Method and apparatus for performing operations in fluid conduits

Abstract

A method and apparatus for cleaning a fluid conduit in a hydrocarbon production installation. The method comprises providing a composite pipe having a cleaning head coupled to a first end, and introducing the first end of the composite pipe and the cleaning head into a fluid conduit to be cleaned. Fluid is circulated between an annulus between an interior wall of the fluid conduit and the composite pipe, through a fluid circulation path defined by the cleaning head. The method comprises running the first end of the composite pipe and the cleaning head into the fluid conduit and cleaning at least one substance from the fluid conduit. An aspect of the invention relates to methods comprising circulating a heavy fluid through the fluid circulation path to reduce the effective weight of the pipe in the fluid conduit, and another aspect relates to a method comprising generating at least one pressure pulse in fluid in the fluid circulation path while imparting a pulling force or a pushing force on the pipe.

Claims

1. A method of cleaning a fluid conduit in a hydrocarbon production installation, the method comprising: providing an apparatus for cleaning a fluid conduit in a hydrocarbon production installation, the apparatus comprising: a composite pipe having a cleaning head coupled to a first end; a pressure control device, and an injector device for imparting a pushing and/or pulling force on the pipe; introducing the first end of the composite pipe and the cleaning head into the fluid conduit to be cleaned using the injector device for imparting the pushing and pulling force on the composite pipe; circulating fluid between an annulus between an interior wall of the fluid conduit and the composite pipe, and through a fluid circulation path defined by the cleaning head; running the first end of the composite pipe and the cleaning head into the fluid conduit; cleaning at least one substance from the fluid conduit; retrieving the composite pipe and the cleaning head using the injector device.

2. The method according to claim 1, wherein the composite pipe is a carbon fibre pipe or a carbon fibre polymer pipe.

3. The method according to claim 1, wherein the composite pipe comprises carbon fibre and a polymer in the polyaryletherketone (PAEK) family.

4. The method according to claim 1, wherein the composite pipe comprises an inner diameter in the range of 25 mm to 75 mm.

5. The method according to claim 1, wherein the composite pipe has a weight per unit length in water in the range of 0.25 kg/m to 2.5 kg/m.

6. The method according to claim 1, wherein the composite pipe has a tensile strength of greater than 2,000 kg.

7. The method according to claim 1, wherein the composite pipe has a collapse pressure rating in excess of 1,000 psi.

8. The method according to claim 1, wherein the composite pipe has a minimum elastic bending radius of less than 100 times the inner diameter of the pipe.

9. The method according to claim 1, wherein the composite pipe comprises a primary wall which is of unitary construction and provides axial tensile and radial compressive support to the composite pipe, and wherein the primary wall of the composite pipe is an outer wall of the composite pipe.

10. The method according to claim 1, comprising generating a thrust force on the cleaning head by circulating fluid through the circulation path.

11. The method according to claim 1, comprising circulating a heavy fluid through the fluid circulation path to reduce the effective weight of the pipe in the fluid conduit.

12. The method according to claim 11, wherein the heavy fluid is a brine.

13. The method according to claim 11, wherein the heavy fluid is a brine selected to reduce the effective weight of the pipe in the fluid conduit to below a weight threshold related to a maximum pulling and/or pushing force available to pull and/or push the pipe into the fluid conduit.

14. The method according to claim 11, wherein the heavy fluid has a density in the range of approximately 1.37 kg/l to 1.39 kg/l.

15. The method according to claim 11, wherein the heavy fluid has a density in the range of approximately 1.80 kg/I to 1.92 kg/I.

16. The method according to any claim 11, wherein the heavy fluid is selected to render the pipe neutrally or positively buoyant, or is selected to bring a negatively buoyant pipe towards a neutrally buoyant or positively buoyant condition.

17. The method according to claim 11, comprising exposing the pipe to the heavy fluid while imparting a pulling force or pushing force on the pipe.

18. The method according to claim 11, comprising circulating the heavy fluid in the fluid circulation path to fill the fluid conduit and/or pipe prior to imparting a pulling and/or a pushing force on the pipe.

19. The method according to claim 11, comprising circulating a cleaning fluid during a cleaning phase of the operation, and circulating the heavy fluid, which is different from the cleaning fluid, prior to, during, and/or subsequent to the cleaning phase.

20. The method according to claim 1, comprising generating at least one pressure pulse in fluid in the fluid circulation path while imparting a pulling force or a pushing force on the pipe.

21. The method according to claim 20, comprising generating a plurality of pressure pulses in a series of pressure pulses.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

(2) FIG. 1 is a schematic representation of an apparatus according to an embodiment of the invention;

(3) FIG. 2 is sectional view of a part of the apparatus of the embodiment of FIG. 1;

(4) FIG. 3 is a representation of a pipework section between a tie-in point and a riser, which is useful for understanding the benefits of the invention;

(5) FIG. 4 is a schematic representation of a pipeline system and apparatus according to the prior art; and

(6) FIG. 5 schematic representation of a pipeline system and apparatus according to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(7) The invention has application to the cleaning operations for subsea pipelines, including blockage and/or debris removal, and is particularly advantageous in cleaning operations in which the pipeline is accessed from surface via a marine, catenary and/or flexible riser. Accordingly, the invention will be described in the context of such an operation by way of example only.

(8) Referring firstly to FIG. 1, there is shown an apparatus according to an embodiment of the invention, generally depicted at 100. The apparatus 100 (shown in more detail in FIG. 2) is formed from a cleaning head 102 and a pipe 104, which in this case is composite pipe formed from a carbon polymer material. The apparatus 100 is shown here in situ in a fluid conduit 112, which in this case is a flexible riser. The apparatus 100 is deployed from a storage reel 114 via an injector unit 116 and a pressure control device 118 comprising a stripper and blow out preventer (BOP) unit.

(9) The injector unit 116 comprises a drive mechanism for pushing and/or pulling the pipe into and out of the fluid conduit through the pressure control apparatus 118. The drive mechanism comprises an arrangement of blocks shaped and sized to engage with the outer surface of the composite pipe.

(10) The stripper comprises internal pack off elements formed from an elastomeric material, arranged to provide a fluid seal with the outer surface of a composite pipe passing through the unit. The stripper allows the composite pipe to pass through the apparatus while retaining pressure in the conduit system beneath the stripper.

(11) The blowout preventer comprises a shear and seal blowout preventer, which has the capability to cut or otherwise sever composite pipe introduced to the fluid conduit. This embodiment also comprises a chamber which functions as a lubricator, providing an access point for the coupling of the cleaning head 102 to the composite pipe. A divertor (not shown) is also provided to create a fluid inlet for fluid pumped into the annulus between the introduced composite pipe and the inner surface of the fluid conduit 112.

(12) A control module 120 communicates with the other elements if the system to control its operation and receive data collected from the apparatus 100. The control module comprises a pump and an arrangement of valves, including a controllable valve which enables the bore of the pipe to be exposed to a pressure differential to generate one or more pressure pulses in the pipe bore.

(13) FIG. 2 shows the apparatus 100 in more detail. The cleaning head 102 comprises a body 106 coupled to the composite pipe 104 by a connector 132. The body defines a throughbore 108 from a leading end 110 of the cleaning head to a trailing end 111 joined to the composite pipe 104. The throughbore 108 is continuous with the flow bore 126 of the composite pipe 104 and therefore there is a flow path through the cleaning head to the composite pipe and to surface.

(14) The cleaning head 102 comprises a flow direction arrangement 130, supported by the body 106, which provides a fluid circulation path between the annulus 124 located between an interior wall of the fluid conduit and the body and the throughbore. In this embodiment, the flow direction arrangement defines a convoluted fluid path for fluid passing down through the annulus to the cleaning head, and out through an outlet 122 at the leading end 110. As the fluid passes through the flow direction arrangement 130, a thrust force is generated on the cleaning head to deploy it into the fluid conduit 112. The magnitude of the thrust force is controlled by the pressure of fluid pumped down in the annulus from surface. The design of the flow direction arrangement 130 is in this embodiment in accordance with the principles described in WO2014/102549 (the contents of which are incorporated into this specification by reference), with suitable modifications to connect the cleaning head to a composite pipe 104. In addition, in embodiments of the present invention the cleaning head need not create a seal with the interior of the conduit in order to generate sufficient thrust to deploy the apparatus (which is lighter than the coiled tubing systems in which such thrusters are often used).

(15) The composite pipe of this embodiment is a carbon fibre polymer pipe, formed from continuous carbon fibres and polyether ether ketone (PEEK), with an inner diameter of 47 mm. The pipe comprises an outer wall which is of unitary construction and forms the primary structure which supports the pipe against longitudinal tensile and radial compressive forces. The composite pipe is spoolable, and has a minimum bend radius of approximately 20 to 50 times the inner diameter of the pipe. The composite pipe has a weight per unit length in water of 0.65 kg/m and a tensile strength of around 41,000 kg. The composite pipe has a collapse pressure rating of around 5,000 psi, and a working pressure of around 5,000 psi.

(16) In use in a blockage removal application, the apparatus is conveyed to the desired location from surface by circulation of a deployment fluid (not shown) which generates a thrust on the cleaning head. When the cleaning head is in the desired location and at the desired distance from the blockage a treatment fluid is pumped from surface down the annulus cleaning head, where it passes through the cleaning head to the surface of the blockage.

(17) The use of composite pipe in this embodiment invention offers advantages over steel coiled tubing wellbore cleaning systems and flexible hose cleaning systems of the prior art, as will be described below in the following exemplary applications of the apparatus and systems.

(18) FIG. 3 is a representation of pipework at the surface of hydrocarbon production system disposed between a tie-in point and an opening to a riser which leads to a subsea pipeline (not shown). The pipework, general shown at 200, comprises a number (in this case six) of bends 204 between the upper end 201 and the lower end 202 of the pipework. A flowline, which in this case is the apparatus 100, is shown in situ in the pipework, and illustrates the path that the apparatus 100 needs to follow from its tie in point on its way to the cleaning location subsea. Similar, FIG. 3 shows the path through which the apparatus 100 must be withdrawn when the apparatus is pulled from the conduit at the end of the operation.

(19) FIG. 3 illustrates a problem of the effect of friction on the pulling and/or pushing force required to move the apparatus 100 along the pipework, when the pipe is in tension. The force obeys the Capstan Equation:
T.sub.load=T.sub.loade.sup.μφ,

(20) where T.sub.load is the applied tension on the line, T.sub.hold is the resulting force exerted at the other end of the line, μ is the coefficient of friction between the pipe and inner wall of the fluid conduit, and φ is the total angle swept by all turns of the pipe, measured in radians (i.e., with one full turn the angle φ=2π).

(21) Thus the tension at one of the pipe gains exponentially with respect to the angle swept by the pipe, and it is apparent that minimising the friction on the pipe is beneficial to enable the pipe to be moved in the pipework during deployment or retrieval.

(22) During deployment of the apparatus, tension in the pipe can be reduced or eliminated by providing a pushing force at the injector unit, while circulating fluid to generate thrust at the cleaning head in a conventional manner. However, when retrieving the apparatus, there is an inherent friction between the pipe and the fluid conduit which creates tension in the pipe, and cannot be overcome by reversing the direction of fluid circulation. This is illustrated with the benefit of FIG. 4, which schematically shows a pipeline system 400, with a conventional apparatus 410 having been deployed from surface down a riser 402 to a subsea pipeline 404. A horizontal section of coned tubing 412 rests on the bottom of the subsea pipeline 404, and the friction between the tubing 412 and the pipeline 404 must be overcome to retrieve the apparatus (in addition to the hanging weight of the vertical pipeline section in the riser). The pulling force required to overcome the horizontal friction and hanging weight is subject to capstan friction gains as the pipe is drawn through additional bends in the pipework between the tie-in point and the riser.

(23) An additional capstan friction effect is created at the inner radius of the bend 406, as the tubing 412 transitions between the horizontal and vertical sections, due to the tension in the pipe causing movement of the pipe in the conduit to the wall on the inside of the bend. As well as increasing the overall friction required to be overcome by the pulling force and exacerbating the capstan effect, when conventional coned tubing is used 412, there is a significant risk of damage to the wall of the fluid conduit on the inside of the bend. This damage could result in catastrophic failure of the riser.

(24) The present invention enables this effect to be mitigated. Firstly, the use of composite pipes, such as the pipe of the present embodiment, reduces the friction between the pipe and the fluid conduit as the materials have a lower coefficient of friction than the steel coned tubing and the inner wall of the fluid conduit.

(25) Secondly, the mass per unit length of composite pipe is significantly less than the mass per unit length of the steel coiled tubing conventionally used. This naturally reduces the pulling force required, and lowers the initial tension which is subject to capstan gains.

(26) Furthermore, the lower mass per unit length enables the use of heavy fluids, such as brines, to further reduce the friction in accordance with embodiments of the invention.

(27) FIG. 5 illustrates schematically a pipeline system 500, with an apparatus 100 having been deployed from surface down a riser 502 to a subsea pipeline 504. In a method according to an embodiment of the invention, a heavy brine is circulated through the apparatus to fill the fluid conduit and the pipe 104. The brine is selected to reduce the effective weight of the pipe in the fluid conduit to below a weight threshold. In this case, the brine is a mixture of calcium chloride (CaCl.sub.2) and calcium bromide (CaBr.sub.2) brines selected to have a density of 1.55 kg/l (about 12.9 ppg), which is sufficient to render the pipe 104 neutrally buoyant, and lift the horizontal section of the pipe 104 from the subsea pipeline. This substantially eliminates friction effects between the pipe 104 and the subsea pipeline, and significantly reduces the friction between the pipe 104 and the inner surface of the fluid conduit between at the bend 506. The hanging weight of the vertical part of the pipe 104 is also substantially eliminated, and therefore the tension in the pipe beneath the pipework 200 is very small. This significantly reduces the effect of capstan friction in the convoluted pipework during retrieval of the apparatus.

(28) It will be appreciated that other brines, of other densities, could be used to render the pipe positively buoyant, or to bring a negatively buoyant pipe towards a neutrally buoyant or positively buoyant condition (without necessarily reaching neutral or positive buoyancy).

(29) The brine may for example be selected from a brine selected from the group comprising potassium chloride (KCl), sodium chloride (NaCl), potassium bromide (KBr), calcium chloride (CaCl.sub.2), sodium bromide (NaBr), calcium bromide (CaBr.sub.2), zinc bromide (ZnBr.sub.2). Other brines, for example those marked by Halliburton Energy Services Inc. under the BRINEDRIL-N® brand may be used in alternative embodiments of the invention.

(30) A brine of calcium chloride may be preferred as it is readily available and is known to have properties acceptable for use in hydrocarbon applications, although it is not suitable for completely floating the pipe in the foregoing example (resulting in a weight per unit length of 0.2 kg/l).

(31) It will be appreciated that the heavy fluid may be circulated in the fluid conduit in a dedicated deployment or retrieval phase of the operation, and in different phases, alternative (lighter) fluids may be circulated, including dedicated cleaning or treatment fluids.

(32) In an alternative embodiment of the invention, the composite pipe of this embodiment is a glass fibre reinforced polymer pipe, for example of the type described in GB2337569, with an inner diameter of 50.8 mm. The pipe comprises an outer wall which is of unitary construction and forms the primary structure which supports the pipe against longitudinal tensile and radial compressive forces. The composite pipe is spoolable, and has a minimum bend radius of approximately 20 to 50 times the inner diameter of the pipe. The composite pipe has a weight per unit length in water of 2.0 kg/m and a tensile strength of around 9,500 kg. The composite pipe has a collapse pressure rating of around 2,200 psi, and a working pressure of around 3,500 psi. In this example, the brine density required to render the pipe neutrally buoyant is 3.47 kg/l or 29 ppg, which is very high and beyond the reach of most readily available brines. Therefore in this embodiment, a brine of lower density, such as calcium bromide, is used to reduce the weight of the pipe in the fluid conduit and reduce the force required to pull the pipe from the fluid conduit (thereby having a positive effect on capstan friction).

(33) In addition, in order to further reduce the effect of friction, a method of this embodiment of the invention comprises generating a pressure pulse in the pipe to create a fluid-surface interaction which temporarily reduces the coefficient of friction between the pipe and the fluid conduit at all contact points along its length.

(34) The apparatus 100 includes control module 120 with a pump and a controllable valve, which enables the pipe and/or the annulus to be exposed to a pressure differential, when the valve is opened. In this embodiment, the valve is controllably opened to generate a series of positive pressure pulses, having a magnitude greater than 200 psi (over a base pressure of around 2,000 psi), a duration of 0.5 seconds and a frequency of 1 Hz. The propagation of the positive pressure pulse in the pipe causes a fluid-surface interaction which temporarily reduces the frictional effect between the pipe and its contact points in the fluid conduit. While the pulses are being transmitted, a pulling force is applied to the pipe by the injection unit in order to retrieve the apparatus.

(35) The invention provides a method and apparatus for cleaning a fluid conduit in a hydrocarbon production installation. The method comprises providing a composite pipe having a cleaning head coupled to a first end, and introducing the first end of the composite pipe and the cleaning head into a fluid conduit to be cleaned. Fluid is circulated between an annulus between an interior wall of the fluid conduit and the composite pipe, through a fluid circulation path defined by the cleaning head. The method comprises running the first end of the composite pipe and the cleaning head into the fluid conduit and cleaning at least one substance from the fluid conduit. An aspect of the invention relates to methods comprising circulating a heavy fluid through the fluid circulation path to reduce the effective weight of the pipe in the fluid conduit, and another aspect relates to a method comprising generating at least one pressure pulse in fluid in the fluid circulation path while imparting a pulling force or a pushing force on the pipe.

(36) The invention facilitates application to a wide range of fluid conduit systems. The use of composite pipe in the first aspect of the invention offers advantages over steel coiled tubing wellbore cleaning systems and flexible hose cleaning systems of the prior art. The use of composite pipe facilitates application to a wide range of fluid conduit systems. The use of composite pipe reduces the force required to pull out and/or inject a cleaning apparatus from and/or into a fluid conduit; increases the depth to which a cleaning apparatus can be deployed into a fluid conduit; and reduces the damage to a fluid conduit during a deployment and/or pulling of a cleaning apparatus into and/or from a fluid conduit.

(37) Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those expressly claimed herein.