CABLE ARRANGEMENT

Abstract: The present invention relates to a cable, particularly for monitoring and/or controlling oil/gas wells, comprising a protective tube (6; 16) of metal, reinforced synthetic material or the like, said protective tube surrounding at least one fiber tube (3; 13), said fiber tube containing at least one optical fiber (4; 14), wherein the cable comprises organs for venting the cable.

Description: Cable arrangement The present invention relates to a cable according to the preamble of claim 1. In the field of monitoring and/or controlling oil/gas wells, a cable may be positioned within or attached to the outside of the tubing. The cable extends from the wellhead to various communication nodes, sensors and actuators down hole. Cables of this kind must be able to withstand high temperatures, large hydrostatic pressures and an aggressive environment. In addition, the cable must withstand large mechanical pressures . Experience has shown that cables comprising an optical element, preferably optical fibers, are susceptible to attack by hydrogen from the surrounding environment, the hydrogen penetrating into the optical element, causing an attenuation increase and resulting in communication failure. Therefore, the optical element must be protected against in-diffusion of hydrogen. In the prior art this has been done according to at least one the following solutions: choosing fibers comprising glass materials which are insensitive to hydrogen in-diffusion, Use of a barrier of for example metal or carbon outside the fiber, so-called hermetic fibers, Use of specific materials, e.g. hydrogen scavenging greases, which capture/tie up free hydrogen, Using tube enclosures of metal or plastic that act as barriers preventing or delaying in-diffusion of hydro- gen . The present invention aims at protecting the optical element against the in-diffusion of hydrogen, possibly in combination with one or more of the above mentioned tech- niques . This aim is reached by means of a cable according to the characterizing clause of claim 1. Further features and ad- vantages are mentioned in the dependent claims and the following description, by reference to the drawings, where: fig. 1 shows a section of a cable according to a first em- bodiment of the present invention, fig. 2 shows a section of a cable according to a second embodiment of the present invention, fig. 3 shows a section of a cable according to a third embodiment of the present invention, fig. 4 shows a section of a cable according to a fourth embodiment of the present invention, and fig. 5 shows a section of a cable according to a fifth embodiment of the present invention. Fig. 1 shows a section of a cable comprising a metal core 1 provided with at least one groove 2 for the positioning of various elements . These elements may comprise at least one optical fiber 4 and/or insulated conductor 5. The groove 2 may in addition to positioning of various ele- ments be used for venting, either by using the groove 2 directly, or by positioning a separate tube in the groove. The cable comprises a protective tube 6 of metal, reinforced synthetic material or the like. Fig. 2 shows a section of a cable corresponding to the one in fig. 1, which in addition is provided with a sheath 7 comprising a temperature and chemically resistant polymer. Fig. 3 shows a section of a cable with a stranded core. The core is build up around a central element 11, around which at least one tube 18 is stranded, the tube providing the cable venting organ. The central element 11 may be hollow and thereby also provide a venting organ, possibly in combination with said tube 18. The core comprises at least one tension element 12, in addition to at least one fiber element 13, which is provided with at least one fiber 14. The tension element 12 and the fiber element 13 are stranded in the same way as the venting organ. A protective tube 16 of metal, reinforced synthetic material or the like is provided around the core. Fig. 4 shows a section of a cable with a stranded core corresponding to the cable in fig. 3, comprising at least one insulated conductor 18. Fig. 5 shows a section of a cable corresponding to the ca- bles in fig. 3 and 4, the outside of the tube 16 of protective metal, reinforced synthetic material or the like being provided with a sheath 17 of temperature and chemically resistant polymer. This construction, comprising at least one gas filled cavity between the outer tube 6, 16 or the outer sheath 7, 17 and the central cable elements 1, 3, 5, 11, 12, 13, 18, enables transport of hydrogen before it diffuses into the cable elements comprising optical fiber 4, 14. Hydrogen is a light gas that will rise upwards without active help, i.e. passively. Another solution is to vent out the hydrogen by pumping a suitable gas, e.g. nitrogen, through at least one insulated cavity 8, 18, the gas being led down to the bottom of the cable and thereafter displacing the unwanted gas in the cavity. The introduced gas rises through the cable between the core elements and vents out the hydrogen by pushing it upwards to the top of the cable (surface) . It is understood that the present invention easily may be used in combination with other techniques that prevent in- diffusion of hydrogen, such as use of barriers of metal, carbon or grease. It is also understood that a skilled person by means of the specification, claims and/or drawings may conceive of various modifications and changes without departing from the scope and spirit of the present invention.

Claims: C l a i m s 1. A cable, particularly for monitoring and/or controlling oil/gas wells, comprising a protective tube (6; 16) of metal, reinforced synthetic material or the like, said protective tube surrounding at least one fiber tube (3; 13), said fiber tube containing at least one optical fiber (4; 14), c h a r a c t e r i z e d i n that the cable comprises organs for venting the cable . 2. A cable according to claim 1, c h a r a c t e r i z e d i n that at least one venting tube (18) is stranded around a central element (11) . 3. A cable according to claim 1 or 2 , c h a r a c t e r i z e d i n that the central element (11) comprises a hollow channel which provides a venting organ, said central hollow element possibly being used in combination with said venting tubes (18) . 4. A cable according to claim 2 or 3 , c h a r a c t e r i z e d i n that at least one fiber tube (13) , possibly one or more insulated conductors (15) and one or more tension elements (12) , are stranded around the central element (11) , said central element (11) possibly comprising a hollow channel, said hollow channel possibly being used in combination with one or more venting tubes (18) , said fiber tube (13) comprising at least one fiber (14) . 5. A cable according to claim 1, c h a r a c t e r i z e d i n that the venting organs are formed in a central element (1) , said central element (1) extending out towards the protective tube (6) , said venting organs being provided in the form of at least one groove (2) , preferably adjacent to the protective tube (6) . 6. A cable according to claim 5, c h a r a c t e r i z e d i n that a tube (8) forming a venting organ is positioned in said at least one groove (2) . 7. A cable according to claim 5 or 6 , c h a r a c t e r i z e d i n that the central element (1) is provided with enough grooves (2) to constitute or receive at least one venting organ and receive at least one fiber tube (3) , said at least one fiber tube (3) comprising at least one optical fiber (4) , the central element (1) comprising a material able to withstand tension and pres- sure . 8. A cable according to one of the previous claims, c h a r a c t e r i z e d i n that the protective tube (6; 16) is covered by a sheath (7; 15) comprising a tem- perature and chemically resistant polymer. 9. A cable according to one of the previous claims, c h a r a c t e r i z e d i n that it is used in combination with other methods for preventing in-diffusion of hydrogen . 10. A cable according to one of the previous claims, c h a r a c t e r i z e d i n that the venting is passive. 11. A cable according to one of the previous claims, c h a r a c t e r i z e d i n that the venting is active .

Inventors: KRISTENSEN RUNE, NESSET EIVIND, KRISTENSEN, RUNE, NESSET, EIVIND
Applicants: ABB KRAFT AS, KRISTENSEN RUNE, NESSET EIVIND, KRISTENSEN, RUNE, NESSET, EIVIND
Application year: 1999
Main classification: H01B7
IPC codes: E21B17, G02B6