FIBRE SPOOLING APPARATUS

Abstract

An apparatus and method for deploying an elongate medium in a bore is described. The apparatus includes a housing defining an internal spool cavity, and the housing is configured to be deployed in the bore. A spool of elongate medium is mounted within the spool cavity. The housing defines an outlet to permit the elongate medium to be deployed from the spool cavity, and an inlet to permit bore fluid to enter the housing during deployment of the elongate medium from the spool cavity. In use, the housing includes an isolating fluid to isolate the elongate medium from the bore fluid entering the housing. Also described is a kit for deploying elongate medium in a bore and a method of preparing an apparatus for deployment of an elongate medium in a bore.

Claims

1. An apparatus for deploying an elongate medium in a bore, comprising: a housing defining an internal spool cavity and configured to be deployed in the bore; and a spool of elongate medium mounted within the spool cavity; wherein the housing defines an outlet to permit the elongate medium to be deployed from the spool cavity, and an inlet to permit bore fluid to enter the housing during deployment of the elongate medium from the spool cavity; and wherein, in use, the housing comprises an isolating fluid to isolate the elongate medium from the bore fluid entering the housing.

2. The apparatus of claim 1, configured such that the spool of elongate medium remains isolated from bore fluid which has entered the cavity during complete deployment of the elongate medium from the spool cavity.

3. The apparatus of claim 1, wherein the internal spool cavity defines a vacant space not occupied by the spool of elongate medium, wherein, in use, the vacant space is at least partially filled with the isolating fluid, and wherein the vacant space is dimensioned such that during deployment of the elongate medium, the elongate medium remains isolated from bore fluid which has entered the cavity.

4. The apparatus of claim 1, wherein the inlet is positioned to permit bore fluid to enter into the housing relative to the spool cavity such that, in use, an interface is established between the isolating fluid and bore fluid entering the spool cavity, the interface advancing along the spool cavity as the elongate medium is deployed, and wherein the spool of elongate medium is provided to be maintained in a non-contact relationship with the advancing interface.

5. The apparatus of claim 1, wherein the housing is configured to prevent bore fluid from entering the internal spool cavity above a flow rate determined in accordance with a rate of deployment of the elongate medium.

6. The apparatus of claim 3, wherein the spool of elongate medium is configured such that the rate of deployment of the elongate medium provides a volumetric increase of the vacant space equal to the rate of intake of bore fluid.

7. The apparatus of claim 1, wherein the vacant space defined by the internal spool cavity is, in use, partially or completely filled with isolating fluid and partially filled with a gas.

8. (canceled)

9. The apparatus of claim 4, wherein the spool of elongate medium is configured to be deployed such that the volume of the cavity occupied by the spool of elongate medium decreases from one end of the spool cavity to the other to maintain the spool of elongate medium in the non-contact relationship with the advancing interface.

10. The apparatus of claim 1, wherein the internal spool cavity comprises a first chamber and a second chamber, the spool of elongate medium being mounted within the first chamber, and wherein the first and second chambers are configured to be in fluid communication to permit, in use, isolating fluid provided in the second chamber to be received within the first chamber to fill the volume within the first chamber which has been vacated by the deployed elongate medium.

11. The apparatus of claim 10, wherein the volume of the second chamber is at least equal to the volume vacated by the elongate medium in the first chamber when the elongate medium is fully deployed.

12. The apparatus of claim 10, wherein the internal spool cavity is provided with a partition between the first and second chambers, configured to provide a flow path from the second chamber to the first chamber.

13. The apparatus of claim 10, comprising a filter provided between the first chamber and the second chamber.

14. The apparatus of claim 1, wherein the outlet is provided with a one-way valve permitting a flow path from the spool cavity to the bore or wherein the inlet is provided with a one-way valve permitting a flow path from the bore into the housing.

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

19. A method for deploying an elongate medium in a bore, comprising: deploying an apparatus comprising a housing defining an internal spool cavity and a spool of elongate medium mounted within the internal spool cavity, and wherein the housing comprises an isolating fluid, in a bore; deploying an elongate medium from an outlet of the housing; and receiving bore fluid via an inlet of the housing, as the elongate medium is deployed through the outlet.

20. The method of claim 19, wherein the volume of bore fluid received corresponds to the volume vacated by the deployed elongate medium.

21. The method of claim 19, comprising isolating the spool of elongate medium from the bore fluid entering the cavity during the complete deployment of the elongate medium.

22. The method of claim 19, wherein an interface is defined between the isolating fluid and the bore fluid entering the spool cavity, and the method comprising maintaining the spool of elongate medium in a non-contact relationship with the interface during deployment of the elongate medium.

23. The method of claim 21, comprising deploying the elongate medium such that the volume occupied by the spool of elongate medium decreases from one end of the spool cavity to the other to maintain the spool of elongate medium in the non-contact relationship with the interface.

24. The method of claim 19, wherein the internal spool cavity comprises a first chamber and a second chamber, the spool of elongate medium being mounted within the first chamber, and wherein the first and second chambers are configured to be in fluid communication, the method comprising: permitting isolating fluid provided in the second chamber to be received within the first chamber to fill the volume within the first chamber which has been vacated by the deployed elongate medium.

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. A kit for deploying an elongate medium in a bore, the kit comprising: an apparatus configured to be deployable in a bore, the apparatus comprising a housing defining an internal spool cavity, an outlet and an inlet; and a spool of elongate medium mounted within the spool cavity, and a fluid tank, wherein the fluid tank is configured to contain a volume of an isolating fluid.

33. (canceled)

34. (canceled)

35. (canceled)

36. (canceled)

37. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0125] These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying figures, in which:

[0126] FIGS. 1a to 1d are diagrammatic illustrations of an apparatus according to the present disclosure in use in a wellbore;

[0127] FIGS. 2a to 2d are diagrammatic illustrations of the apparatus of FIGS. 1a to 1d in use in a wellbore having a portion of gas;

[0128] FIGS. 3a to 3d are diagrammatic illustrations of an alternative apparatus according to the present disclosure in use a wellbore;

[0129] FIGS. 4a to 4d are diagrammatic illustrations of the alternative apparatus of FIGS. 3a to 3d in use in a wellbore having a portion of gas;

[0130] FIGS. 5a to 5d are diagrammatic illustrations of the apparatus of FIGS. 1a to 1d inside a lubricator stack prior to deployment;

[0131] FIGS. 6a and 6b are diagrammatic illustrations of the apparatus of FIGS. 1a to 1d inside a lubricator stack prior to deployment;

[0132] FIGS. 7a to 7f illustrate a method of winding an elongate medium on a bobbin;

[0133] FIGS. 8a to 8c are diagrammatic illustrations of a further alternative apparatus according to the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0134] Aspects of the present disclosure relate to the deployment of an elongate medium in a wellbore, such as an oil and/or gas wellbore. In particular, an apparatus for deploying an elongate medium in a bore configured such that an elongate medium may be deployed from the apparatus as the apparatus traverses through a bore. Elongate media, such as optical fibres, can be damaged or compromised and the deployment process can be hindered by exposure to environmental conditions in the bore; in particular, drilling mud (e.g., oil and/or water based drilling mud) which has been weighted with ground barium powder has been shown to cause damage to optical fibres. The apparatus may be configured to reduce the risk of damage to the elongate medium and/or hindering of the deployment process, for example, by preventing fluid from the bore entering the portion of the apparatus containing the elongate medium, or by reducing the exposure of the elongate medium in the apparatus to bore fluid. Of course, the apparatus may be used in many applications or environments, and may be used to deploy any type of elongate medium where the same advantages may be realised.

[0135] With reference to FIGS. 1a to 1d, there are shown diagrammatic illustrations of an example apparatus 10 according to the present disclosure.

[0136] FIG. 1a illustrates the apparatus 10 prior to deployment. The apparatus 10 comprises a housing 20, including an internal spool cavity 11, an inlet 13 and an outlet 18. The apparatus 10 defines a leading end 50 and a trailing end 52, the leading end 50 being substantially aligned with and facing the direction of travel of the apparatus 10 in use. The inlet 13 is provided at the leading end 50 of the apparatus 10, and the outlet 18 is provided at the trailing end 52 of the apparatus 10. Immediately before deployment, the apparatus 10 may be orientated above a wellbore 12 with its leading end substantially aligned with and facing its intended direction of travel.

[0137] The internal spool cavity 11 includes an elongate medium 16 wound around a spool or bobbin 17. The elongate medium 16 may be used during or after deployment for multiple applications. In some examples, the elongate medium 16 may be used for communication and/or distributed sensing within the wellbore 12, such as distributed temperate sensing (DTS), distributed pressure sensing (DPS), distributed acoustic sensing (DAS), or the like.

[0138] The cavity 11 is configured to contain an isolating fluid 41. The isolating fluid 41 may comprise any fluid, in particular, any liquid. The isolating fluid 41 may be selected in accordance with the application in which the apparatus 10 is used. In some examples, the isolating fluid may be selected to have a particular density and/or viscosity. In some examples, the isolating fluid 41 may comprise clean bore fluid (such as unused bore fluid or previously used and cleaned bore fluid). The bore fluid may comprise a completion fluid, or the like. In other examples, the isolating fluid 41 may comprise a water-based fluid, or cesium formate, or a mixture thereof.

[0139] Prior to deployment, as shown in FIG. 1a, the cavity 11 is completely filled with an isolating fluid 41. The cavity 11 is arranged to surround the elongate medium 16 within the housing 20. In one example, the isolating fluid 41 may comprise clean bore fluid, such as that discussed above. Using bore fluid may ensure that the density of the isolating fluid 41 is sufficient such that the apparatus 10 continually moves downwards through the bore fluid 42 within the wellbore 10 during deployment of the elongate medium 16. That is, the apparatus 10 may have a negative buoyancy when deployed.

[0140] As shown in FIG. 1a, the elongate medium 16 is connected to a surface device 21, which may include a transmitter and/or receiver. The surface device 21 may be located at the surface, however the device 21 may be located equally downhole at a point along a wellbore.

[0141] FIG. 1b illustrates the apparatus 10 in use at a first stage of deployment in a wellbore 12. As the apparatus 10 traverses the wellbore 12, the elongate medium 16 is deployed from the outlet 18 as it unspools from the bobbin 17. Consequently, the volume of elongate medium 16 occupying the cavity 11 is reduced as the elongate medium 16 is deployed. In this example, such deployment of the elongate medium 16 results in the isolating fluid 41 moving towards the outlet 18 as it fills the space vacated by the deployed elongate medium 16, as indicated generally by arrow 14. Concurrently, bore fluid 42 from the wellbore enters the cavity 11 via the inlet 13, as indicated generally by arrow 19. Such movement of the isolating fluid 41 and bore fluid 42 may provide for the apparatus 10 to be pressure compensated as the apparatus 10 traverses the wellbore 12 and the elongate medium 16 is deployed.

[0142] As bore fluid 42 enters the cavity 11, a fluid-fluid interface 43 is established between the isolating fluid 41 and the bore fluid 42. Such an interface may be achieved by selecting an isolating fluid 41 that is immiscible with the bore fluid 42. Alternatively, this may be achieved by selecting an isolating fluid 41 with sufficient viscosity such that mixing with bore fluid is prevented or minimised; however, the isolating fluid 41 should not be so viscous that it inhibits proper unspooling of the elongate medium 16. The apparatus 10 may be configured to traverse the wellbore 12 such that agitation and/or turbulence of the apparatus 10, and therefore fluid within the cavity 11, may be eliminated or minimised. For example, this may be achieved by configuring the apparatus 10 such that it is streamlined as it traverses the wellbore 12. For example, this may be particularly desirable where the isolating fluid 41 comprises bore fluid. In this instance, the isolating fluid 41 may have similar properties to the bore fluid 42 entering the apparatus 10. As such, the bore fluid 42 may be capable of mixing with the isolating fluid 41, which would thereby break the interface 43. Configuring the apparatus 10 to traverse the wellbore 12 such that agitation and/or turbulence is eliminated or minimised may assist to ensure the interface 43 is maintained throughout the entire deployment of the elongate medium 16.

[0143] In one example, the volume of bore fluid 42 entering the cavity 11 via the inlet 13 may be equal to the volume within the cavity 11 that has been vacated by the deployed elongate medium 16. However, in other examples, a portion of the isolating fluid 41 may be vacated alongside the elongate medium 16 as it is deployed, for example, due to the boundary layer effect. In this respect, the volume of bore fluid 42 entering the cavity 11 may be equal to the volume within the housing 20 that has been vacated by the deployed elongate medium 16 and isolating fluid 41.

[0144] FIG. 1c illustrates the apparatus 10 at a second stage of deployment in the wellbore 12. At this stage, the apparatus 10 has traversed further into the wellbore 12 and more of the elongate medium 16 has been deployed. Consequently, a larger volume of elongate medium 16 has vacated the cavity 11, and a larger volume of bore fluid 42 has entered the cavity 11. As such, the interface 43 has advanced within the housing 20 towards the outlet 18. The elongate medium 16 is configured such that it depletes from one end of the bobbin 17 to the other, starting at the end of the bobbin 17 closest to the inlet 13 of the apparatus 10. As illustrated in this example, the apparatus 10 is configured such that the interface 43 is maintained at a distance from the spool of the elongate medium 16. Therefore, the spool of elongate medium 16 and bore fluid 42 remain in a non-contact relationship throughout the deployment of the elongate medium 16.

[0145] FIG. 1d illustrates the apparatus 10 at a third stage of deployment in the wellbore 12. At this stage, the apparatus 10 has traversed further into the wellbore 12, and all of the elongate medium 16 has been deployed. Consequently, a larger volume of elongate medium 16 has vacated the cavity 11, and a larger volume of bore fluid 42 has entered the cavity 11. As such, the interface 43 has advanced further within the housing 20 towards the outlet 18; however, the bobbin 17 and interface 43 remain separated in this example, being spaced apart by a distance D1, such that the bobbin 17 and elongate medium 16 remain in a non-contact relationship with the advancing interface 43 throughout the entire deployment of the elongate medium 16.

[0146] The apparatus 10 of the present example may provide for the elongate medium 16 within the cavity 11 to be protected from damaging exposure to bore fluid 42 during deployment thereof.

[0147] Although not illustrated in the Figures, the use of the apparatus 10 may involve any number of subsequent stages, which, for example, may involve abandonment or retrieval of the apparatus 10 and/or elongate medium 16. In some examples, the elongate medium 16 may be used for distributed sensing within the wellbore 12, such as distributed temperate sensing (DTS), distributed pressure sensing (DPS), distributed acoustic sensing (DAS), or the like. The apparatus 10 may be provided with an on-board electrical system, which, for example, may be used for communication.

[0148] The previous example illustrates the apparatus 10 in use in a wellbore that is full of bore fluid comprising only a liquid portion. However, in other examples, the apparatus 10 may be used in a wellbore that also comprises a portion of gas, for example, a gas cap above the liquid portion. When the apparatus 10 is used in such a wellbore, the elongate medium 116 is deployed through two different environments; initially the gas portion followed by the liquid portion. During deployment of the elongate medium 16 through the gas portion of the wellbore, the apparatus 10 may experience a significantly smaller drag force than when compared to traversing the liquid portion. As such, the velocity at which the apparatus 10 traverses the gas portion may be substantially greater than that when in the liquid portion. Therefore, the rate of deployment of the elongate medium 16 from the cavity 11 may be substantially greater in the gas portion.

[0149] Without wishing to be bound by theory, the present inventor has discerned that such an increase in velocity of the apparatus, and thus an increase in the rate of deployment of the elongate medium, through the gas portion of the wellbore may have an adverse effect on the interaction between the unspooling elongate medium and the isolating fluid. For example, the increased rate of the unspooling of the elongate medium may impart on an isolating fluid within the cavity an increased rotational velocity. Such an increase in rotational velocity of the isolating fluid may cause vortices to form, which may result in cavitation of the isolating fluid. Such a scenario may be detrimental to the deployment of the elongate medium and/or the structural integrity of the apparatus.

[0150] FIGS. 2a to 2d illustrate the apparatus 10 of FIGS. 1a to 1d being used in connection with a wellbore 60 having bore fluid 42 comprising a liquid portion 47 as well as a gas portion 44. In this example, the gas portion 44 is a gas cap.

[0151] FIG. 2a illustrates the apparatus 10 prior to deployment. As with the previous examples, the apparatus 10 comprises a housing 20, including an internal spool cavity 11, an inlet 13 and an outlet 18. The internal spool cavity 11 is configured to contain an isolating fluid 41 and an elongate medium 16 wound around a bobbin 17. Furthermore, the elongate medium 16 extends through the outlet of the apparatus to connect to a surface device 21.

[0152] In this example, the cavity 11 is only partially filled with an isolating fluid 41 prior to deployment. As shown in FIG. 2a, the cavity 11 is approximately 50% filled with isolating fluid 41 from the leading end 50 of the apparatus 10; however, this is not essential. In other examples, the cavity may be less than 50% full, such as 15% full, 25% full, etc., or more than 50% full, such as 75% full, 85% full, etc. The remaining volume of the cavity 11 at the trailing end 52 of the apparatus 10 is filled with a gas 46, which in this example is air.

[0153] FIG. 2b illustrates the apparatus 10 at a first stage of deployment in the gas portion 44 of the wellbore, which is a gas cap. The gas portion 44 is separated from the liquid portion 47 by a gas-fluid interface 48 within the wellbore 60. As with the previous example, the elongate medium 16 is deployed from the outlet 18 as the apparatus 10 traverses the wellbore 60. As such, the volume of elongate medium 16 occupying the cavity 11 is reduced. However, as shown in FIG. 2b, the isolating fluid 41 remains substantially in its initial configuration. At this stage, the apparatus 10 has not yet entered the liquid portion 47 of the wellbore 60, and as such, no bore fluid 42 has entered the cavity 11 to drive the isolating fluid 41 towards the outlet 18. Hence, this allows for the elongate medium 16 within the cavity 11 to be substantially surrounded by gas 46, rather than isolating fluid 41, during the increased rate of deployment and unspooling of the elongate medium 16. Such an arrangement may reduce the likelihood of adverse interactions of the unspooling elongate medium in a liquid isolating medium. This may provide for a smooth, reliable deployment of the elongate medium without the risk of damage to the structural integrity of the apparatus 10.

[0154] FIG. 2c illustrates the apparatus 10 at a second stage of deployment. At this stage, the apparatus 10 has traversed further into the wellbore 60 and is below the interface 48, submerged in the liquid portion 47 of the wellbore 60. As shown in FIG. 2c, bore fluid 42 from the liquid portion 47 of the wellbore 60 now enters the cavity 11 via the inlet 13, as indicated generally by arrow 19, thus establishing the fluid-fluid interface 43. Furthermore, as bore fluid 42 enters the cavity 11 the isolating fluid 41 moves towards the outlet 18, as indicated generally by arrow 14. This causes the gas 46 within the cavity 11 to be displaced out of the cavity 11 and into the wellbore 60 via outlet 18, as illustrated by the formation of bubbles 58 in the bore fluid 42 of the wellbore 60.

[0155] FIG. 2d illustrates the apparatus 10 at a third stage of deployment. At this stage, the apparatus 10 has traversed further into the wellbore 12 and all of the elongate medium 16 has been deployed. As shown in FIG. 2d, the interface 43 has advanced further within the cavity 11 such that all of the gas 46 has been displaced therefrom. It will be appreciated, however, that the gas 46 will be fully displaced from the cavity 11 shortly after the apparatus 10 enters the liquid portion 47 of the wellbore 60, and thus well before the illustrated third stage of deployment in FIG. 2d. At this stage, immediately after the gas 46 has been fully displaced from the cavity 11, the spool of elongate medium 16 would become fully immersed in isolating fluid 41.

[0156] The skilled person will appreciate that the apparatus of FIGS. 2a to 2d will function in the same way regardless of the location of the gas-fluid interface 48 in the wellbore 60. Indeed, the apparatus of FIGS. 2a to 2d may also be used in a wellbore comprising bore fluid 42 having only a liquid portion, for example, like the wellbore 12 of FIGS. 1a to 1d. In this instance, upon deployment of the apparatus 10, bore fluid 42 from the wellbore would immediately enter the cavity 11 via the inlet 13, the gas 46 would immediately displace from the cavity 11, and the apparatus 10 would thereafter function in the same way as the apparatus of FIGS. 1a to 1d.

[0157] Referring to FIGS. 3a to 3d, there are shown diagrammatic illustrations of an alternative apparatus of FIGS. 1a to 1d. The alternative apparatus of FIGS. 3a to 3d is similar in many respects to the apparatus of FIGS. 1a to 1d, and therefore like features are denoted by like numerals incremented by 100.

[0158] In this alternative apparatus, the axial length of the bobbin 117 is greater than the axial length of the bobbin 17 of FIGS. 1a to 1d. In this example, the apparatus 110 is used in connection with a wellbore 120 comprising bore fluid 142 that consists only of liquid, and not gas. As such, the cavity 111 has been completely filled with isolating fluid 141 prior to deployment. The bobbin 117 and elongate medium 116 occupy substantially more of the volume of the cavity 111 in this arrangement, and thus the vacant space 115 in the cavity 111 is less. As such, the isolating fluid required to fill the cavity 111 is less than that required to fill the cavity 11 of the apparatus of FIGS. 1a to 1d.

[0159] The elongate medium 116 is deployed from the outlet 118 as the apparatus 110 traverses the wellbore 112. The volume of elongate medium 116 occupying the cavity 111 is thereby reduced, and bore fluid 142 from the wellbore 120 enters the cavity 111 via the inlet 113, such that pressure is balanced throughout the apparatus 110. Again, an interface 143 is established between the isolating fluid 141 and the bore fluid 142, which advances through the cavity 111 as the elongate medium 116 is deployed.

[0160] In this example, the spool of elongate medium 116 is configured such that it depletes from one end of the bobbin 117 to the other. As such, the interface 143 may remain positioned relative to the elongate medium 116 such that as the elongate medium 116 is deployed, the elongate medium 116 within the cavity 111 is immersed in isolating fluid 141, and isolated from bore fluid 142. As shown, a distance D2 is maintained between the elongate medium 116 within the cavity 111 and the advancing interface 143 as the elongate medium 116 is deployed. The distance D2 may vary as the elongate medium 116 is deployed, but should never reach zero so as to avoid bore fluid 142 contacting the elongate medium 116. This may be achieved by the manner in which the elongate medium 116 is mounted or wound on the bobbin 117. For example, the elongate medium 116 may be mounted on the bobbin 117 such that the elongate medium 116 depletes in an axial direction away from the advancing interface 143.

[0161] FIGS. 4a to 4d illustrate the apparatus 110 of FIGS. 3a to 3d where the cavity has been partially filled with isolating fluid 141. FIG. 4a illustrates the apparatus 110 prior to deployment. In this example, the apparatus 110 is used in a wellbore having bore fluid 142 comprising a liquid portion 147 and a gas portion 144, much like the wellbore 60 of FIGS. 2a to 2d. As such, the cavity 111 has been filled partially with an isolating fluid 141. In this example, the isolating fluid 141 occupies less of the cavity 111 than that of the isolating fluid 41 in the cavity 11 of FIGS. 2a to 2d. However, it should be understood that any volume of isolating fluid 141 may be selected that is sufficient to sustain the interface 143 between the isolating fluid 141 and bore fluid 142 entering the cavity 111, such that the spool of elongate medium 116 remains isolated from the bore fluid 142 during deployment of the elongate medium 116.

[0162] FIG. 4b illustrates the apparatus 110 at a first stage of deployment in a wellbore 160. In this example, the wellbore 160 consists of a liquid portion 147 and a gas portion 144 separated by a gas-fluid interface 148; however, such a filling process would enable the apparatus 110 to be used equally in a wellbore consisting only of a liquid portion, much like the wellbore 120 of FIGS. 3b to 3d. In such a scenario, upon deployment of the apparatus 110, bore fluid 142 from the wellbore would immediately enter the cavity 111 via the inlet 113, the gas 146 would immediately displace from the cavity 111, and the apparatus 110 would thereafter function in the same way as the apparatus 110 of FIGS. 3a to 3d.

[0163] As with the previous examples, the elongate medium 116 is deployed from the outlet 118 as the apparatus 110 traverses the wellbore 160. As such, the volume of elongate medium 116 occupying the cavity 111 is reduced. However, as shown in FIG. 4b, the isolating fluid 141 remains substantially in its initial configuration. At this stage, the apparatus 110 has not yet entered the liquid portion 147 of the wellbore 160, and as such, no bore fluid 142 has entered the cavity 111 to drive the isolating fluid 141 towards the outlet 118. Hence, this allows for the elongate medium 116 within the cavity 111 to be substantially surrounded by gas 146, rather than isolating fluid 141, during the increased rate of deployment and unspooling of the elongate medium 116. Such an arrangement may reduce the likelihood of adverse interactions of the unspooling elongate medium in a liquid isolating medium. This may provide for a smooth, reliable deployment of the elongate medium without the risk of damage to the structural integrity of the apparatus 110.

[0164] FIG. 4c illustrates the apparatus 110 at a second stage of deployment. At this stage, the apparatus 110 has traversed further into the wellbore 160 and is below the interface 148, submerged in the liquid portion 147 of the wellbore 160. As shown in FIG. 4c, bore fluid 142 from the liquid portion 147 of the wellbore 160 now enters the cavity 111 via the inlet 113, as indicated generally by arrow 119, thus establishing the fluid-fluid interface 143. Furthermore, as bore fluid 142 enters the cavity 111 the isolating fluid 141 moves towards the outlet 118, as indicated generally by arrow 114. This causes the gas 146 within the cavity 111 to be displaced out of the cavity 111 and into the wellbore 160 via outlet 118, as illustrated by the formation of bubbles 158 in the bore fluid 142 of the wellbore 160.

[0165] FIG. 4d illustrates the apparatus 110 at a third stage of deployment. At this stage, the apparatus 110 has traversed further into the wellbore 160 and all of the elongate medium 116 has been deployed. As shown in FIG. 4d, the interface 143 has advanced further within the cavity 111 such that all of the gas 146 has been displaced therefrom. It will be appreciated, however, that the gas 146 will be fully displaced from the cavity 111 shortly after the apparatus 110 enters the liquid portion 147 of the wellbore 160, and thus well before the illustrated third stage of deployment in FIG. 4d.

[0166] FIGS. 5a to 5d illustrate an example of the apparatus 10 of FIGS. 1a to 1d used in connection with a lubricator stack 100. The lubricator stack 100 sits on top of the wellbore 12 and blowout preventer (BOP) 102, and in this example, the bore fluid of the wellbore 12 comprises only a liquid portion 47. The elongate medium 16 extends from the apparatus 10 through the lubricator stack 100 to a surface device 21.

[0167] The apparatus 10 is initially provided in an unfilled condition inside the lubricator stack 100, prior to deployment in the wellbore 12. FIG. 5b illustrates the lubricator stack 100 being pressure tested. During the pressure test, the lubricator stack 100 is filled with a pressurised fluid 104, which in this example is achieved by pumping fluid 104 through valve 106. The movement of fluid 104 through the lubricator stack 100 is indicated generally by arrows 101. The inflow of fluid 104 results in an increase in pressure in the lubricator stack 100, as indicated by pressure sensor 103. As the fluid 104 beings to fill the lubricator stack 100, the fluid 104 enters the apparatus 10 via the inlet 13. In this example, the pressurised fluid 104 has been selected so that it may also suitably function as the isolating fluid 41 of the apparatus 10. The inlet 13 of the apparatus 10 is provided with a one-way valve 112, which permits fluid to enter the cavity 11 and prevents fluid from exiting the cavity 11. As such, this provides for the cavity 11 to be filled with isolating fluid 41 through the inlet 13 while also being able to retain the isolating fluid 41 in the cavity 11 thereafter.

[0168] Once the pressure test is complete, the fluid 104 is removed from the lubricator stack 100, as shown in FIG. 5c. The apparatus 10 however remains completely full of fluid 104 by virtue of the one-way valve 112. As noted, the fluid 104 used in the pressure test has been selected to function also as the isolating fluid 41 of the apparatus 10. Therefore, at this stage, the apparatus 10 is ready for deployment in the wellbore 12. FIG. 5d illustrates the lubricator stack 100 open to the wellbore 12, which has resulted in an increase in pressure shown by pressure sensor 103, and as shown, the apparatus 10 now exits the lubricator stack 100 to enter the wellbore 12 and start deployment of the elongate medium 16.

[0169] While the example of FIGS. 5a to 5d show the apparatus being completely filled with isolating fluid prior to deployment, this may not necessarily be the case. For example, the apparatus may be used in connection with a lubricator stack on top of a wellbore comprising a liquid portion as well as a gas portion; for example, much like the wellbore 60 of FIGS. 2b to 2d. Where the apparatus is used in such a wellbore, it may be required that the apparatus is partially filled with isolating fluid and partially filled with gas prior to deployment.

[0170] FIG. 6a illustrates the apparatus 10 inside the lubricator stack 100 after the pressure test has been completed. In this example, the apparatus 10 comprises a draining mechanism 200. The draining mechanism 200 may be configured to drain partially the isolating fluid 41 from the cavity 11 of the apparatus 10. As such, this may provide for the apparatus 10 to be partially filled with isolating fluid 41 and partially filled with gas 46 prior to deployment, much like the example apparatus of FIGS. 2a to 2d. This configuration allows for the apparatus 10 to be used in a wellbore comprising a liquid portion and a gas portion, such as a gas cap.

[0171] The draining mechanism 200 is provided on a side face of the housing 20 and positioned approximately halfway between the leading end 50 and trailing end 52 of the apparatus 10. In other examples, however, the draining mechanism 200 may be positioned more or less than halfway between the leading end 50 and trailing end 52.

[0172] FIG. 6b illustrates the apparatus 10 exiting the lubricator stack 100 and entering the gas cap 44 of the wellbore 60.

[0173] With reference to FIGS. 7a-7f, there is shown a winding process which may be used where the elongate medium 16 is wound onto a bobbin 17. Here, the elongate medium is wound in a first axial direction, indicated by arrow 62, relative to a bobbin axis 40 to form a number of adjacent individual turns or wraps, at a steep winding pitch which provides the adjacent wraps in contact with each other (i.e., a closed winding pitch). In the present case the first axial direction is such that the elongate medium 16 is added to the bobbin in an upslope direction of a conical portion 38, starting at point 61 and ending at point 64, thus defining a first wrap layer 66. By winding in an upslope direction each wrap or turn provides support to the subsequent wound wrap or turn of the elongate medium 16.

[0174] As shown in FIG. 7b, the elongate medium is then wound in a reverse second axial direction, illustrated by arrow 68, over the first wrap layer 66 at a much shallower winding pitch, until reaching point 70 where the elongate medium 16 is on the cylindrical portion 36 of the winding surface adjacent the starting point of the first wrap layer 66. This may form a first portion 72 of a second wrap layer 74. Following this, as shown in FIG. 7c, winding of the elongate medium 16 is continued further in the second axial direction, illustrated by arrow 76, to form a second portion 78 of the second wrap layer 74, until reaching point 80. The second portion 78 of the second wrap layer 74 is wound at a steeper winding pitch (in this case a closed winding pitch) relative to the first portion 72 of the second wrap layer 74. The second portion 78 may function to provide support to the first wrap layer, and as such in some cases the second portion 78 may be defined as an anchor or anchor winding portion. The first and second wrap layers 66, 74 may form a first wrap segment 82.

[0175] Following this, as illustrated in FIG. 7d, the elongate medium 16 is wound again in the first direction, illustrated by arrow 84, over the first wrap segment 82, at a closed wind pitch until reaching point 86 to form a subsequent first layer 88. Next, as illustrated in FIG. 7e, the elongate medium 16 is wound in the direction of arrow 90, at a shallower winding pitch over the first layer 88 until reaching point 92, with the elongate medium 16 continuing to be wound in the direction of arrow 94 in FIG. 7f to complete a second wrap layer 96. The newly formed first and second wrap layers 88, 96 define a second wrap segment 98 which axially overlaps the first wrap segment 88, wherein each wrap segment extends to a common outer diameter.

[0176] The winding process may be continued in the same manner to add further axially overlapping wrap segments each with first and second wrap layers, distributed along the length of the bobbin 17. The winding process may be continued until the required length of elongate medium 16 has been wound onto the bobbin 17 to form a complete spool. In some examples between 10 to 10,000 meters, and possibly more, of elongate medium may be wound onto the bobbin 17, perhaps over 2 to 300, and possibly more, axially overlapping wrap segments.

[0177] The provision of partially overlapping wrap segments may be such that at least a proportion of one wrap segment is supported or constrained by the overlapping adjacent segment. Further, the multiple adjacent and overlapping segments may provide a degree of resistance to being disturbed by any object, such as the unspooled portion of the fibre, dragging thereacross. Also, the supporting effect of the overlapping segments may be such that any requirement for end flanges may be minimised or eliminated.

[0178] FIGS. 8a to 8c illustrates a further alternative apparatus 310 in accordance with the present disclosure. The apparatus 310 may comprise a housing 320 having a first chamber 322 and a second chamber 324. In this particular example, the first and second chambers 322, 324 are in fluid communication with a filter 332 provided in the flow path 326. Where the filter 332 is provided, the filter acts as an additional means to prevent debris from bore fluid 342 entering the first chamber 322.

[0179] The elongate medium, which in this example is optical fibre, is mounted within the first chamber 322. The elongate medium is wound round bobbin 317 which is then subsequently mounted into the first chamber 322, although one will appreciate that the bobbin 317 is not necessarily required for the elongate medium to be mounted in the first chamber 322. For clarity, the elongate medium is not shown in FIGS. 8a to 8c.

[0180] In use, the apparatus 310 is filled with isolating fluid 341 such that the isolating fluid 341 occupies the free volume in both the first and second chambers 322, 324, as shown in FIG. 8a. One method of filling the apparatus 310 with isolating fluid 341 is to submerge the apparatus 310 in a volume of isolating fluid 341 such that the isolating fluid 341 enters via fluid inlet 328, whilst any gas or fluid initially present inside the chambers 322, 324, for example air, is expelled via outlet 318. The apparatus may be submerged in a tank containing the volume of isolating fluid. The isolating fluid 341 may be immiscible with the bore fluid 342. In this example, the isolating fluid 341 may be at least one of the following: a water-based fluid, an oil-based fluid, a mixture of water-based and oil-based fluid. The isolating fluid may be water, or cesium formate, or a mixture thereof.

[0181] Filling the apparatus 310 with isolating fluid 341 may occur at the deployment site, for example at the surface of a wellbore. Alternatively, the apparatus may be delivered to the deployment site pre-filled with isolating fluid.

[0182] The apparatus 310 is then deployed into the wellbore and the elongate medium deployed into a second configuration. The second configuration may be such that the elongate medium provides one or more coiled portions in the wellbore. A coiled portion need not be helically wound, per se, but rather any bundle of elongate medium that could otherwise serve to provide increased resistance/sensitivity compared to other portions of the elongate medium.

[0183] A first end of the elongate medium may be anchored to a surface, for example to a surface module such that the elongate medium is deployed as the apparatus traverses the wellbore. The apparatus 10 may be deployed via gravity, however, it should be understood that other methods of deployment may be employed such as, for example, via fluid pumping or a combination thereof. Fluid pumping may be employed, for example, in deviated or horizontal wellbores. Of course, in some examples, a tractor may be used in order to assist with deployment of the elongate medium in the wellbore. As the apparatus 10 is being deployed into the wellbore, the elongate medium is also deployed. Where the elongate medium is optical fibre, using well-known optical range finding methods, an instantaneous depth and/or speed of the apparatus may be calculated and displayed in real time at the surface.

[0184] Various materials and or techniques may be used to control deployment or unintentional unwinding of the elongate medium. For example, a wax, varnish, lacquer, grease or any other material with semi-sticky properties may be applied on the loaded elongate medium to keep the elongate medium from deploying unintentionally. In addition, for example, a friction device may be operably connected close to the launch point of the elongate medium to provide a friction force to prevent unintentional unwinding of the elongate medium.

[0185] In this example, as the elongate medium is deployed from outlet 318, isolating fluid 341 is also pulled out of the first chamber 322 into the wellbore from the outlet 318, for example via the boundary layer effect. As this occurs, the pressure inside the first chamber 322 is reduced due to an increase in free volume from both the deployment of the elongate medium 316 and the loss of isolating fluid 341. Isolating fluid 341 within the second chamber 324 will travel into the first chamber 322 via the flow path 326 to compensate for this pressure change in the first chamber 322. The outlet 318 is arranged such that there is no flow of bore fluid into the first chamber 322 via the outlet 318, for example a one-way valve may be provided.

[0186] The fluid inlet 328 provided in the housing allows fluid 342 from the wellbore to enter the second chamber as the apparatus 310 traverses a wellbore and the elongate medium 316 is deployed. Thus, the fluid inlet 328 acts as a pressure compensator. A one-way valve 329, for example a ball check valve may be provided at the inlet 328 to prevent isolating fluid 341 and bore fluid 342 from exiting via inlet 328. The in-flow of bore fluid 342 into the second chamber 324 as the elongate member is deployed assists in ensuring that isolating fluid 341 from the second chamber 324 flows into the first chamber 322 to compensate for volume changes in the first chamber 322.

[0187] In this example, the apparatus 310 is provided with a fluid inlet 328 and an outlet 318, wherein the outlet 318 is for both fluid and the elongate medium. The inlet 328 is positioned to allow the flow of bore fluid 342 into the second chamber 324. The outlet 318 is arranged to allow flow of isolating fluid 341 from the first chamber 322. As the apparatus 310 traverses the wellbore, bore fluid 342 enters the second chamber 324 via the fluid inlet 328. The isolating fluid 341 present in the second chamber 324 is driven from the second chamber 324 into the first chamber 322 via flow path 326. Isolating fluid 341 within the first chamber 322 exits the first chamber out into the wellbore via the outlet 318. The inlet 328 and outlet 318 are therefore arranged such that the flow path 326 through the apparatus 310 is from the second chamber 324 to the first chamber 322, and not vice versa.

[0188] In some examples, an additional outlet for fluid may be provided in addition to the outlet for the elongate medium. The additional fluid outlet where provided may comprise a one-way valve to prevent the flow of wellbore fluid directly into the first chamber 22 as the apparatus traverses the wellbore.

[0189] Accordingly, as the apparatus 310 traverses the wellbore and the elongate medium is deployed, the first chamber 322 remains filled with isolating fluid 341. As noted above, the filter 332 may be provided such that in the event bore fluid 342 does enter the first chamber 322, debris from the bore fluid 342 will be removed prior to the bore fluid 342 entering the first chamber 322. The elongate medium within the first chamber 322 is therefore protected from damaging exposure to bore fluid 342.

[0190] Where filter 332 is provided, the filter 332 may comprise a substantially cylindrical shape. The flow path through the filter 332 may also be cylindrical. Accordingly, the pressure drop across the filter 332 may be minimised, thus reducing the resistance to fluid flow from the second chamber 324 into the first chamber 322 as the apparatus 310 traverses the wellbore.

[0191] The volume of the second chamber 324 may be selected to be at least the same as or greater than the free volume of the first chamber 322 when the elongate medium is fully deployed to ensure that the second chamber 324 contains an adequate volume of isolating fluid 341 for the full deployment process.

[0192] The skilled person will appreciate that the alternative apparatus 310 of FIGS. 8a to 8c may also be used in a wellbore comprising a gas portion and a fluid portion, much like the wellbore 60 of FIGS. 2a to 2d. In this instance, prior to deployment, the first chamber 322 may be partially filled with isolating fluid 341 and partially with gas, and the second chamber 324 may be completely filled with isolating fluid 341. Alternatively, the first chamber 322 may be completely filled with gas and only the second chamber may be filled with isolating fluid 341. When used in such a wellbore, the apparatus 10 may function largely in the same way as the apparatus 10 of FIGS. 2a to 2d. For example, the ingress of bore fluid 342 into the cavity 311 via fluid inlet 328 may result in the isolating fluid 341 moving into the first chamber 322 and towards the outlet 318. This may provide for pressure to be balanced throughout the apparatus 310 as the elongate medium is deployed.

[0193] The elongate medium may be retrieved back to the surface after use. Alternatively, if a disposable elongate medium is used, the elongate medium may be released and allowed to remain in the wellbore. Such fibres that are configured to remain in the well may have applicability in relation to distributed sensing. In some embodiments, the elongate medium may degrade over time. However, such degradation may only occur after a time that the elongate medium has been used to perform sensing. It may be that is some cases, the deployed elongate medium (and any associated tools or other components) is only expected to be operable for a day or less, such as 12 hours, or less, or even 6 hours or less. In other words, the apparatus 10 may be constructed in such a manner that the survivability of the elongate medium, apparatus 10, etc. beyond a relatively short period is not expected. In such a way, the apparatus 10 can be constructed at reduced cost compared to a permanent installation.

[0194] The skilled person will realise that the above-described and illustrated examples are merely exemplary of the implementations of the present disclosure and that various improvements and modifications may be made thereto, without departing from the scope of the invention.

[0195] Furthermore, it should be understood that any features described in relation to one example, aspect or embodiment may also be used in relation to any other example, aspect or embodiment.