NO344601B1

NO344601B1 - Assembly for an oil and gas production platform or rig, and related methods

Info

Publication number: NO344601B1
Application number: NO20161719A
Authority: NO
Inventors: Alistair Iain Macleod
Original assignee: Bri Cleanup As
Priority date: 2016-10-31
Filing date: 2016-10-31
Publication date: 2020-02-10
Also published as: US20200056469A1; WO2018080323A3; WO2018080323A2; AU2017349493A1; EP3532697A2; NO20161719A1

Description

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ASSEMBLY FOR AN OIL AND GAS PRODUCTION PLATFORM OR RIG, AND RELATED METH-

ODS

Technical field

5 The present invention relates to the processing of production fluid from wells and, in particular, to the removal of solids to clean such fluid. Furthermore, it relates in various examples to an assembly for an oil and gas production platform or rig, a method of equipping a Christmas tree for processing fluid from at least one oil and gas production, and a method of performing an intervention operation through a vertical bore of the Christmas tree.

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Background

In the oil and gas exploration and production industry, fluid travels out of and is extracted from a wellbore in various situations. During hydrocarbon production for example, production fluid containing hydrocarbons from a subterranean reservoir is conventionally produced by a well, driven to

15 the surface along the well by the pressure from the subsurface. The fluid exits the well from a wellhead, passes through a valve tree (typically termed the ‘Christmas’ tree), and is directed through transport pipes to a processing system for processing the fluid to bring the hydrocarbons into condition for export to end users. In offshore environments, depending on the type of well, the wellhead may be positioned subsea at the seabed, or on the well floor of a production platform.

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Typically, the wellhead has the valve tree mounted upon it, providing an access point to the well and containing valves for closing and sealing the well with double-pressure barriers. Normally, the valve tree has the ability to allow connection of service or intervention equipment via the “service wing” inlet of the valve tree while production can continue with a flow of produced fluid from the res-

25 ervoir via the “production wing” outlet of the valve tree. When servicing is required, access via the service wing is provided through the opening of the appropriate valves.

The produced fluid from the well passes from the valve tree through a production choke, typically a series of production chokes, which is used to control the flow of fluid from the well and is arranged

30 to be closed to stop the flow of production fluid from the well if required. It may also be used to reduce or increase the rate of flow of production fluid.

A particular challenge during production is that the composition of the production fluid is generally a mixture of liquid and gas, often with some solids such as sand particles entrained in the fluid. The

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processing system downstream from the valve tree is provided to process the fluid and may include various stages of separation etc., to remove unwanted solids, and separate gas from liquid hydrocarbon components. A difficulty is that the composition of the fluid from the well can change over time and may not be predictable. Therefore, the processing system may typically be poorly suited

5 for handling such changes or certain types of flow. Moreover, multiple wells may be connected to one processing system, and the composition of fluid between different wells may be widely different, as can quantities of solids. Collectively, such changes can result in the processing system being incapable of managing the production process as originally intended. Accordingly, there is a need for alternative methods to be explored to accommodate the production changes.

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In addition, as a reservoir depletes over time, the amount of solids in the production fluid can tend to increase. The presence of solids such as sand in the production fluid can give rise to problems in handling by the processing system and can cause abrasion and damage to pipework and related components. To address this, a typical approach is to reduce the rate of flow from the well, which

15 reduces the tendency to draw solids out of the well with the production allowing the processing system to process the fluid. But, lower rates of hydrocarbon production are achieved as a result.

On some platforms, additional separation equipment is installed when required, e.g. solids separation units such as a de-sander used on a temporary basis, in order to remove solids from the pro-

20 duction flow before it enters the processing system. Use of equipment such as de-sanders or similar devices can allow for higher production rates.

Deck space on offshore platforms is often limited and at a premium. In many cases, any need for de-sanders or similar devices to promote production may not have been foreseen in early platform

25 designs. As such, de-sanders on early platforms have simply been placed in deck areas wherever available, with temporary pipework being installed and configured to divert production fluid out of the permanent production system into the de-sander and then back into the permanent production system once the solids are removed by the de-sander.

30 However, the provision of de-sanders in this manner may not be convenient or efficient. Typically, the flow of fluid passes through significant lengths of pipework and through valves such as the production choke, and with solids present exposes such components to abrasion and damage. Therefore, even with a de-sander installed as described above, production rates may need to be lowered to preserve related components and equipment.

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An example de-sander is described in patent publication number WO03099448 (Arefjord).

The patent publication US2005/061515 describes apparatus for flowing a subsea well.

40 Summary of the invention

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According to a first aspect of the invention there is provided an assembly for an oil and gas production platform or rig, the platform or rig having a Christmas tree deck and a hatch deck above the Christmas tree deck, the assembly comprising: a Christmas tree connected to a top of a wellhead on the platform or rig, the Christmas tree located at the Christmas tree deck; and a processing unit

5 comprising at least one separator, positioned above and connected onto a top of the Christmas tree, the Christmas tree bearing at least partially the weight of said separator; wherein the separator is configured to be operable for receiving production fluid from at least one oil and gas production well and removing solids to clean the production fluid.

10 The assembly may have further features as set out in any of the dependent claims 2 to 15 as appended hereto.

According to a second aspect of the invention there is provided a method of equipping a Christmas tree for processing fluid from at least one oil and gas production well using the assembly according

15 to the first aspect of the invention, the method comprising: providing a processing unit comprising at least one separator onto the Christmas tree such that the separator is at least partially supported on top of the Christmas tree; and positioning the processing unit with respect to the valve tree, to position the processing unit in an operating position in which the separator is operable to receive production fluid from at least one oil and gas production well and clean the production fluid.

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The method may be performed to equip the Christmas tree on an oil and gas production platform or rig, said platform or rig having a Christmas tree deck and a hatch deck above the Christmas tree deck, wherein the Christmas tree may be arranged at the Christmas tree deck, and the method may include the step of lowering the processing unit through a hatch in the hatch deck onto the

25 Christmas tree, so as to locate the separator in place in the operating position, at least partially supported on the top of the Christmas tree.

According to a third aspect of the invention there is provided a method of performing an intervention operation through the vertical bore of the Christmas tree in variants of the assembly according

30 to the first aspect of the invention in which: the Christmas tree has a vertical bore for accessing the well by an intervention or another tool lowered on a wireline or tubing from above the vertical bore through said tree; and the processing unit is further arranged to provide full diameter access to the vertical bore of the Christmas tree; the operation performed by lowering intervention equipment through the vertical bore, while the separator remains in place and is at least partially supported on

35 the top of the Christmas tree.

The separator may comprise a device as described in the claims of WO03099448 (Arefjord), or may be operated to perform a method as described in the claims of WO03099448 (Arefjord).

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Embodiments of the invention can be advantageous as will be apparent from throughout the description, claims, and drawings.

Any of the various aspects of the invention may include the further features as described in relation

5 to any other aspect, wherever described herein. For instance, any of the aspects may further comprise any feature defined in any one or more of the dependent claims appended hereto. Features described in one embodiment may be combined in other embodiments. For example, a selected feature from a first embodiment that is compatible with the arrangement in a second embodiment may be employed, e.g. as an additional, alternative or optional feature, e.g. inserted or exchanged

10 for a similar or like feature, in the second embodiment to perform (in the second embodiment) in the same or corresponding manner as it does in the first embodiment.

Description and drawings

There will now be described, by way of example only, embodiments of the invention with reference

15 to the accompanying drawings, in which:

Figure 1 is a schematic representation of an assembly comprising apparatus for processing fluid from a well according to an embodiment of the invention;

Figure 2 is a part-sectional representation of the apparatus of Figure 1 in close-up, the ap-

20 paratus including a valve tree provided with a separator and a flow tube;

Figure 3 is a part-sectional representation of the apparatus of Figure 2 along the line I-I; Figure 4 is a part-sectional representation showing details of the separator for the apparatus of Figure 2 where the separator includes a degasser according to one embodiment of the invention;

25 Figure 5 is a part-sectional representation showing details of the separator for the apparatus of Figure 2 where the separator includes a sand cleaner according to another embodiment;

Figure 6 is a part-sectional representation showing details of the separator for the apparatus of Figure 2 where the separator has parallel de-sanders, according to yet another

30 embodiment;

Figure 7 is a schematic representation of an assembly comprising apparatus for processing fluid from a well according to an embodiment of the invention;

Figure 8 is a top view representation of part of the apparatus of Figure 7;

Figure 9 is a schematic representation of apparatus for processing fluid from a well accord-

35 ing to another embodiment of the invention;

Figure 10 is a schematic representation of apparatus for processing fluid from a well in an intervention mode according to an embodiment of the invention;

Figure 11 is a schematic representation of apparatus for processing fluid from a well in an intervention mode according to another embodiment of the invention;

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Figure 12A is a schematic part-sectional representation of a valve tree provided with a separator and a removable flow tube, wherein the flow tube is in a stand-by position, according to an embodiment of the invention;

Figure 12B is a schematic part-sectional representation of a valve tree provided with a separa-

5 tor and a removable flow tube, wherein the flow tube of Figure 12A is in a deployed position;

Figure 13A is a schematic part-sectional representation of a valve tree provided with a separator and a retractable flow tube, wherein the flow tube is in an inactive position, according to an embodiment of the invention;

10 Figure 13B is a schematic part-sectional representation of a valve tree provided with a separator and a retractable flow tube, wherein the flow tube of Figure 12A is in an active position; and

Figure 14 is a schematic part-sectional representation of apparatus for processing fluid from a well where a separator includes parallel de-sanders according to an embodiment

15 of the invention.

With reference first to Figure 1, part of an offshore platform 1 is illustrated with apparatus 10 provided for processing fluid from a well. The apparatus 10 includes a valve tree 12 arranged at a valve tree deck 2 of the platform. The valve tree 12 is connected to the top of a wellhead 5 of the

20 well.

The platform 1 also has a hatch deck 3 above the valve tree deck 2 as indicated in Figure 1. The hatch deck 3 has hatches 4a-4c which facilitate access to valve trees positioned below, at the valve tree deck 2.

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During production from the well, production fluid travels downstream through the apparatus 10 to a well choke 30, and onward to a downstream processing system 50.

The apparatus 10 includes a processing unit 16 in the form of a dynamic de-sander (a separator)

30 which is mounted onto the valve tree 12. The de-sander receives the production fluid from the well through a main bore 13 of the valve tree 12, as indicated by arrows A, removes unwanted solids such as sand or the like from the raw production fluid from the well, and produces an output of clean production fluid from the processing unit 16 which no longer contains the removed solids.

35 The apparatus 10 includes a flow tube 17 which in Figure 1 is inserted inside the valve tree 12 bridging a service wing bore 14 and a production wing bore 15 of the valve tree 12 (the flow tube 17 constituting a “bridge tube”). The clean production fluid is fed from the de-sander, back through the valve tree 12 through the flow tube 17, as indicated by arrows B, and onward to the well choke 30 and to the downstream processing system 50, which may be a downstream processing system

40 as described hereinabove.

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In this way, the well choke 30, the downstream processing system 50, and the pipework between the valve tree 12 and the processing system 50 can avoid undesired exposure to the solids content in the raw fluid from the well.

5

With further reference to Figures 2 and 3, the apparatus 10 can be seen in further detail. The valve tree 12 is in the form of a typical Christmas tree on a wellhead. The main bore 13 is vertical and has an upper bore portion for accessing a top end of the main bore 13. The tree 12 additionally has side bores including the production wing bore 15 and the service wing bore 14 for alternative

10 entry or exit routes through the tree to the well.

The valve tree 12 includes two main bore valves 18, 19 which can selectively be closed to shut off the well providing a double barrier against well pressure, or opened to allow fluid flow through the valve tree 12. As can be seen, the main bore valves 18, 19 are positioned at a location along the

15 main bore below the level of the service wing and production wing bores 14, 15.

The service wing bore 14 has a service wing valve 24 for closing/opening the service wing bore 14, and similarly the production wing bore 15 has a production wing valve 25 for closing /opening the production wing bore 15. When closed, these valves 24, 25 seal the service wing and production

20 wing bores 14, 15 to prevent fluid flow therethrough. Conversely, when they are open, access to the valve tree 12 and fluid flow is permitted. The upper bore portion of the main bore 13 also has an upper main bore, provided with swab valve 23 for closing/opening the upper main bore portion 13 for preventing/permitting fluid communication and/or access therethrough.

25 As will be appreciated, the valves 18, 19, 23, 24 and 24 are merely illustrated schematically in the figures. Each of these valves may be in the form of a ball valve or the like, having a barrel which is activated by operation of the valve and which obturates the bore to close it, and seals against a wall section of the bore to seal against well pressure.

30 In another example as illustrated in Figure 4, the apparatus 10 has a processing unit 116 in place of the processing unit 16 described above. The processing unit 116 is illustrated in the form of a hub in which a de-sander 127 is mounted together with other components for processing fluid, providing a compact unit with the necessary components for processing and cleaning the fluid from the well.

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In particular, the processing unit 116 in this variant includes a degasser 126 for removing gas from the production fluid, a de-sander 127 for removing solids, and a solids container 128 for storing the separated solids from the de-sander 127 for disposal. The processing unit 116 includes a pipe section 122 (constituting a body with a throughbore) provided with a connector 121 for rigidly con-

40 necting the processing unit to the top of the valve tree 12. The interior of the pipe section 122 is

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arranged to be in fluid communication with the main bore 13 of the valve tree 12. The de-gasser 126, the de-sander 127, and the solids container 128 each comprise a processing tank which is mounted to the pipe section 122 via connecting brackets 129a, 129b. The connector and pipe section 121 provide for mounting of the de-sander 127 and the other components and for attaching

5 these onto the top of the valve tree 12, providing both fluid connection and structural support for the de-sander 127. The connection to the valve tree 12 is such that the valve tree 12 bears the weight of the processing unit 116. In other examples, the de-sander 127 and the other equipment may be mounted on a rigid frame, e.g. of steel or other high-strength material, which is connected onto the valve tree 12.

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During production of fluid from the well in the present example, the production fluid travels upward through the main bore 13 of the tree 12 and along the pipe section 122. The fluid enters the degasser 126 through a port in the wall of the pipe section 122 and through a degasser inlet 126i. Gas from the fluid is bled off through a gas outlet 126g, and the degassed fluid exits the de-gasser

15 through outlet 126x and into the de-sander 127i via a de-sander inlet 127i. The dashed line R indicates the route of the fluid from the degasser to the de-sander 127.

In the de-sander 127, solids are separated out of the fluid to produce a clean production fluid no longer containing the removed solids. The cleaned production fluid then exits the de-sander 127

20 through the outlet 127x, and passes through a flow line and back through the valve tree 12 via the flow tube 17, and onward to the choke 30 and the processing system 50 downstream. The gas from the outlet 126g is reintroduced and combined with the cleaned production fluid, e.g. via a connection (not shown) to the outlet 127x.

25 The solids which are separated out by the de-sander 127 may selectively be disposed from the desander 127 through a first solids outlet 127s or passed on to the solids container 128 through a second solids outlet 127t and into the tank of the solids container through inlet 128i. Solids from the solids container 128 may later be disposed via an outlet 128x.

30 Valves on the inlet and/or outlet lines are indicated with solid fill to indicate a closed valve and no fill to indicate an open valve. The valves may all be controllable so as to be opened or closed to control and guide the flow of fluid, and optionally shut off fluid flow, according to requirements. In Figure 4, the valves are closed on the first and second outlets 127s, 127t. Thus, separated solids are not being transferred from the de-sander to the solids container 128, in the instance shown.

35 The flow valves on the inlets 126i, 127i and the outlet 127x are open, allowing for the production fluid to progress through the degasser and then the de-sander before the cleaned production fluid travels through the valve tree 12 downstream.

The de-sander 127 may be one as described in WO03099448 (Arefjord).

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Turning now to Figure 5, another example is illustrated with a different processing unit 216 in the apparatus 10 in place of those described above. Features corresponding to ones described in relation to the processing unit 116 are denoted with the same reference numerals but incremented by one hundred, and may not be explicitly described again here.

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In this case, the processing unit 216 does not have the degasser, but instead has a solids cleaner 220 mounted on a pipe section 222 via connecting brackets 229a, 229b, together with a de-sander 227 and a solids container 228.

10 Production fluid from the well travels upward from the main bore 13 of the valve tree 12, along the pipe section 222 and through a port in the wall of the pipe section 222 into the de-sander 227 via the de-sander inlet 227i. The path taken by the fluid entering the de-sander 227 is indicated by the broken line R in Figure 5. Cleaned production fluid from the de-sander 227 is then circulated back to the valve tree 12 from the outlet 227x in the same manner as described above.

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Separated solids contained in the solids container 228x may be transferred via the solids outlet 228x to the solids cleaner 220, entering the solids cleaner 220 through the cleaner inlet 220i. In the solids cleaner 220, the solids may be contained in a tank in which the solids undergo treatment to remove contaminants from the solids. The decontaminated or cleaned solids may then be dis-

20 posed from the solids cleaner 220 via an outlet 220x.

In Figure 6, another example is illustrated with a different processing unit 316 in the apparatus 10 in place of those described above. Features corresponding to ones described in relation to the processing units 116 or 216 are denoted with the same reference numerals but incremented by two

25 hundred or one hundred respectively, and may not be explicitly described again here.

In this variant, the processing unit 316 has two parallel de-sanders 327a, 327b provided with corresponding solids containers 328a, 328b, all which are mounted hub-wise together on a pipe section 322 connected via the connector 321 to the valve tree 12. The de-sanders 327a, 327b are pro-

30 vided on either side of the pipe section 322. The pipe section 322 is in fluid communication with main bore 13 of the valve tree 12.

In the example of Figure 6, during production, production fluid passes upward from the valve tree 12 along the pipe section 322 and enters into the de-sanders 327a and 327b through respective

35 flow ports through the wall of the pipe section 322 and respective de-sander inlets 327i.

Full diameter access to the main bore 13 of the valve tree 12 is provided by the pipe section 322, which can be beneficial for performing well intervention or other operations in the well whilst the processing unit is installed. This functionality will be described in further detail below.

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Referring now to Figure 7, apparatus 110 for processing fluid from a well is installed on the offshore platform 1. The apparatus 110 includes the valve tree arranged as in the embodiments above with a flow tube 17 arranged inside the tree. In this example, however, a processing unit 400 is provided in contrast to those of the apparatus 10 described above.

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The processing unit 400 is a compact unit with components mounted in a hub, designed to be deployed and installed in the location A, by lowering the processing unit 400 through the opening of the hatch 4b onto the valve tree 12. The width of the processing unit 400 is therefore less than the lateral extent of the hatch 4b to allow it to fit through the opening. The processing unit 400 occu-

10 pies only the space below the hatch, within the lateral dimension of the opening of the hatch 4b in the hatch deck 3. The part of the pipe section 422 between the processing unit 400 and the top of the valve tree 12 in this example is made sufficiently short to fit the de-sander within the space between the valve tree deck 2 and the hatch deck 3.

15 In the installation location A as shown, the processing unit 400 is attached to the valve tree 12 via a connector hub 421 and a pipe section 422 which provides for fluid communication and/or access to the main bore 13 of the valve tree from a top end of the processing unit 400, if required. The processing unit 400 is disposed in a column of space C extending upward from the valve tree through the opening of the hatch, the column width being defined by the width of the hatch opening.

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The processing unit 400 includes first and second de-sanders 427a, 427b, a choke manifold 461, and an emergency shutdown (ESD) valve 462. Production fluid passes via the pipe section 422 into the de-sanders 427a, 427b, through a choke of the choke manifold 461 and through the ESD valve 462. In some variants, the choke manifold 461 may provide a well choke which may be con-

25 trollable to control fluid flow and/or shut off flow from the well. In this variant, the choke in the choke manifold 461 may replace the well choke 30, so that clean fluid from the de-sander 427a, 427b may travel directly to the downstream processing system 50 without going via the normal well choke 30, or without needing to use the well choke 30.

30 Fluid circulates otherwise as described in the embodiments above. That is, the production fluid travels upward through the main bore 13 of the valve tree 12, and passes through the de-sanders 127a, 127b. Clean production fluid from the de-sanders 127a, 127b travels back out of the processing unit 400 through the valve tree via the flow tube 17 and onward downstream from the valve tree 12, e.g. to the downstream processing system 50.

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Figure 8 illustrates the arrangement of the processing unit 400 from above with the hatch 4b open and when installed in the installation location A and/or when being lowered through the opening of the hatch 4b. As can be seen, the processing unit 400 fits through and is arranged laterally within the opening of the hatch 4b. The tanks of the de-sanders 427a, 427b are eccentrically positioned

40 to either side of the pipe section 422. The pipe section 422 is provided centrally, and provides an

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access conduit for communication with the main bore 13 of the valve tree 12 when the processing unit 400 is mounted upon the tree 12. The tanks of the de-sanders 427a, 427b are rigidly connected to the pipe section 422 via connecting members 429a, 429b, and to the connector hub 421 (not shown in Figure 8), permitting the lowering of the de-sander as a unit from above the hatch

5 deck, through the hatch 4b and into position A on the valve tree. The processing unit 400 may be fitted with a pipe flange, e.g. on the connector hub 421, for sealed mating with and connection to a corresponding flange of tree above the swab valve 23.

In Figure 9, a variant is exemplified where the processing unit 400 is installed above the hatch deck

10 3, in an installation location B. In this case, the pipe section 422 includes a riser 422r which passes upward through the opening of the hatch 4b between the processing unit 400 and the valve tree 12. The processing unit 400 is confined to the column of space C through the opening of the hatch, which can advantageously provide for the processing unit 400 to be used on the rig without intruding into other areas of the hatch deck. The processing unit 400 may also remain installed while full

15 diameter access to the well may be provided via the pipe section 422 and the riser 422r. Production fluid from the well thus passes up from the well through the valve tree 12 through the riser 422r and into the de-sanders 427a, 427b before returning from the processing unit 400 back through the valve tree 12 and the flow tube 17 as in the embodiment of Figure 8.

20 Turning to Figure 10, the apparatus 110 is illustrated in another mode of operation for performing a well intervention in the well. The processing unit 400 is installed in the location A, on the top of the valve tree 12, and is used to clean fluid returning from the well. An intervention tool 40 is being lowered into the well through the pipe section 422. The flow tube 17 as utilised in the above described embodiments is removed and not used in this mode. There is therefore no flow tube 17 in

25 the main bore 13 of the valve tree, and the intervention tool 40 has full diameter bore access to the well through the pipe section 422 and the valve tree 12. In this case, the pipe section 422 includes an intervention riser 422i which extends through the hatch 4b up from the top of the processing unit 400 and connects with an intervention interface above the hatch 4b. The intervention interface may include intervention control equipment, such as valves for pressure containment, etc., during

30 an intervention operation.

The intervention tool 40 is deployed on a wireline 41 in this example. However, it will be appreciated that the intervention tool 40 may be of many different kinds, depending upon the nature of the intervention operation to be performed in the well. Accordingly, the intervention tool in other em-

35 bodiments may be deployed on jointed pipe, or coiled tubing, instead of the wireline 41.

Likewise, in certain embodiments, operation of the intervention tool may require circulation of a fluid into the well, e.g. through the centre of a jointed pipe string, and back out of the well through an annulus up to the surface. In such an embodiment, the processing unit 400 can be used to pro-

40 cess the returning fluid from the annulus, e.g. to remove solids from the fluid. Clean fluid, without

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the removed solids, may then be passed via the well choke, which may be operated for pressure control or the like of the well during the intervention.

The arrangement of the processing unit 400 illustrated in Figure 10 may therefore be utilised with

5 production wells during production of oil and gas from the well, but also during well construction, or when production of oil and gas is not taking place.

In Figure 10, the route of the fluid from the wellhead 5 upward into the pipe section 422 and out of the processing unit 400 is indicated by a broken line R. The clean fluid from the processing unit

10 400 is introduced into a flow line downstream of the production wing 15 of the tree. Preferably, a connecting line 463 from the processing unit 400 is connected to a pipe 31 between the production wing and well choke 30. If there is a connection valve already provided in the pipe 31, then this can conveniently be utilised for connecting the line 463 with the pipe 31. In this case, the main bore 13 of the valve tree 12 is unavailable as it is occupied by the intervention tool 40, such that the

15 point of connection for the clean fluid to the pipe 31 is made without using the flow tube, but still preferably close to the valve tree 12.

Figure 11 shows the offshore platform 1 where the apparatus 110 is arranged with the processing unit 400 above the hatch 4b in the installation location B. The processing unit is installed as in Fig-

20 ure 9, but in this case is in an intervention mode with an intervention tool 40 being lowered into the well through the pipe section 422. The processing unit 400 is connected and operates as described in relation to Figure 10. In Figure 11 however, the pipe section 422, through which access for the intervention tool 40 is provided for accessing the well via the main bore 13 of the valve tree 12, includes both an intervention riser 422i above extending from the processing unit to connect

25 with the intervention interface above and a valve tree riser 422r extending from the valve tree 12 through the opening of the hatch 4b to the connector hub 421 of the processing unit 400.

In general, it can be appreciated that the flow tube as described above may be configured in different ways in other embodiments of the invention, but still be capable of its basic performance in al-

30 lowing the flow of clean fluid to traverse the main bore 13 of the tree 12 between the service wing inlet and production wing inlet. In the figures above, see for instance Figure 5, a fixed variant of the flow tube 17 is illustrated, where the flow tube 17 is fixed to a flange 67 which is attached to a mating flange on the service wing of the tree. When attached and in place for use, the flow tube 17 extends from the flange 67 across the main bore 13, as illustrated in Figure 5. When the flow tube is

35 to be removed, e.g. when full access to the main bore 13 is needed, the flange is disconnected and removed so as to extract the flow tube from the tree 12.

Turning to Figures 12A and 12B, a different flow tube 517 is employed instead of the fixed flow tube 17 as described above. More specifically, in Figure 12A, an embodiment of apparatus 510 for

40 processing fluid from a well is depicted, including a processing unit 516 including a de-sander

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mounted on the valve tree 12. It shows in particular a variant using a removable flow tube 517. In a mode where access to the main bore is required by other equipment, and the flow tube 17 needs to be removed from the main bore, e.g. in the intervention modes of Figures 9 or 10, the flow tube 517 can be stored in the valve tree, e.g. inside the service wing 14 as illustrated in Figure 12A. In

5 order to store the flow tube 517, a housing 565 is connected to the service wing for containing the flow tube 517 inside the valve tree 12 in a stowed position, with the service wing valve 24 closed between the housing 565 and the main bore 13. The housing 565 typically remains fixed in place to the service wing while the flow tube is in use. When the flow tube 517 is to be deployed in its use position where it straddles the main bore 13, a suitable deployment tool may be used to posi-

10 tion it. When it is to be retrieved, a retrieval tool may be used in order to retrieve (e.g. “fish”) the flow tube back into the housing 565 where the tube 517 is kept until further needed. The deployment and retrieval tools may therefore need to be deployed when the flow tube is to be deployed or retrieved, and may be removed from the area of the valve tree 12 at other times. Permanent deployment or retrieval tools are not required, which may have benefits in terms of space. As the flow

15 tube 517 can be housed within the housing on the outside of the service wing valve 24, the service wing valve 24 can be utilised to seal the main bore 13. With the flow tube removed from the main bore and contained within the housing 565, there would not be flow through the service wing valve, and a flow valve 564 in the line which could otherwise send the clean fluid from the processing unit 516 through the tree would be closed as indicated.

20

Figure 12B illustrates the apparatus 510, with the flow tube 517 deployed and inserted to bridge the main bore 13 for circulation of clean fluid from the processing unit 516 into the tree 12 through the flow tube 517 and onward downstream, the valve 564 now open.

25 In Figures 13A and 13B another variant is illustrated with a retractable flow tube 717 employed to provide for directing the flow through the tree 12. In this case, the flow tube 717 is connected to an actuator 765 which is connected onto to the service wing 14. The actuator 765 has an actuation mechanism 766 which is operable to move the flow tube 717 from a retracted position (inside the valve tree 12) as illustrated in Figure 13A into an extended, operational position as illustrated in

30 Figure 13B, and vice versa. In the operational position, the flow tube 717 reaches across the main bore 13 and can direct cleaned fluid from the de-sander 716 through the flow tube 717 and the valve tree 12 as indicated in Figure 13B, and onward downstream to the production system. In this variant, the actuator 765 and actuation mechanism 766 typically remains in place and on standby on the valve tree and can simply be activated to actuate the flow tube 717 to put it in the required

35 position, either retracted or extended, when needed.

In the above, the valve tree is described as being provided on a platform or rig. However, it should be appreciated that valve trees configured in the same manner, having a main bore accessible from the top, a service wing and a production wing, may also be found on land or subsea. The de

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sander, etc., may therefore be connected and used on a land or subsea valve trees in the same way as described above for the platform or rig tree.

While the above examples illustrate a processing unit that receives fluid from one well, it will be ap-

5 preciated that several wells may be in operation simultaneously, where the valve trees associated with the respective wells are collected together at a manifold (e.g. subsea manifold) or on a valve tree deck of a platform. The processing unit may in such cases be located at or on the valve tree of one well, but also used to receive fluid from another well, e.g. a neighbouring or an adjacent well, by routing the flow from the other well through appropriate flow lines to the processing unit.

10 The processing unit may in such cases be used both to clean the fluid of the well on which the processing unit is provided and the fluid of the neighbouring well, e.g. by combining the fluid from the two wells and leading the combined fluid into the de-sander for removal of solids. The cleaned fluid produced from the processing unit may travel downstream through the valve tree on which the processing unit is provided and/or through the valve tree of another well (e.g. the neighbouring or adja-

15 cent well), e.g. via an inserted flow tube in the relevant valve tree or trees and by appropriate flow lines between the valve trees.

Furthermore, example embodiments are described above where the valve tree supports and bears the weight of the processing unit and de-sander by way of the processing unit being connected to

20 the top of the valve tree. In other examples, the valve tree may only do so partially, for instance by providing some additional supporting means for supporting the processing unit which relieves the valve tree of the full load of the processing unit. If for example there is a deck above the valve tree, the processing unit can be held on a support on the deck so that the weight of the processing unit or de-sander is not transferred to the valve tree. This may be useful if the weight-bearing capacity

25 of the tree is limited and might be exceeded if transferring the entire weight of the processing unit to the valve tree. It will be appreciated that in examples not in accordance with the present invention, the valve tree may not bear the weight of the processing unit and de-sander.

Figure 14 illustrates a solution using a stinger 622 for guiding the flow of fluid from the well into the

30 de-sander and for guiding the cleaned flow from the de-sander through the tree 612 and downstream to the downstream processing system. This solution may be applied on rig or platformbased valve trees in accordance with the present invention. In examples not in accordance with the present invention, this solution may be applied on subsea, or land valve trees. It can be particularly useful in valve trees where there is no service wing, since it avoids access through a service

35 wing. The solution of Figure 14 by using a stinger provides an alternative means for installing the de-sander, instead of using the bridging flow tube which crosses the main bore as described in the examples above.

More specifically, in the example of Figure 14, apparatus 610 includes a processing unit 616 which

40 is mounted upon a valve tree 612. The processing unit 616 has a stinger 622 through which the

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processing unit 616 fluidly and physically connects with the valve tree 612. The stinger 662 has an outer tube 662t and an inner tube 662i. The stinger 662 penetrates into the main bore 613 of the valve tree 612 and seals between the outside of the stinger 662 and an inner surface of the main bore 613 by way of two sets of seals 667, 668. The penetrating end of the stinger 662s is

5 tubular and an inner tube 622i is inserted along the vertical main bore 613. This allows fluid from the well to flow upward inside the inner tube 662i of the stinger 662s and into the de-sanders 627a, 627b of the processing unit 616. The path of the flow to the de-sanders 627a, 627b is indicated by the broken line with arrows W. An important feature of this example is that it provides for installation of the processing unit on the valve tree and establishes the necessary flow paths without need-

10 ing access through a service wing inlet of the valve tree.

Clean fluid from the de-sanders 627a, 627b is directed into a sealed annulus in the valve tree 612 between an outside of the lower part 622s of the stinger 622s and a wall of the main bore 613 of the valve tree 612. The clean fluid may also travel via an annular space between the outer and in-

15 ner tubes 662i, 662t of the stinger 662. The path of the clean fluid is indicated by the broken line and arrows V. The clean fluid then passes out of the valve tree through the production wing bore 615 and associated valve 625. The service wing is not engaged in this set up, so this arrangement, utilising the stinger, can be applied where there is no service wing inlet available such as may be found on a subsea tree, or if a service wing of the tree is otherwise occupied.

20

The solution of Figure 14 may be convenient since the stinger can be lowered directly onto the top of a main bore of the valve tree so that both the de-sander is installed and the necessary flow path for fluid is set up for directing fluid into the de-sander and cleaned fluid back through the valve tree. Since it does not require access to the service wing, it provides a solution for valve trees where

25 there is no service wing for installing a flow tube across the vertical main bore between the service wing inlet and the production wing outlet, or if for some other reason the service wing may not be accessible. Subsea valve trees in many cases do not have a service wing inlet, often having only a horizontal production bore (“production wing”) for production fluid, and an access inlet aligned with a main bore in the tree through which equipment can access the wellbore where needed. There-

30 fore, the solution of Figure 14 may be particularly applicable and the only alternative for some subsea valve trees. In other cases such as on a rig or a platform, there may be several valve trees on the valve tree deck in relative close proximity to one another and little space for access adjacent to the tree. The Figure 14 solution may thus be useful in valve trees on platforms or rigs, even if the valve tree has a service wing. It can of course also be applied similarly to a land or a subsea valve

35 tree, even if the valve tree has a service wing, where there may also be lack of access or other reasons to prefer the stinger arrangement to insertion of a horizontal flow tube via the service wing inlet.

In general, the stinger configuration can be advantageous in that the processing unit 616 can be

40 provided and installed on the wellhead directly and ready for use, simply by guiding the stinger into

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the main bore of the tree until it abuts and sits in the correct position with the seals 667, 668 engaged. This can be beneficial in the case of subsea wells, where the wellhead is at the seabed with a subsea valve tree on the wellhead.

5 When in use as seen in Figure 14, the stinger 662 occupies space in the main bore of the tree, reducing accessibility to the well. If full diameter access is required, e.g. for performing an intervention, the inner tube 662i of the stinger can be removed from the outer tube 662t, e.g. by fishing it out on a wireline or the like. Thus, interventions can be performed by lowering intervention tools through the outer tube 662t while the processing unit 616 remains in place on the valve tree. It will

10 be appreciated that the outer tube 662t in this embodiment in effect provides a pipe section to which the de-sanders in this variant are fixed and mounted in place.

The embodiments described above may be advantageous in various ways. In particular, they allow the ability to clean well fluids very close to the valve tree, before entering downstream choke or

15 processing equipment which may be sensitive to solids exposure or the like. The apparatus can be provided space effectively and installed efficiently as a pre-provided compact unit, and may remain installed and used to clean fluid during interventions in a well where full bore access may be needed.

20 Various modifications and improvements may be made without departing from the invention herein described.

Claims

344601 16 CLAIMS

1. An assembly for an oil and gas production platform (1) or rig, the platform (1) or rig having a Christmas tree deck (2) and a hatch deck (3) above the Christmas tree deck (2),

5 the assembly comprising:

a Christmas tree (12, 612) connected to a top of a wellhead (5) on the platform (1) or rig, the Christmas tree (12, 612) located at the Christmas tree deck (3);

and being characterised in that the assembly further comprises:

a processing unit (16, 116, 216, 316, 416, 516, 616, 716) comprising at least one

10 separator (127, 227, 327a, 327b, 427a, 427b, 627a, 627b), positioned above and connected onto a top of the Christmas tree (12, 612), the Christmas tree (12, 612) bearing at least partially the weight of said separator;

wherein the separator (127, 227, 327a, 327b, 427a, 427b, 627a, 627b) is configured to be operable for receiving production fluid from at least one oil and gas

15 production well and removing solids to clean the production fluid.

2. An assembly as claimed in claim 1, wherein the Christmas tree (12, 612) has a vertical bore (13, 613) for accessing the well by an intervention tool (40) or another tool lowered on a wireline (41) or tubing from above the vertical bore (13, 613) through said

20 tree (12, 612); and the processing unit is further arranged to provide full diameter access to the vertical bore (13, 613) of the Christmas tree.

3. An assembly as claimed in claim 1 or 2, wherein the separator is a de-sander (127, 227, 327a, 327b, 427a, 427b, 627a, 627b).

25

4. An assembly as claimed in claim 3, wherein the de-sander (127, 227, 327a, 327b, 427a, 427b, 627a, 627b) has a processing tank mounted in the processing unit.

5. An assembly as claimed in claim 4, wherein the de-sander (127, 227, 327a, 327b,

30 627a, 627b) has an associated solids container (128, 228, 328a, 328b, 628a, 628b) comprising a processing tank for containing removed solids transferred from the desander in order to be later disposed of.

6. An assembly as claimed in any of claims 3 to 5, wherein the processing unit (116)

35 includes a degasser (126) for removing gas from the production fluid upstream from the de-sander (127).

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7. An assembly as claimed in any preceding claim, wherein the at least one separator comprises first and second de-sanders (327a, 327b, 427a, 427b) operable in parallel to clean the production fluid.

5

8. An assembly as claimed in any preceding claim, wherein the processing unit (116, 216, 316, 416, 616) has a vertical conduit or passageway for passage of an intervention tool (40) or other tool therethrough.

10 9. An assembly as claimed in claim 8, wherein the conduit or passageway is provided by a pipe section (122, 222, 322, 422, 622) concentric with the vertical bore (13, 613) of the Christmas tree (12, 612).

10. An assembly as claimed in claim 8 or 9, wherein the separator is a de-sander

15 (127), the de-sander (127) and a solids container (128) associated with the de-sander being arranged in the processing unit (116, 216, 316, 416) in respective positions along the vertical conduit or passageway.

11. An assembly as claimed in claim 8 or 9, wherein the separator comprises a tank

20 for cleaning the fluid which tank is elongate along the vertical conduit or passageway.

12. An assembly as claimed in any preceding claim, wherein the processing unit comprises a connector (121, 221, 321, 421) for connecting the processing unit onto the top of the Christmas tree (12).

25

13. An assembly as claimed in claim 12, wherein the connector (121) is configured to mate with a top flange of an upper bore portion of the vertical bore (13) of the Christmas tree (12).

30

14. An assembly as claimed in any preceding claim, wherein the processing unit (116, 216, 316, 416, 616) comprises a mount (129a, 229a, 329a, 429a) for mounting the separator therein.

15. An assembly as claimed in any preceding claim, wherein the processing unit

35 further comprises either or both of an emergency shut down valve (462) and a choke.

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16. A method of equipping a Christmas tree (12, 612) for processing fluid from at least one oil and gas production well using the assembly claimed in any preceding claim, the method comprising:

providing a processing unit (16, 116, 216, 316, 416, 516, 616, 716) comprising at

5 least one separator (127, 227, 327a, 327b, 427a, 427b, 627a, 627b) onto the Christmas tree (12, 612) such that the separator is at least partially supported on top of the Christmas tree;

positioning the processing unit (16, 116, 216, 316, 416, 516, 616, 716) with respect to the Christmas tree (12, 612), to position the processing unit in an operating position in

10 which the separator is operable to receive production fluid from at least one oil and gas production well and clean the production fluid.

17. A method as claimed in claim 16, which is performed to equip the Christmas tree (12, 612) on an oil and gas production platform (1) or rig, said platform or rig having a

15 Christmas tree deck (2) and a hatch deck (3) above the Christmas tree deck (2), wherein the Christmas tree (12, 612) is arranged at the Christmas tree deck (2), the method including the step of lowering the processing unit through a hatch (4b) in the hatch deck (3) onto the Christmas tree (12, 612), so as to locate the separator in place in the operating position, at least partially supported on the top of the Christmas tree (12, 612).

20

18. A method of performing an intervention operation through the vertical bore (13, 613) of the Christmas tree of the assembly of claim 2 or any of claims 3 to 15 when dependent upon claim 2, by lowering intervention equipment through the vertical bore (13, 613), while the separator (127, 227, 327a, 327b, 427a, 427b, 627a, 627b) remains in

25 place and is at least partially supported on the top of the Christmas tree (12, 612).

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