the same as the external diameter of the inner armor wires 4 so that symmetry of the layer of armor wires is maintained. In this example, the outer diameter of the tube 4A can therefore be about 0.047 inches. An optical fiber 16 disposed inside the tube 4A can be of types known in the art. The fiber 16 shown in this example has an external diameter of about 0.007 inches. The internal diameter of the tube 4A in this example is about 0.023 inches. The internal diameter of the tube 4A should be selected to provide enough space for the optical fiber 16 to move about f reely inside the tube 4A, but should also be no more than that which is reasonably needed for the optical fiber 16, so that the tube 4A will have sufficient strength to resist crushing under tensile and side loading which is likely to be applied to the cable (10 in Figure 1). Methods for calculating a maximum internal diameter of the tube 4A which will allow for the maximum expected tensile and side loading on the logging cable 10 are known in the art, including finite element analysis as can be performed using a computer program sold under the trade name 11ANSYS11 by Southpoint, 275 Technology Dr., Canonsburg, PA.

As previously explained, one or more of the outer armor wires (6 in Figure 1) may also consist of a steel tube 6A (or corrosion resistant alloy tube as previously explained) inside which is disposed an optical fiber 18. In the example in Figure 2, the tube 6A can have an external diameter of 0.066 inches and an internal diameter of about 0.023 inches to accommodate the optical fiber 18. The external and internal diameters of the tube 6A should be selected to satisfy substantially the same mechanical criteria as the tube 4A substituting one of the inner armor wires (4 in Figure 1). It should be noted that substitution of one or more of the outer armor wires (6 in Figure 1) by the tube 6A may be less desirable than substituting one or more of the inner armor wires (4 in Figure 1) with the tube 4A, from the standpoint of possibility of failure of the tube 6A due to wear in its outer surface by abrasion with continued use. The example of the tube 6A is intended primarily to show that the invention is not to be limited in scope to substitution of inner armor wires 4 by the tube 4A.

Figure 3 shows a different design for the tube 4B which is intended to facilitate splicing of the well logging cable at any intermediate position along its length, while maintaining the hydraulic integrity of the tube 4B so that fluid under very high pressure, as is typically present in a wellbore, may be excluded from the inside of the tube 4B.

The tube 4B consists of an outer layer 20, a metal foil layer 22 and an inner layer 24. The optical fiber 16 is disposed within the inside of the inner layer 24 just as it is in the first embodiment of this is invention.

The outer layer 20 can be a thin walled tube, which in this example can have an external diameter of about 0.047 inches and an internal diameter of about 0.037 inches. The external diameter of the outer layer 20 is selected in this example for the case where the tube 4B will be included within the inner layer of armor wires on the cable (shown in Figure 1 at 10). The outer layer 20 could also have an external diameter about the same as that of the armor wires in the outer layer of armor (6 in Figure 1) if that is where the tube is to be located. The outer layer 20 can be made from steel or the corrosion resistant alloy such as MP35N used for any of the other armor wires (4 in Figure 1) in the cable.

The inner layer 24 can also be formed from thin walled tube. In this example, the inner layer 24 has an internal diameter of about 0.020 inches and an external diameter of about 0.028 inches. The internal diameter of the inner layer 24 should be large enough to enable the fiber 16 to move about freely, but be no larger than that needed to maintain sufficient crush resistance and tensile strength of the tube 4B, just as is the case for the first embodiment of the tube (4A in Figure 2) in this invention. The inner layer 24 can be made from the same material as the outer layer 20, but this is not necessary to construction of the tube 4B.

The annular space between the inner layer 24 and the outer layer 20 can be filled with a metal foil 22 wrapped in a helical pattern around the outside of the inner layer 24. The thickness of the metal foil 22 should be about the same as the width of the annular space between the inner layer 24 and the outer layer 20. Since the annular space between the outer layer 20 and the inner layer 24 is substantially filled by the metal foil 22, the tube 4B will have nearly the same is crush strength as that of the solid-construction tube (4A in Figure 2) in the first embodiment of the invention.

It is contemplated that where the logging cable (10 in Figure 1) must be spliced, the fiber 16 may be coupled using techniques known in the art. The inner layer 24 may be coupled using a thin walled steel sleeve (not shown) which fits over the outside of the inner layer 24 and can be welded or otherwise coupled to exclude entry of fluid under high pressure from entering the inside of the inner layer. The metal foil 22 may be substituted by compressible material such as plastic, or can be omitted, over the interval in which the sleeve (not shown) is located. Then the outer layer 20 may be joined by butt welding or similar to provide mechanical coupling between the joined ends across the splice.

The tube 4B in Figure 3 has about the same internal and external diameter as the solidconstruction tube (4A in Figure 2) and retains substantially the same mechanical properties of the solid-construction tube (4A in Figure 2), but is better adapted to maintain hydraulic integrity across a splice than is the solid-construction tube MA in Figure 2).

Those skilled in the art will devise other embodiments of this invention which do not depart from the spirit of the invention as disclosed herein.

Claims (10)

1. A combination f iber optic/electrical well logging cable, comprising:

at least one insulated electrical conductor; and a plurality of armor wires surrounding said at least one electrical conductor, said armor wires comprising at least one tube having an optical fiber disposed therein.

2. A well logging cable as claimed in claim 1, wherein said armor wires are disposed in a plurality of substantially concentric layers surrounding said at least one electrical conductor, said at least one tube having an external diameter substantially the same as an external diameter of other ones of said armor wires disposed in a same one of said concentric layers.

3. A well logging cable as claimed in claim 2, wherein said at least one tube has an internal diameter selected to provide free movement of said optical fiber therein and to provide sufficient strength for tensile and side loads applied to said well logging cable.

4. A well logging cable as claimed in claim 2, wherein said tube is disposed within an innermost one of said plurality of concentric layers.

5. A well logging cable as claimed in any one of claims 1 to 4, wherein said armor wires comprise steel.

6. A well logging cable as claimed in any one of claims 1 to 5, wherein said armor wires comprise a corrosion resistant alloy.

7. A well logging cable as claimed in claim 1, wherein said at least one tube comprises an inner layer, a metal foil layer disposed on an outer surface of said inner layer, and an outer layer disposed on an outside surface of said metal foil layer.

8. A well logging cable as claimed in claim 7, wherein said armor wires are disposed in a plurality of substantially concentric layers surrounding said at least one electrical conductor, and said outer layer has an external diameter substantially the same as an external diameter of other ones of said armor wires disposed in the same one of said concentric layers.

9. A well logging cable as claimed in claim 7, wherein said inner layer has an internal diameter selected to provide free movement of said optical fiber therein and to provide sufficient crush strength for tensile and side loads applied to said well logging cable.

is

10. A well logging cable substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.