GB2173034A - Oil well logging cable - Google Patents

Abstract

An oil well logging cable comprises a telecommunication part concentrically arranged within a power cable part, and armouring 8. The telecommunication part comprises insulated conductors 1, 2 arranged in star quad formation or optical fibres and the power cable part comprises flat insulated conductors 20, 21 or circular conductors (5, 10 Figs. 1 & 3). Heat resistant textile tape or braid 7 is provided between the flat wires 8 and the power conductors 20. Plastics filler strings (6, Fig. 1) may be used between the conductors. The conductors 1 may comprise a central insulating filament (4, Fig. 2). <IMAGE>

Description

SPECIFICATION Oil well logging cable This invention relates to cables and in particular to cables for logging oil wells, so called oil well logging cables. Such cables are used to lower test equipment into the oil wells. They also represent a communication link between the test equipment in one end of the cable and surface-based equipment in the other end of the cable. Electrical power is supplied to the test gear via the cable. The cable concerned must be long enough to be used in offshore oil wells which may be as deep as 2000-5000 metres. The cable may in some cases be as long as 6000 metres.

The cable must be capable of withstanding tough- environmental conditions. Temperatures exceeding 200"C are npt rare and the exposure of the cable to hot oil and driiling mud must be carefully considered. The resistance against longitudinal strain and surface abrasion should be high, because the cable must be strong enough to be reused several times.

The cable should futhermore be light and have a relatively small diameter.

Experiments have beem made with an oil well logging cable comprising seven insulated copper conductors. Six conductors were stranded in a layer around the seventh, centre, conductor. Over the bundle of conductors there was wound a layer of heat-resistant tape. The purpose of this layer was to keep the conductors together and to provide a bedding for an outer armouring. In such a cable the armouring consisted of two layers of round or circular steel wires which were applied as cross armouring. There was used steel with relatively high break strength. The cross wound armour did to a large extent withstand torsion, but this problem was not considered to be of great importance.

Four of the seven conductors constituted two communication pairs for transferring signals between the test gear in the drilling well and the surface equipment. Two of the outer conductors (numbers 5 and 6) were used for supplying power to the test gear while the seventh conductor was held in reserve. Signals from the surface to the test gear were applied via a phantom circuit, i.e. two and two of the communication conductors were connected in parallel. The four communication conductors were therefore used as mentioned for transmitting signals in both directions.

At least two problems were experienced with the just-mentioned cable: -the crosstalk and noise were high on all three signals circuits (the two pairs and the phantom circuit), -when the cable was pulled up and down, its round wire armouring had a sawing effect which led to grooves in the walls of the well.

This problem is serious when the well has bends and deviates from a straight line because the cable may get struck in the grooves and break.

A main object of the present invention is to provide an oil well logging cable which does not experience the drawbacks of the abovementioned cable.

According to the invention in its broadest aspect, there is provided an oil well logging cable comprising a telecommunication part, a power part and armouring, characterised in that the telecommunication part of the cable is arranged fully within a concentric power cable part and armouring.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 illustrates the crossection of one embodiment of the invention, Figure 2 shows the crossection of one of the conductors, Figures 3-5 show alternative embodiments of the invention, and Figures 6-8 show alternative embodiments of the power conductors.

In order to solve the crosstalk and noise problems in the three signal circuits the four conductors may be arranged as a star quad, and this star quad should be arranged in the centre of the cable. This is illustrated in Fig. 1 where four wires 1, which are provided with individual layers of insulation 2, are stranded into a quad configuration. The dimension of the conductor insulation may easily be defined so as to give the star quad excellent characteristics for the phantom circuit as well as for the two symmetrical pair circuits. The wire 1 may as illustrated in Fig. 2, be of the multifilament type where six wires 3 are stranded around a centre wire 4. The centre wire 4 may be replaced by an insulation filament to avoid kinking effects.The conductor insulation should be of a type which maintains high mechanical strength at temperatures up to at least 250 . Polytetrafluorethylene (PTFE) and polymers under trade names Peek, Ultem, Datex and Tefcel may be suitable.

Returning to Fig. 1, two power conductors 5 are stranded around the communication cable core to constitute a concentric layer. Filler elements 6 may be introduced to fill up the concentric layer.The filler elements or strings may be made of the same insulation material as the conductor insulation or other synthetic material such as Kevlar fibres.

Over the power conductor layer 5, 6 there is placed a covering of heat-resistant material 7. This covering may consist of one or more overlapping windings of a tape of textile material. A braid may also be used, and alternatively layers of Kevlar fibres.

In the preferred embodiment of the invention the round armouring wires are replaced by one or more, preferably two layers of flat wires 8. The armouring wires should be so dimensioned as to be placed close together, particularly the wires of the outermost layer.

Thereby there is obtained a more smooth cable surface and the cable diameter is kept to a minimum.

By using flat armour elements in or or more layers the abrasion surface of the cable is substantially increased. The problem of making grooves in the oi! well walls is thereby greatly reduced. - Furthermore the cable itself will be stronger and it will survive a greater number of loggings. The armour should preferably have the form of a cross armour, i.e. two flat armour layers wound on top of each other with opposite direction of lay. If the communication part of the cable contains one or more optical fibres the length of lay of the armour should be as long as practically possible In order to keep the cable dimensions within acceptable limits, each of the power conductors (5, Fig. 1) may be constituted by two or more conductors 10 arranged in parallel as illustrated in Fig. 3.The number of conductors 10 should be even, e.g. ten so that five and five of the conductors 10 can be connected in parallel.

Alternatively each power conductor may be constituted by a number of wires 15 which are in longitudinal contact with each other as indicated in Fig. 4, within a common insulation 16. In Fig. 4 three and three of these power conductors could be connected in parallel at the two ends of the cable i.e. at the surface side and at the- test gear side. The telecommunication part is represented by a star quad 17.

In Fig. 5 is illustrated a cable having a teltecommunication quad as described and four flat or tape-like power cable conductors 20 with insulation 21. The conductor 20 may be constituted by a copper tape (30, Fig. 6) which is corrugated within a sheath of insulation material 31.

In the embodiment shown in Fig. 4 the wires could be undulated in-phase as shown in Fig. 7 or out-of-phase as shown in Fig. 8.

The alternative embodiments of the cable and conductors are not shown to scale.

The embodiments of Figs. 4-5 are preferred to the embodiments of Figs. 1 and 3 because a circular small cross-section is more readily obtainable with these embodiments.

The telecommunication part may in all embodiments of the cable be a quad as described or it may be constituted by one or more optical fibres.

The power cable part should preferably be symmetrical with filler elements arranged in between the power conductors, if necessary, to make up a full layer.

Claims (11)

1. Oil well logging cable comprising a telelcommunication part, a power part and armouring, characterised in that the telecommunication part of the cable is arranged fully within a concentric power cable part and armouring.

2. Cable according to claim 1, characterised in that the telecommunication part consists of a star quad (1,2).

3. Cable according to claim 1, characterised in that the telecommunication part consists of one or more optical fibres.

4. Cable according to claim 1, characterised in that the concentric power cable part is costituted by at least two power conductors (5, 10, 15, 20), possibly with filler elements (6), to make up a complete layer.

5. Cable according to claim 4, characterised in that the power conductors have a flat configuration (10; 15, 16; 20, 21).

6. Cable according to claim 5, characterised in that each of the power conductors are subdivided into a number of individualiy insulated conductors.

7. Cable according to claim 5 or 6, characterised in that each of the power conductors is constituted by at least one insulated, preferably corrugated, copper tape (30).

8. Cable according to claim 5 or 6, characterised in that each of the power conductors or subconductors is constituted by a number of parallelly arranged wires arranged within common insulation.

9. Cable according to claim 8, characterised in that the wires (32, 34) are undulated within the common insulation (33, 35).

10. Cable according to claim 1, characterised in that the armouring is constituted by one or more layers of flat armouring elements (8).

11. Oil well logging cable substantially as described with reference to the accompanying drawings.