Technical field

The present invention relates generally to the processing of fluid from wells. In particular, it relates to the processing, removal, and disposal of solids such as sand and sediments from fluid such as production fluid extracted from a well, and to apparatus and methods to perform such processing on rigs, platforms, and/or onshore or subsea structures.

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 are conventionally produced by a well, driven to 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 sub- sea at the seabed, or on the well floor of a production platform.

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 reservoir 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 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 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 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.

In addition, as a reservoir depletes over time, the amount of solids in the production fluid can tend to increase. These solids typically comprise grains of rock or minerals, e.g. sand, from the geological formation of the subsurface that the wellbore penetrates. For instance, the grains of rock or minerals, e.g. sand, may come from the reservoir formation and enter the wellbore together with hydrocarbon fluid from the formation. The presence of such solids 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 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 to handle the increased production of solids. For example dedicated solids separation units such as a de-sander used on a temporary basis, in order to remove solids and in particular produced grains of formation rock or sand from the flow of production fluid before the production fluid enters the normal processing system further downstream. Use of equipment such as de-sanders or similar devices can therefore 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 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.

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 formation rock fragments 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.

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

In light of the above, according to a first aspect of the invention there is provided apparatus comprising: at least one separator for receiving fluid from at least one well and removing solids to clean the fluid. The apparatus may further comprise at least one body to which the separator is connected, for supporting and arranging the separator in position with respect to a valve tree which is connected to a wellhead. The separator may typically be arranged to be at least partially supported in use by the valve tree. The apparatus may be further configured so that when installed the apparatus and the valve tree are positioned on a common, vertical axis.

According to a second aspect of the invention there is provided apparatus configured to be installed on a structure in which an access hatch is provided for accessing a valve tree which is connected to a wellhead. The access hatch may have a vertical axis extending therethrough. The apparatus may comprise at least one separator for receiving fluid from at least one well and for removing solids to clean the fluid. The apparatus may be further configured so as to be positioned on the vertical axis.

The apparatus may be configured to fit through an opening of the access hatch. The separator, or at least one tank of the separator, may be configured to fit through an opening of the access hatch. The apparatus or part thereof may be arranged to be positioned above the access hatch when installed. The separator or part thereof may be arranged to be positioned below the access hatch when installed. The separator may be arranged to be positioned within the lateral extent of the access hatch when installed.

The apparatus may further comprise a hub or processing unit for processing fluid in which the separator may be mounted together with another component selected from any one or more of: a choke; an emergency shut down valve; and a flow line, a valve, or other equipment for operating the separator.

The body may comprise a mount for the separator and optionally another component, e.g. one of the other components of the hub. The body may be arranged to connect to the valve tree, or to a riser extending from the valve tree, for providing either or both of fluid and physical connection with the valve tree. The body may be arranged to connect to a top of the valve tree, or connect to an upper end of a vertical bore of the valve tree.

The body may comprise at least one connector for connecting with the valve tree. The connector may be arranged to connect to a top of the valve tree, or connect to an upper end of a vertical bore of the valve tree. The body may have a bore for conveying fluid from the well between the valve tree and the separator, e.g. from the valve tree to the separator. The body may comprise a pipe section. The bore may be a bore of the pipe section.

The body may be configured to attach to the valve tree so that the bore may be aligned or concentric with a vertical bore of the valve tree to allow for full diameter access to the vertical bore, e.g. for lowering equipment (e.g. a work string) through the aligned or concentric bores and into the wellbore.

The separator may be mounted so as to be offset laterally with respect to a vertical bore of the valve tree for allowing full diameter access through the vertical bore of the valve tree if required when the apparatus is installed. The full diameter access may be provided as described anywhere else herein.

The separator may be mounted to be offset laterally from the bore in the body of the apparatus so as to allow the full diameter access to be obtained via the bore in the body of the apparatus. The at least one separator may comprise first and second separators each comprising respective first and second tanks for cleaning the fluid from the well. The separator may comprise a de-sander.

The fluid from the well may be any of: production fluid; drilling fluid; well stimulation fluid; and circulation fluid.

The access hatch may be provided on a deck of the structure. The structure may be one of a subsea template; an offshore platform or rig above the sea surface; and an onshore platform. The platform or rig may be an oil and gas platform or rig, e.g. an oil and gas production platform or rig.

According to a third aspect of the invention there is provided an assembly comprising: a valve tree connected to a wellhead of a well; and apparatus. The apparatus may be as set out in any other aspect of the invention. The apparatus may be for processing fluid from at least one well. The apparatus may be a processing unit or hub as defined in relation to any aspect of the invention herein. The apparatus may comprise at least one separator for receiving said fluid from the well, and the separator may be operable for removing solids to clean the fluid.

The separator may preferably be arranged to be at least partially supported in use on a valve tree which is connected to a wellhead. More specifically, the processing unit or hub and/or the separator may be at least partially supported, optionally via a riser, on an upper end of a vertical bore of the valve tree. In this way, the valve tree may bear at least some part of the weight of the apparatus and/or the separator, when the apparatus is installed. In one embodiment, the assembly may be an assembly for an oil and gas production platform or rig. The platform or rig may have a Christmas tree deck and a hatch deck above the Christmas tree deck. In such an embodiment, the assembly may comprise a Christmas tree connected to a top of a wellhead on the platform or rig; and a processing unit or hub which may comprise at least one separator. The Christmas tree may be located at the Christmas tree deck. The separator may be positioned above and be connected to a top, or to an upper end of a vertical bore, of the Christmas tree. The Christmas tree may bear at least partially the weight of said separator. The separator may be operable for receiving production fluid from at least one oil and gas production well and removing solids to clean the production fluid. In another embodiment, the assembly may comprise: a Christmas tree connected to a top of a wellhead; and a processing unit comprising at least one separator. The Christmas tree may have a vertical bore for accessing the well by an intervention or another tool. The tool may be lowered on a wireline or tubing into and/or through said tree from a location where the tool is located above the vertical bore of the Christmas tree. The separator may be positioned above and be connected to a top, or to an upper end of a vertical bore, of the Christmas tree. The Christmas tree may bear at least partially the weight of said separator. The processing unit may be further arranged to provide full diameter access to the vertical bore of the Christmas tree. The separator may be operable for receiving oil and gas production fluid from at least one well and removing solids to clean the production fluid. Also in this embodiment, the assembly may be an assembly on an oil and gas production platform or rig. The platform or rig may have a Christmas tree deck and a hatch deck above the Christmas tree deck. The Christmas tree may be arranged at the Christmas tree deck.

The separator may comprise a de-sander. The de-sander may be a cyclonic de-sander. More specifically, the de-sander may be arranged to produce a cyclonic or rotational flow of the fluid about a vertical axis. The de-sander may comprise a tank, e.g. a processing tank. The cyclonic or rotational flow may be produced on a vertical wall of the tank of the de-sander. The flow may be obtained inside the tank of the de-sander. The flow may be produced in a region between a screen and the wall of the tank. The screen may typically be a cylindrical screen arranged vertically in the tank. During operation of the de-sander, the solids may drop out of the cyclonic or rotational flow, e.g. under the force of gravity. The fluid may be production fluid which may include hydrocarbons from a subterranean hydrocarbon reservoir. The solids may comprise formation rock particles or fragments, e.g. sand, from a subterranean formation.

The tank may be a cylinder which may be vertical. Accordingly, opposite ends of the cylinder may be arranged vertically one above the other. A cylindrical body of the cylinder may extend longitudinally between the ends. The interior of the cylindrical body of the tank may comprise a cylindrical space. In use, the flow may be produced on a vertical wall of the interior of the cylindrical body of the tank.

The solids may fall to a base of the tank. The processing unit may include a collector for collecting the solids which drop out of the cyclonic or rotational flow. The collector may comprise a tank, e.g. a processing tank, arranged below the tank of the de-sander. The solids may be transferred under gravity from the tank of the de-sander to the tank of the collector.

The de-sander may be a dynamic de-sander. The de-sander may have a rotatable body in the tank of the de-sander. The rotatable body may impart a component of force on the fluid received when rotated. The imparted component of force may facilitate to drive the fluid toward a vertical wall of the tank, e.g. urging the fluid in the flow radially outwardly toward the wall. The rotatable body may comprise at least one impeller, blade, or fin. The rotatable body may preferably be rotatable about a vertical axis. The impeller, blade, or fin may facilitate imparting the component of force for driving the fluid laterally outward toward the wall. The rotatable body may be driven to rotate by a motor. The rotatable body may be disposed on a shaft which may be coupled to the motor. The motor may operate to rotate the shaft about its longitudinal axis, for rotating the body. The shaft may be arranged with the longitudinal axis arranged vertically. The rotatable body may be fitted on an inside of the screen in the tank. The screen may have one or more openings through a wall, typically a vertical wall, of the screen. The rotatable body may drive the fluid through the opening(s) in the wall of the screen. The screen may be fixed with respect to the tank, and the rotatable body may thus rotate relative to the screen (and the tank).

The de-sander may have the tank mounted in the processing unit. The de-sander may have an associated collector or solids container, which may comprise a tank for containing removed solids transferred from the de-sander in order to be later disposed of.

The de-sander may be a first de-sander and the processing unit may further comprise a second de-sander. The second de-sander may have further features as defined above in relation to the first de-sander. For example, either or both of the first and second de-sand- ers may produce a cyclonic flow and may be a dynamic de-sander. The first and second de-sanders may be operable in parallel to clean the production fluid.

The processing unit may include a degasser comprising a processing tank, for removing gas from the production fluid upstream from a de-sander.

The processing unit may have a vertical conduit or passageway aligned with the vertical bore of valve tree. The vertical bore may be for deploying an intervention or other tool on a wireline or tubing into the valve tree. The processing unit may comprise a vertical conduit. The vertical conduit may be aligned with a vertical bore of the valve tree. The tank of the de-sander and the tank of the solids container or collector may be spaced apart in the processing unit along the conduit or passageway. The tank of the separator (e.g. de-sander) may extend longitudinally along the vertical conduit or passageway. The conduit or passageway may comprise a vertical pipe section.

In embodiments providing full bore access or full diameter access, the conduit or passageway may be arranged so that the intervention tool or other tool may be lowered from the conduit or passageway into the valve tree, such that an intervention or other tool may be inserted and may utilise or occupy the full inner diameter of the vertical bore of the valve tree. The internal diameter of the passageway or conduit may thus be equal to or exceed the internal diameter of the vertical bore of the valve tree. The intervention or other tool may then be arranged to be delivered into the wellhead in an arrangement where the main bore of the valve tree is accessible in its full diameter over its full length. The passageway or conduit and/or bore of the valve tree may then not provide any restriction to passage of the tool therethrough. Such a restriction may be considered a localised narrowing then widening of the diameter of the bore of the valve tree and/or passageway or conduit (in the direction toward the wellhead), or may be an obstacle in the middle of the bore. Such restriction may be created in particular modes of operation, e.g. by a flow tube which may be inserted fully or partially into the bore of the valve tree. The inserted flow tube may thus prevent full diameter access to the wellhead at certain times of use, but may be removed at other times to provide full diameter access.

The processing unit may comprise a connector. The connector may be for connecting the processing unit onto the top of the valve tree, or to an upper end of a vertical bore of the valve tree. The connector may thus connect the processing unit to the valve tree at the top of the valve tree or the upper end of the vertical bore of the valve tree. The connector may be configured to mate with a top flange of an upper bore portion of the vertical bore of the valve tree. The processing unit may comprise a mount for mounting the separator therein. The processing unit may further comprise either or both of an emergency shut down valve and a choke.

According to a fourth aspect of the invention there is provided a method of equipping a valve tree for processing fluid from at least one well using the apparatus as set out in any other aspect of the invention, or the assembly as set out in any other aspect of the invention.

In embodiments in which the assembly may include a processing unit, the method may comprise applying the processing unit to the valve tree such that the separator can be at least partially supported on the valve tree, whereby said valve tree may bear at least part of the weight of the separator. More specifically, the processing unit and/or the separator may be at least partially supported on an upper end of a vertical bore of the valve tree.

The method may be performed to equip the valve tree on an oil and gas production platform or rig, wherein the platform or rig may have a valve tree deck and a hatch deck above the valve tree deck, and the valve tree may be arranged at the valve tree deck. The method may then include the step of lowering the processing unit through a hatch in the hatch deck onto the valve tree, so as to locate the separator in place, at least partially supported on the top of or on the upper end of a vertical bore of the valve tree.

The method may comprise the steps of:

providing the apparatus as set out in any other aspect of the invention;

positioning the apparatus with respect to the valve tree, to position the apparatus in an operating position in which the separator is operable to receive and clean the fluid.

The method may further comprise letting the valve tree at least partially support the separator, in said operating position.

According to a fifth aspect of the invention there is provided a method of providing an assembly for processing fluid from at least one well, the assembly comprising the apparatus as set out in any other aspect of the invention and a valve tree. The assembly may be to be provided on a structure in which an access hatch may be provided for accessing the valve tree. The access hatch may have a vertical axis extending therethrough. The method may comprise the steps of: providing the apparatus as set out in any other aspect of the invention; and positioning the apparatus in an operating location in which the separator may be operable to receive and clean the fluid. In the operating location, the positioned apparatus may be positioned on the vertical axis. The method may further comprise lowering the apparatus and/or the separator through an opening of the access hatch to position the apparatus in the operating location. The apparatus may be connected in place so that the apparatus and/or the separator may be arranged within a lateral extent of the access hatch. The method may further comprise connecting the apparatus to the valve tree so as to be supported thereupon.

According to a sixth aspect of the invention there is provided a method of performing an operation, e.g. performing an intervention operation through the vertical bore of a valve tree of any of the aspects. The operation may be performed in a well while the apparatus as set out in any other aspect or as applied in any other aspect remains in place.

The intervention operation may be performed by lowering intervention equipment through the vertical bore of the valve tree. The operation may be performed with the separator in place and being at least partially supported on the top of the Christmas tree.

The operation may comprise either a well intervention operation or a drilling operation, and may include accessing the well with equipment for intervention or drilling via an access bore in communication with the wellhead, the separator being laterally offset with respect to the access bore.

According to a seventh aspect of the invention, there is provided an assembly comprising a valve tree which is connected to a wellhead and apparatus comprising at least one separator for receiving fluid from at least one well and removing solids to clean the fluid, wherein the apparatus and the valve tree are positioned on a common, vertical axis.

According to an eighth aspect of the invention there is provided an assembly comprising: at least one valve tree; and

apparatus comprising at least one separator for receiving fluid from at least one well and removing solids to clean the fluid. At least part of the apparatus may be located in a region between a valve tree deck on which the valve tree may be provided, and a hatch deck, which may be adjacent to and overlie the valve tree deck. The hatch deck may be configured for accessing the valve tree through at least one hatch.

According to a ninth aspect of the invention, there is provided a method of processing fluid from at least one well, the method comprising the steps of: providing at least one separator which is arranged to receive the fluid from the well downstream from at least one wellhead; and

using the separator to remove solids from the fluid, to produce a cleaned fluid which travels downstream on a flow path from the separator through either or both of: a valve tree on the wellhead from which the separator receives the fluid; and a valve tree on another wellhead.

In a preferred embodiment, the well may have a wellhead, and a Christmas tree may be disposed on the wellhead, and the method may comprise the steps of:

providing at least one separator, receiving the production fluid in the separator downstream from the wellhead and the Christmas tree, the production fluid travelling through a Christmas tree on said wellhead to the separator; and

using the separator to remove solids from the production fluid, to produce a cleaned production fluid which may travel downstream on a flow path from the separator through either or both of: the Christmas tree on said wellhead from which the separator receives the production fluid; and a production Christmas tree on another wellhead.

The method may further include using the separator to remove gas from the fluid in order to produce the cleaned fluid. The method may further comprise cleaning the removed solids to remove contaminants so as to allow disposal. The cleaned fluid from the separator may travel through a well choke operable to control extraction of the fluid from the well. The flow path may be provided via a tube inserted into the valve tree, e.g. the Christmas tree. At least one tank of the separator may be mounted above the valve tree so as to be supported thereupon.

According to a tenth aspect of the invention there is provided apparatus for processing fluid from at least one well, the apparatus comprising:

at least one separator for receiving the fluid from the well downstream from at least one wellhead, the separator being operable for removing solids from the fluid for producing a cleaned fluid; and

a flow path for the cleaned fluid to travel downstream from the separator through either or both of: a valve tree on the wellhead from which the separator receives the fluid; and a valve tree on another wellhead.

In a preferred embodiment, the well may have a wellhead and a Christmas tree may be disposed on the wellhead, and the apparatus may comprise: at least one separator for receiving the production fluid from the well downstream from the wellhead and the Christmas tree, wherein the production fluid, in use, may travel to the separator through a Christmas tree on the wellhead, the separator being operable for removing solids from said fluid for producing a cleaned production fluid; and

a flow path for the cleaned production fluid to travel downstream from the separator through either or both of: the Christmas tree on said wellhead from which the separator receives the production fluid; and a production Christmas tree on another wellhead.

The flow path may be obtained by a tube inserted into the valve tree.

The valve tree may have a bore through which fluid can travel from the wellhead to the separator. The bore may be a vertical bore. The tube may comprise a bridge tube arranged to bridge radially across the bore of the valve tree. The cleaned fluid from the separator may pass through the bridge tube to exit the valve tree.

The valve tree may have a service wing and a production wing. The bridge tube may be inserted to span between respective bores of the service and production wings for allowing the cleaned fluid from the separator to pass through the bridge tube and exit the valve tree from the production wing.

The bridge tube may be removed from operation if required, e.g. for allowing full diameter access to the well through an access bore of the valve tree.

The apparatus may further comprise an actuator configured to be mounted to the valve tree for inserting the bridge tube into the access bore for operation, or retracting the bridge tube from operation so as not to obstruct the access bore. The access bore may be a vertical bore of the tree.

The valve tree may have a vertical access bore for accessing the well from above. The tube may be inserted into the access bore of the tree along the access bore. The production fluid to be cleaned may travel through the tube to the separator. The apparatus may further comprise a stinger which may include the tube. The stinger may be arranged to deliver the tube into position so as to insert the tube into the vertical access bore of the tree. Said tube may be an inner tube of the stinger and may be removable from an outer tube of the stinger. This may facilitate removal of the inner tube from the valve tree, and/or may facilitate allowing full diameter access to the access bore of the valve tree through the outer tube. The inner tube may be arranged to be fished out of the stinger by deploying fishing equipment.

The apparatus may further comprise a body having a bore. The body may be arranged to mate with the valve tree so that the bore may be aligned with a bore of the valve tree for fluid from the well to travel to the separator through the bore. The body may comprise a pipe section. The bore may be a bore of the pipe section.

The separator may be mounted to the body. The body may comprise a riser, or may be arranged to connect with a riser, the riser being connected to the valve tree so that fluid from the well can travel through a section of the riser, to the separator to clean the fluid. The riser may be an intervention riser, and the apparatus may be configured to allow access to the well through the riser to perform an intervention, in an intervention mode, if desired.

The apparatus may further comprise a tube of a stinger arranged along a bore of the valve tree or a tube for bridging across a bore of the valve tree, wherein the tube may be removable out of operation, to allow an intervention to be performed with full diameter access through the bore in the intervention mode.

The apparatus may further comprise either or both of an emergency shut down valve and a well choke along the flow path downstream from the separator.

The apparatus may further comprise a hub or processing unit, in which may be mounted any one or more of:

the separator and/or at least one tank thereof; an emergency shut down valve; a well choke; and at least one connecting body, e.g. a connector. The connecting body or connector may be for mating with the valve tree, e.g. for either or both conveying fluid from the well to the separator and supporting at least partially the weight of the hub or processing unit or separator upon the valve tree. The hub or processing unit may be as described anywhere else herein.

The processing unit or hub and/or the separator may be supported on the valve tree as described anywhere else herein. For instance, the processing unit or hub and/or the separator may be at least partially supported, optionally via a riser, on an upper end of a vertical bore of the valve tree. The separator may comprise a cyclonic or dynamic separator. The separator may comprise a de-sander. The de-sander may be as described anywhere else herein, e.g. it may be a cyclonic de-sander.

The fluid may be any of: production fluid; drilling fluid; well stimulating fluid; and circulation fluid. The production fluid may comprise hydrocarbons recovered from the subsurface of the earth, e.g. from a subsurface oil and gas reservoir. The production fluid may comprise oil and/or gas from the reservoir. The production fluid may include the solids entrained and carried in the fluid in a flow from the wellbore toward the surface. At the surface, the production fluid may pass through the production wellhead, and then through the valve tree connected to the top of the production wellhead.

The solids may be as described anywhere else herein. For example, the solids may comprise particles, fragments, or grains of rock or minerals e.g. sand from the subsurface formation penetrated by the wellbore. The particles, fragments, or grains of rock may be carried with a flow of hydrocarbon fluid.

The de-sander may operate to separate solids other than sand. Typically, the solids which may be separated from the production fluid by the de-sander may include sand or may include particles which have the same or similar characteristic to that of sand, such as the same or similar class of grain size, density, or mineralogical composition. In other words, the de-sander may cause other particles which are of same or similar character as sand to separate out.

According to an eleventh aspect of the invention there is provided a method of processing fluid from at least one well, the method comprising the steps of:

(a) providing at least one separator arranged to receive fluid from the well; and

(b) removing solids from the fluid using the separator, to produce cleaned fluid upstream of a choke for the well from which fluid is received or for another well.

According to a twelfth aspect of the invention there is provided apparatus for processing fluid from at least one well, the apparatus comprising:

at least one separator for receiving said fluid from the well, the separator being operable for removing solids from the fluid for producing cleaned fluid; and

a flow path for the cleaned fluid to travel downstream via a choke for the well from which fluid is received or for another well. The fluid from the well may therefore not pass through the choke before the fluid has been cleaned by use of the separator. The choke may preferably operate on the cleaned fluid. The choke may operate to control the flow and/or pressure in the wellbore. The choke may typically not operate on the fluid from the well before it has been cleaned by the separator.

According to a thirteenth aspect of the invention, there is provided apparatus comprising at least one separator arranged to be at least partially supported in use by a valve tree which is connected to a wellhead, the separator being operable for receiving fluid from at least one well and removing solids to clean the fluid. In this way, the valve tree may bear at least some part of the weight of the apparatus and/or the separator, when the apparatus is installed.

According to a fourteenth aspect of the invention, there is provided a method of using the apparatus as set out in relation to any aspect herein, the method comprising the steps of: providing the flow path; and

processing fluid using the apparatus by:

receiving the fluid in the separator;

operating the separator to remove solids from the fluid to produce cleaned fluid; and

letting the cleaned fluid from the separator travel downstream via the provided flow path.

Preferably, the apparatus may be used to process fluid from the well which may have a wellhead and a valve tree, e.g. a Christmas tree, disposed on the wellhead. The fluid may be received in the separator downstream from the wellhead and the valve tree. The production fluid may travel through the valve tree on the wellhead to the separator. The valve tree may comprise a Christmas tree, e.g. as described anywhere herein. The fluid may comprise production fluid. The cleaned fluid may travel downstream on the flow path through the valve tree on the wellhead from which the separator receives the fluid and/or a production Christmas tree of another wellhead.

The flow path may be provided by inserting a tube into the valve tree. The tube may be a flow tube. The tube may be inserted by inserting a stinger into a vertical bore of the valve tree. The tube may be inserted by inserting a bridge tube across a bore of the valve tree. The fluid may be received in the separator by opening a valve to direct the fluid from the valve tree to the separator. The fluid may travel downstream by opening an exit line from the separator.

The method may further comprise:

halting the processing of the fluid;

removing the flow path to allow full bore access through a vertical bore of the valve tree; and

performing an intervention or drilling operation in the well by delivering equipment through the vertical bore and into the well while the separator remains in place.

The flow path may be removed by removing or moving an inserted tube from the vertical bore of the valve tree, and wherein the equipment may be delivered into the well via the vertical bore.

The method may further comprise, after the intervention or drilling operation has been performed and the equipment has been removed, re-establishing the flow path for cleaned fluid to travel downstream from the separator; and re-commencing the processing of fluid from the well using the separator.

The valve tree may be as described anywhere else herein. The well choke may be as described anywhere else herein. 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).

In another aspect, there is provided a hub or a processing unit for processing fluid from at least one well, the hub or processing unit being configured to be connected to a valve tree on a wellhead and comprising at least one separator for removing solids to clean the fluid. The hub or processing unit may be configured to be connected to a top of the valve tree or an upper end of a vertical bore of the valve tree. The hub or processing unit may comprise at least one connector. The connector may comprise a flange for mating with a complementary flange of a vertical bore portion of the valve tree. The connector may be provided on a body to which the separator may be mounted and supported, for structurally supporting the separator upon the valve tree, e.g. on a top of the valve tree and/or an upper end of a vertical bore of the valve tree. The connector and/or the body may comprise a throughbore arranged to align with a bore of the valve tree for fluidly connecting the valve tree with the separator when connected to the valve tree, e.g. when connected by the flanges.

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 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 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 to the accompanying drawings, in which:

Figure 1 is schematic representation of an assembly comprising apparatus for pro- cessing 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 apparatus 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 l-l;

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;

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 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 according 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 1 1 is a schematic representation of apparatus for processing fluid from a well in an intervention mode according to another embodiment of the invention;

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 separator and a removable flow tube, wherein the flow tube of Figure 12A is in an 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;

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;

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 of the invention;

Figure 15 is a perspective part-sectional representation of apparatus for processing fluid from a well according to another embodiment; and

Figure 16 is a perspective part-sectional representation of the apparatus of Figure 15 using an inserted flow tube in the valve tree for facilitating the supply of production fluid to the de-sander and passage of cleaned production fluid downstream away from the de-sander.

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 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.

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) 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.

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 as described hereinabove.

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.

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 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 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 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.

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.

In another example as illustrated in Figure 4, the apparatus 10 has a processing unit 1 16 in place of the processing unit 16 described above. The processing unit 1 16 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.

In particular, the processing unit 1 16 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 1 16 includes a pipe section 122 (constituting a body with a throughbore) provided with a connector 121 for rigidly connecting the processing unit to the top of the valve tree 12. The interior of the pipe section 122 is 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 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 1 16. 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. 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 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 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.

The solids which are separated out by the de-sander 127 may selectively be disposed from the de-sander 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.

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. 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).

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 1 16 are denoted with the same reference numerals but incremented by one hundred, and may not be explicitly described again here.

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.

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.

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 disposed 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 1 16 or 216 are denoted with the same reference numerals but incremented by two 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 provided 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 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.

Referring now to Figure 7, apparatus 1 10 for processing fluid from a well is installed on the offshore platform 1 . The apparatus 1 10 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.

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 occupies 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.

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.

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 controllable 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 the downstream processing system 50 without going via the normal well choke 30, or without needing to use the well choke 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.

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 to either side of the pipe section 422. The pipe section 422 is provided centrally, and provides an 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 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 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 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. Turning to Figure 10, the apparatus 1 10 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 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 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 embodiments 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 process the returning fluid from the annulus, e.g. to remove solids from the fluid. Clean fluid, without 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 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 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 con- nected 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 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 1 1 shows the offshore platform 1 where the apparatus 1 10 is arranged with the processing unit 400 above the hatch 4b in the installation location B. The processing unit is installed as in Figure 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 1 1 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 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 being capable of its basic performance in allowing 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 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 processing fluid from a well is depicted, including a processing unit 516 including a de-sander 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 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 position 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 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.

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.

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 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 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-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 appreciated 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. 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 adjacent 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 the top of the valve tree. It will be appreciated that in other embodiments, the valve tree may not bear the weight of the processing unit and de-sander, or 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 of the tree is limited and might be exceeded if transferring the entire weight of the processing unit to the valve tree.

Figure 14 illustrates a solution using a stinger 622 for guiding the flow of fluid from the well into the 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 also be applied on subsea, land, or rig or platform based valve trees. It can be particularly useful in valve trees where there is no service wing, since it avoids access through a service 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 is mounted upon a valve tree 612. The processing unit 616 has a stinger 622 through which the 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 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 needing 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 inner 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.

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

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 be appreciated 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.

Figures 15 exemplifies in more detail how a processing unit 816 or hub may be configured and supported on the valve tree 812 in practice. This manner of connecting the processing unit 816 may be adopted in any of the embodiments described above. The processing unit 816 includes components as described in relation to Figure 6. The processing unit 816 has two de-sanders 827a, 827b (separators) and respective solids collectors 828a, 828b. The de-sanders 827a, 827b can operate in parallel to remove solids from the hydrocarbon production fluid from a producing oil and gas reservoir during hydrocarbon production. The pipe section 822 is connected to a top of the valve tree 812, on an upper end of a vertical bore of the tree 812. A connector 821 at a lower end of the pipe section mates to a flange at the top of the valve tree 812 to securely and sealingly connect the end of the pipe section 821 onto the top of the valve tree. The weight of the processing unit is transmitted through the pipe section to the valve tree 812.

In other embodiments, a vertical riser is connected to the top of the valve tree 812 and the pipe section 822 is connected to an upper end of the riser. Alternatively, the pipe section 822 may be a riser having a length so that when connected to a tree, the tanks of the processing unit are spaced vertically apart from the top of the valve tree by a desired distance, e.g. greater than that indicated by Figure 15.

As can be seen, each de-sander 827a, 827b comprises a tank 880a, 880b and each solids collector 828a, 828b comprises a tank 890a, 890b for collecting and containing the removed solids. The tanks are paired up so that the tanks 880a, 890a associated with the separation of the de-sander 827a are positioned in different locations, one above the other, along the pipe section 822. The tanks 880b, 890b associated with the de-sander 827b are similarly arranged in respective positions along the pipe section 822, one above the other, on the other side of the pipe section 822. Furthermore, the tanks 880a, 880b, 890a, 890b are arranged as upright cylinders. In other variants, the cylinders may be made longer vertically to increase their capacity without impacting on the radial footprint, or in yet further variants additional tanks e.g. de-sander and/or solids collector tanks, may be added along the pipe section, without increasing the radial footprint. Further tanks may also be placed in other locations around the circumference of the pipe section 822 without expanding a maximum diameter.

As seen in Figure 15 production fluid from the wellhead, indicated by arrows R, travels through the valve tree 812, through the pipe section 822, and is then received by the de- sanders 827a, 827b.

The cleaned production fluid from the de-sanders 827a, 827b indicated by arrows P, travels downstream from the de-sander through production flow lines for onward processing and refining, free from sand or other rock fragments from the subsurface formations. The provision of the processing unit 816 on the valve tree 812 can thus relieve the downstream flow line components from abrasion and wear as typically can be a problem in late field development scenarios. Production rates may therefore be increased as a result.

Although not explicitly illustrated in Figure 15, it can be appreciated that the cleaned production fluid P may follow a flow path through the tree, e.g. provided by inserting a tube into the bore of the tree, such as a bridge tube which crosses the vertical main bore from the service to the production wing or a stinger tube inserted into and parallel with the main bore. Alternatively, the cleaned production may pass through a tube which is simply connected to the production line at a convenient location close to the valve tree, e.g. where there is an existing access point.

Figure 15 illustrates components of the de-sander 827a in the interior of the tank 880a. The de-sanders (constituting separators) of any of the embodiments described above may be configured similarly.

The de-sander 827a (a separator) is configured to produce a fluid cyclone inside the tank 827a, so that when the production fluid enters the tank, the de-sander sets the production fluid in motion in a cyclonic flow. This may be done in various. In the example of Figure 15, has a rotatable body, e.g. a fin or impeller, inside the tank 880a which engages the production fluid and rotates to impart a rotational force on the production fluid. The production fluid enters the tank 880a at an upper end. The rotational force urges the fluid radially outward toward the wall of the tank, while at the same time being subject to gravity, providing a cyclonic or rotational flow as indicated by arrows C. The interior of the tank 880 is in the form of a cylindrical chamber. This separation of the solids in the production fluid have a different mass or density to liquid or gas components, and by virtue of this fact they are affected to different degrees by the rotational and gravitational force components, so that they separate out. The solids, i.e. rock fragments or particles of minerals, sand, etc produced from the reservoir formation, drop out of the flow and fall to the bottom of the tank 880a and collect in the tank 890b of the solids collector 828a. The liquid component or fluid combination of liquid and gas may pass onward downstream through an outlet in the wall near an upper end of the tank 880a, and constitutes cleaned production fluid which then travels away downstream as indicated by arrows P.

The rotatable body, e.g. fin or impeller (not shown) is disposed inside a cylindrical screen 882 in the tank. The body is mounted to a vertical shaft 884 inside the tank 880. The shaft is connected to a motor 886 which operates to turn the shaft 884 about its long axis. By operation of the motor 886 therefore the rotatable body is rotated about a vertical axis inside the screen 882, at a speed which provides the necessary impetus to the production fluid being received in the tank to knock out the solids. The production fluid is driven outward toward the wall of the screen, through openings in the screen, and into the region between an outside of the screen and the wall of the tank, where the production fluid flows as indicated by arrows C, and the solids fall to the bottom of the tank.

The above represents a dynamic de-sander technique where the cyclonic flow is actively enhanced by operating the rotational device using the motor. The de-sander described in WO03099448 (Arefjord) is another example of a cyclonic, dynamic de-sander. It may be appreciated that cyclonic flow may be obtained in other ways, e.g. by jetting the production fluid to drive the production fluid from a tangential inlet around a curved inner wall of a cylindrical chamber at sufficient and appropriate velocity. This may provide a cyclonic flow without use of the actively rotated rotational body driven by the motor.

Figure 16 is an implementation of the same arrangement as Figure 15 with a specific flow path solution for directing the cleaned production fluid P away from the de-sanders 827a, 827b through an inside of the valve tree 812. In this case, a flow tube 862 is inserted into the vertical main bore of the valve tree 812. The flow path is similar to that created in Figure 14. An upper end of the flow tube is positioned inside the pipe section 822 and the lower end of the flow tube 862 is positioned inside the main bore of valve tree 812 below the production wing and service wing bores. The unprocessed production fluid R passes into the lower end of the flow tube, through the flow tube 862, and exits the flow tube 862 at the upper end. The production fluid R is then received in the de-sanders 827a, 827b which operate as described above. The cleaned production fluid P returns on a flow path between an outside of the flow tube 862 and a wall of the interior of the valve tree 812. In each of the examples of Figures 4 to 1 1 and 14 to 16, full diameter access can be provided to the valve tree. In some of these examples, it is necessary to remove the flow tube used for providing the flow path for the cleaned production fluid, in order to obtain the full diameter access. The flow tube (see the stinger in Figure 14) may be removed on a temporary basis while the processing unit remains installed, so that an intervention operation or other operation which may be reliant upon the ability to have full diameter access can be performed. With reference to the example of Figures 15 and 16 therefore, the arrangement in Figure 15 illustrates a configuration of full bore access whereas in Figure 16 there is not full diameter access due to the presence of the flow tube 862. By providing full diameter access, an intervention string can be placed in the passageway (in this example inside the pipe section 862) and be lowered from a location above the valve tree 812, into and through the vertical bore of the valve tree, unhindered by any restrictions in the passageway or in main bore of the valve tree. Therefore, the intervention string may have a diameter which is equal to the inner diameter of the main bore of the valve tree (subject to tolerances of fit), and yet be allowed to pass into and through the valve tree 812. The passageway in the pipe section 862 may therefore have an internal diameter which is greater or equal to that of the valve tree over the entire part of its length which will be exposed to the maximum diameter of the intervention string. The same functionality can be provided in the embodiments of Figures 4 to 1 1 and 14 to 16. Such a configuration is typically termed full bore access, and can be an important feature to avoid having to remove processing equipment to perform well intervention, and let the processing unit 816 stay in place. This may allow an intervention to be performed efficiently and production to be quickly resumed afterwards. In Figure 16, access to the wellbore may advantageously be obtained albeit not full bore, through the flow tube while the flow tube 862 remains inserted. The interior passageway of the flow tube 862 is of a smaller diameter than the valve tree and in effect is a restriction, but this may not critical in specific applications.

In any of the examples herein, the production fluid may comprise hydrocarbons e.g. oil and gas from an oil and gas reservoir in the subsurface, and the solids which are removed by the separator may comprise grains or particles of rock or sand as may typically enter the wellbore in the far reaches of the wellbore together with the hydrocarbons from the reservoir. In all examples also, the valve tree may be connected to the top of the wellhead so as to be supported upon the wellhead.

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

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