Patent Publication Number: US-11391110-B2

Title: Method and apparatus for oil and gas operations

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. Utility patent application Ser. No. 16/212,415, filed Dec. 6, 2018 and entitled METHOD AND APPARATUS FOR OIL AND GAS OPERATIONS, which is a continuation of U.S. Utility patent application Ser. No. 14/379,277, filed Aug. 15, 2014 (now U.S. Pat. No. 10,174,575) and entitled METHOD AND APPARATUS FOR OIL AND GAS OPERATIONS, which is a National Stage Application of PCT/GB2013/050364, filed Feb. 15, 2013 and entitled METHOD AND APPARATUS FOR OIL AND GAS OPERATIONS, which designates the United States and claims the priority of GB patent application GB1202581.3, filed on Feb. 15, 2012; the entire disclosures of which are each incorporated herein by reference. 
    
    
     METHOD AND APPARATUS FOR OIL AND GAS OPERATIONS 
     The present invention relates to methods and apparatus for oil and gas operations, in particular to methods and apparatus for fluid intervention in oil and gas production or injection systems. 
     The invention has particular application to subsea oil and gas operations, and aspects of the invention relate specifically to methods and apparatus for fluid intervention in subsea oil and gas production and injection infrastructure. 
     BACKGROUND TO THE INVENTION 
     In the field of oil and gas exploration and production, it is common to install an assembly of valves, spools and fittings on a wellhead for the control of fluid flow into or out of the well. A Christmas tree is a type of fluid manifold used in the oil and gas industry in surface well and subsea well configurations and have a wide range of functions, including chemical injection, well intervention, pressure relief and well monitoring. Christmas trees are also used to control the injection of water or other fluids into a wellbore to control production from the reservoir. 
     There are a number of reasons why it is desirable to access a flow system in an oil and gas production system. In the context of this specification, the term “fluid intervention” is used to encapsulate any method which accesses a flow line, manifold or tubing in an oil and gas production, injection or transportation system. This includes (but is not limited to) accessing a flow system for fluid sampling, fluid diversion, fluid recovery, fluid injection, fluid circulation, fluid measurement and/or fluid metering. This can be distinguished from full well intervention operations, which generally provide full (or near full) access to the wellbore. Full well intervention processes and applications are often technically complex, time-consuming and have a different cost profile to fluid intervention operations. It will be apparent from the following description that the present invention has application to full well intervention operations. However, it is an advantage of the invention that full well intervention may be avoided, and therefore preferred embodiments of the invention provide methods and apparatus for fluid intervention which do not require full well intervention processes. 
     International patent application numbers WO00/70185, WO2005/047646, and WO2005/083228 describe a number of configurations for accessing a hydrocarbon well via a choke body on a Christmas tree. 
     Although a choke body provides a convenient access point in some applications, the methods of WO00/70185, WO2005/047646, and WO2005/083228 do have a number of disadvantages. Firstly, a Christmas tree is a complex and carefully-designed piece of equipment. The choke performs an important function in production or injection processes, and its location on the Christmas tree is selected to be optimal for its intended operation. Where the choke is removed from the choke body, as proposed in the prior art, the choke must be repositioned elsewhere in the flow system to maintain its functionality. This compromises the original design of the Christmas tree, as it requires the choke to be located in a sub-optimal position. 
     Secondly, a choke body on a Christmas tree is typically not designed to support dynamic and/or static loads imparted by intervention equipment and processes. Typical loads on a choke body in normal use would be of the order of 0.5 to 1 tonnes, and the Christmas tree is engineered with this in mind. In comparison, a typical flow metering system as contemplated in the prior art may have a weight of the order of 2 to 3 tonnes, and the dynamic loads may be more than three times that value. Mounting a metering system (or other fluid intervention equipment) on the choke body therefore exposes that part of the Christmas tree to loads in excess of those that it is designed to withstand, creating a risk of damage to the structure. This problem may be exacerbated in deepwater applications, where even greater loads may be experienced due to thicker and/or stiffer components used in the subsea infrastructure. 
     In addition to the load restrictions identified above, positioning the flow intervention equipment on the choke body may limit the access available to large items of process equipment and/or access of divers or remotely operated vehicles (ROVs) to the process equipment or other parts of the tree. 
     Furthermore, modifying the Christmas tree so that the chokes are in non-standard positions is generally undesirable. It is preferable for divers and/or ROV operators to be completely familiar with the configuration of components on the Christmas tree, and deviations in the location of critical components are preferably avoided. 
     Another drawback of the prior art proposals is that not all Christmas trees have chokes integrated with the system; approaches which rely on Christmas tree choke body access to the flow system are not applicable to these types of tree. 
     It is amongst the objects of the invention to provide a method and apparatus for accessing a flow system in an oil and gas production system, which addresses one or more drawbacks or disadvantages of the prior art. In particular, it is amongst the objects of the invention to provide a method and apparatus for fluid intervention in an oil and gas production system, which addresses one or more drawbacks of the prior art. An object of the invention is to provide a flexible method and apparatus suitable for use with and/or retrofitting to industry standard or proprietary oil and gas production manifolds, including Christmas trees. 
     It is an aim of at least one aspect or embodiment of the invention to provide an apparatus which may be configured for use in both a subsea fluid injection operation and a production fluid sampling operation. 
     Further objects and aims of the invention will become apparent from the following description. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided an apparatus for accessing a flow system in a subsea oil and gas production system, the apparatus comprising: 
     a body defining a conduit therethrough; 
     a first connector for connecting the body to the flow system; 
     a second connector for connecting the body to an intervention apparatus; 
     wherein, in use, the conduit provides an intervention path from the intervention apparatus to the flow system. 
     The apparatus is preferably a fluid intervention apparatus, which may be a fluid intervention apparatus for fluid sampling, fluid diversion, fluid recovery, fluid injection, fluid circulation, fluid measurement and/or fluid metering. 
     Preferably, the apparatus is an access hub which is configured for connection to the flow system. The access hub may be configured to be connected to an external opening on the flow system. For example, the access hub may be configured to be connected to a flange of the flow system. The flow system may comprise a blind flange, removal of which provides a flange connection point for the access hub. 
     Where the flow system comprises a subsea Christmas tree, the external opening may be downstream of a wing valve of the Christmas tree. 
     The external opening may be a flowline connector, such as a flowline connector for a jumper flowline. The apparatus may comprise a third connector for connecting the apparatus to a downstream flowline such as a jumper flowline. Therefore the apparatus may be disposed between a flowline connector and a jumper flowline, and may provide a flow path from the flow system to the jumper flowline, and may also establish an access point to the flow system, via the conduit and the first connector. 
     A flowline connector for a jumper flowline is a preferred location for the connection of the access hub. This is because it is displaced from the Christmas tree sufficiently to reduce associated spatial access problems and provides a more robust load bearing location compared with locations on the Christmas tree itself (in particular the choke body). However, it is still relatively near to the tree and the parts of the flow system to which access is required for the intervention applications. 
     The apparatus may provide a further connector for connecting the body to an intervention apparatus, which may be axially displaced from the second connector (in the direction of the body). Therefore the apparatus may provide a pair of access points to the flow system, which may facilitate certain applications including those which require fluid circulation and/or sampling. 
     In one embodiment, the access hub is configured for connection to an external opening of a choke body, which may be on a side of the choke body. Preferably in this embodiment, the access hub is configured to be connected to the choke body without interfering with the position or function of the choke (i.e. the choke may remain in situ in the choke body). 
     Preferably, the access hub is configured to be connected to a flowline at a location displaced from a choke of the flow system. The access hub may be configured to be connected to the flow system at a location selected from the group consisting of: a jumper flowline connector; downstream of a jumper flowline or a section of a jumper flowline; a Christmas tree; a subsea collection manifold system; subsea Pipe Line End Manifold (PLEM); a subsea Pipe Line End Termination (PLET); and a subsea Flow Line End Termination (FLET). 
     In embodiments of the invention, the apparatus is configured to provide access to the production bore or the annulus of Christmas tree directly (i.e. without relying on access through the production wing or annulus wing). In one such implementation, the apparatus comprises a tree cap hub, and the first connector connects the body to a production bore of a Christmas tree. Preferably, the intervention apparatus comprises a fluid injection apparatus. 
     The tree cap hub may comprise an axial bore extending from an opening to the production bore to a top opening of the tree cap hub. The apparatus may be provided with a pressure cap, which may seal the top opening. The apparatus may comprise a debris cap and/or insulation cap. Conveniently, the apparatus may be deployed and left in situ on the subsea Christmas tree. 
     Alternatively, the apparatus may comprise a tree mandrel hub, and the first connector is configured to be connected to an annulus bore of a Christmas tree. The tree mandrel hub may comprise a bore extending from an opening to the annulus bore to a top opening of the tree mandrel hub. The bore may comprise a first axial portion extending from the opening to the annulus bore, a second axial portion extending from the top opening, and a radial portion joining the first and second axial portions. The apparatus may be provided with a pressure cap, which may seal the top opening. The apparatus may comprise a debris cap and/or insulation cap. Conveniently, the apparatus may be deployed for a subsea intervention operation or series of operations and recovered to surface. Preferably, the intervention apparatus comprises a fluid injection apparatus. 
     According to a second aspect of the invention, there is provided a subsea oil and gas production system comprising: 
     a subsea well and a subsea flow system in communication with the well; and an access hub; wherein the access hub comprises a first connector connected to the subsea flow system; 
     a second connector configured to be connected to an intervention apparatus; and wherein a conduit between the first and second connectors provides an intervention path from the intervention apparatus to the subsea flow system. 
     The access hub may be connected to the flow system at a location selected from the group consisting of: a jumper flowline connector; downstream of a jumper flowline or a section of a jumper flowline; a Christmas tree; a subsea collection manifold system; a subsea Pipe Line End Manifold (PLEM); a subsea Pipe Line End Termination (PLET); and a subsea Flow Line End Termination (FLET). 
     Where the flow system comprises a subsea Christmas tree, the external opening may be downstream of a wing valve of the Christmas tree. 
     The external opening may be a flowline connector, such as a flowline connector for a jumper flowline. The apparatus may comprise a third connector for connecting the apparatus to a downstream flowline such as a jumper flowline. Therefore the apparatus may be disposed between a flowline connector and a jumper flowline, and may provide a flow path from the flow system to the jumper flowline, and may also establish an access point to the flow system, via the conduit and the first connector. 
     Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa. 
     According to a third aspect of the invention there is provided a method of performing a subsea intervention operation, the method comprising: 
     providing a subsea well and a subsea flow system in communication with the well; 
     providing an access hub on the subsea flow system, the access hub comprising a first connector connected to the subsea flow system and a second connector for an intervention apparatus; 
     connecting an intervention apparatus to the second connector; 
     accessing the subsea flow system via an intervention path though a conduit between the first and second connectors. 
     Preferably the access hub is pre-installed on the subsea flow system and left in situ at a subsea location for later performance of a subsea intervention operation. The intervention apparatus may then be connected to the pre-installed access hub and the method performed. 
     Preferably the method is a method of performing a fluid intervention operation. The method may comprise fluid sampling, fluid diversion, fluid recovery, fluid injection, fluid circulation, fluid measurement and/or fluid metering. 
     The method may be a method of performing a well scale squeeze operation. 
     The method may comprise performing a well fluid sampling operation. A preferred embodiment of the invention comprises: (a) performing a fluid injection operation; and (b) performing a well fluid sampling operation. Preferably the fluid injection operation and the well fluid sampling operation are both carried out by accessing the subsea flow system via the intervention path of the access hub. 
     Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention or their embodiments, or vice versa. 
     According to a fourth aspect of the invention there is provided an access hub for a flow system in a subsea oil and gas production system, the access hub comprising: 
     a body defining a conduit therethrough; 
     a first connector for connecting the body to a jumper flowline connector of the flow system; a second connector for connecting the body to an intervention apparatus; 
     and a third connector for connecting the apparatus to a jumper flowline; 
     wherein, in use, the conduit provides an intervention path from the intervention apparatus to the flow system. 
     Preferably, the subsea flow system comprises a Christmas tree, and the jumper flowline connector is production wing flowline connector of the Christmas tree. 
     Embodiments of the fourth aspect of the invention may include one or more features of the first to third aspects of the invention or their embodiments, or vice versa. 
     According to a fifth aspect of the invention there is provided a subsea oil and gas production system comprising: 
     a subsea well; a subsea Christmas tree in communication with the well; a jumper flowline and an access hub; 
     wherein the access hub comprises a first connecter connected to a flowline connector of the Christmas tree, a second connector for connecting the body to an intervention apparatus, and a third connector connected to the jumper flowline; and wherein a 
     a conduit between the first and second connectors provides an intervention path from the intervention apparatus to a production bore of the subsea Christmas tree. 
     Embodiments of the fifth aspect of the invention may include one or more features of the first to fourth aspects of the invention or their embodiments, or vice versa. 
     According to a sixth aspect of the invention there is provided an access hub for a subsea Christmas tree, the access hub comprising: 
     a tree cap comprising a tree cap connector configured to be connected to a production bore of the subsea Christmas tree and an upper connector for connecting the tree cap to an intervention apparatus; 
     wherein, in use, a conduit between the tree cap connector and the upper connector provides an intervention path from an intervention apparatus to the production bore of the subsea Christmas tree. 
     Preferably, the tree cap comprises a pressure cap. The tree cap may therefore be pre-installed on the Christmas tree and left in situ at a subsea location for later performance of a subsea intervention operation. 
     Embodiments of the sixth aspect of the invention may include one or more features of the first to fifth aspects of the invention or their embodiments, or vice versa. 
     According to a seventh aspect of the invention, there is provided a subsea oil and gas production system comprising: 
     a subsea well; a subsea Christmas tree in communication with the well; and an access hub; wherein the access hub comprises a tree cap having a tree cap connector connected to production bore of the subsea Christmas tree and an upper connector configured to be connected to an intervention apparatus; 
     and wherein a conduit between the tree cap connector and the upper connector provides an intervention path from an intervention apparatus to a production bore of the subsea Christmas tree. 
     Embodiments of the seventh aspect of the invention may include one or more features of the first to sixth aspects of the invention or their embodiments, or vice versa. 
     According to an eighth aspect of the invention there is provided an access hub for a subsea Christmas tree, the access hub comprising: 
     a mandrel cap comprising a mandrel cap connector configured to be connected to an annulus bore of the subsea Christmas tree and an upper connector for connecting the mandrel cap to an intervention apparatus; 
     wherein, in use, a conduit between the mandrel cap connector and the upper connector provides an intervention path from an intervention apparatus to the annulus bore of the subsea Christmas tree. 
     Embodiments of the eighth aspect of the invention may include one or more features of the first to seventh aspects of the invention or their embodiments, or vice versa. 
     According to a ninth aspect of the invention, there is provided a subsea oil and gas production system comprising: 
     a subsea well; a subsea Christmas tree in communication with the well; and an access hub; wherein the access hub comprises a mandrel cap having a mandrel cap connector connected to an annulus bore of the subsea Christmas tree, and an upper connector configured to be connected to an intervention apparatus; 
     and wherein a conduit between the mandrel cap connector and the upper connector provides an intervention path from an intervention apparatus to an annulus bore of the subsea Christmas tree. 
     Preferably, the tree comprises one or more pressure barriers and may comprise a dust and/or debris cap. The mandrel cap is preferably deployed for a particular subsea intervention operation or series of operations and recovered to surface, although it may alternative be pre-installed on the Christmas tree and left in situ at a subsea location for later performance of a subsea intervention operation. 
     Embodiments of the ninth aspect of the invention may include one or more features of the first to eighth aspects of the invention or their embodiments, or vice versa. 
     According to a tenth aspect of the invention there is provided a combined fluid injection and sampling apparatus for a subsea oil and gas production flow system, the apparatus comprising: 
     a body defining a conduit therethrough; 
     a first connector for connecting the body to the flow system; 
     a second connector for connecting the body to a fluid injection apparatus; 
     wherein, in use, the conduit provides an injection path from the intervention apparatus to the flow system; 
     and wherein the apparatus further comprises a sampling subsystem for collecting a fluid sample from the flow system. 
     Preferably the sampling chamber is in fluid communication with the flow system via the first connector. 
     The apparatus preferably comprises a third connector for connecting the apparatus to a downstream flowline such as a jumper flowline. Therefore the apparatus may be disposed between a flowline connector and a jumper flowline, and may provide a flow path from the flow system to the jumper flowline, and may also establish an access point to the flow system, via the conduit and the first connector. 
     The second connector may comprise a hose connector. The apparatus may comprise a hose connection valve, which may function to shut off and/or regulate flow from a connected hose through the apparatus. The hose connection valve may comprise a choke, which may be adjusted by an ROV (for example to regulate and/or shut off injection flow). 
     Preferably the apparatus comprises an isolation valve between the first connector and the second connector. The isolation valve preferably has a failsafe close condition, and may comprise a ball valve or a gate valve. The apparatus may comprise a plurality of isolation valves. 
     The sampling subsystem may comprise an end effector, which may be configured to divert flow to a sampling chamber of the sampling subsystem of the apparatus, for example by creating a hydrodynamic pressure. 
     An inlet to the sampling chamber may be fluidly connected to the first connector. An outlet to the sampling chamber may provide a fluid path for circulation of fluid through the chamber and/or exit to a flowline. 
     Preferably, the sampling subsystem comprises a sampling port, and may further comprise one or more sampling needle valves. The sampling subsystem may be configured for use with a sampling hot stab. 
     The sampling subsystem may be in fluid communication with the flow system via a flow path extending between the first and third connectors. Alternatively or in addition the sampling subsystem may be in fluid communication with the flow system via a flow path extending between the first and second connectors. 
     Alternatively or in addition the sampling subsystem may be in fluid communication with the flow system via at least a portion of an injection bore. 
     Embodiments of the tenth aspect of the invention may include one or more features of the first to ninth aspects of the invention or their embodiments, or vice versa. In particular, apparatus or systems of the first to ninth aspects of the invention may be configured with a sampling subsystem as described (to be used with in a sampling operation) and/or an injection flow path (for use in an injection operation), and the apparatus or systems of the first to ninth aspects of the invention may be configured for just one of sampling or injection. 
     According to an eleventh aspect of the invention there is provided a subsea oil and gas production system comprising: 
     a subsea well; a subsea Christmas tree in communication with the well; and a combined fluid injection and sampling unit; 
     wherein the a combined fluid injection and sampling unit comprises a first connector connected to the flow system and a second connector for connecting the body to an intervention apparatus; 
     wherein, in use, the conduit provides an injection path from an injection apparatus to the flow system; 
     and wherein the apparatus further comprises a sampling subsystem for collecting a fluid sample from the flow system. 
     The system may further comprise an injection hose, which may be connected to the combined fluid injection and sampling unit. The hose may comprise an upper hose section and a subsea hose section. The upper and subsea hose sections may be joined by a weak link connector. 
     The weak link connector may comprise a first condition, in which the connection between the upper hose and the subsea hose is locked, and a second (operable) condition, in which the upper hose is releasable from the subsea hose. 
     Embodiments of the eleventh aspect of the invention may include one or more features of the first to tenth aspects of the invention or their embodiments, or vice versa. 
     According to a twelfth aspect of the invention there is provided a method of performing a subsea intervention operation, the method comprising: 
     providing a subsea well and a subsea flow system in communication with the well; 
     providing a combined fluid injection and sampling apparatus on the subsea flow system, the combined fluid injection and sampling apparatus comprising a first connector for connecting the apparatus to the flow system and a second connector for connecting the apparatus to a fluid injection apparatus; 
     connecting an injection hose to the second connector; 
     accessing the subsea flow system via an injection bore between the first and second connectors. 
     Preferably the combined fluid injection and sampling apparatus is pre-installed on the subsea flow system and left in situ at a subsea location for later performance of a subsea intervention operation. The injection hose may then be connected to the pre-installed unit and the method performed. 
     Preferably the method is a method of performing a fluid intervention operation. The method may comprise fluid sampling, fluid diversion, fluid recovery, fluid injection, fluid circulation, fluid measurement and/or fluid metering. 
     The method may be a method of performing a well scale squeeze operation. 
     The method may comprise performing a well fluid sampling operation. A preferred embodiment of the invention comprises: (a) performing a fluid injection operation; and (b) performing a well fluid sampling operation. Preferably the fluid injection operation and the well fluid sampling operation are both carried out by accessing the subsea flow system via the intervention path of the access hub. 
     Embodiments of the twelfth aspect of the invention may include one or more features of the first to eleventh aspects of the invention or their embodiments, or vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: 
         FIG. 1  is a part-sectional view of a subsea production system according to a first embodiment of the invention; 
         FIG. 2  is an enlarged sectional view of an alternative hub of the embodiment of  FIG. 1 ; 
         FIG. 3  is an enlarged sectional view of a jumper hub assembly of the embodiment of  FIG. 1 ; 
         FIG. 4  is a part-sectional view of a subsea production system according to an alternative embodiment of the invention; 
         FIG. 5  is an enlarged sectional view of an alternative jumper hub, as used in the embodiment of  FIG. 4 ; 
         FIG. 6  is a sectional view of a subsea production tree system according to an alternative embodiment of the invention, including an alternative jumper hub assembly; 
         FIG. 7  is a sectional view of an alternative jumper hub spool piece that may be used with the embodiment of  FIG. 6 ; 
         FIG. 8  is a sectional view of a subsea production tree system incorporating a modified tree cap according to an embodiment of the invention; 
         FIG. 9  is an enlarged sectional view of a tree cap injection hub according to an alternative embodiment of the invention, and which may be used with the embodiments of  FIG. 8 ; 
         FIG. 10  is a part-sectional view of a horizontal style subsea production tree system according to an embodiment of the invention; 
         FIG. 11  is an enlarged sectional view of a tree cap injection hub used with a system of  FIG. 10 ; 
         FIGS. 12A and 12B  show schematically a subsea system used in successive stages of a well squeeze operation; 
         FIGS. 13A and 13B  show schematically the subsea system used in successive stages of a production fluid sample operation; and 
         FIG. 14  is a sectional view of a combined injection and sampling hub used in the systems of  FIGS. 12 and 13 , when coupled to an injection hose connection. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring firstly to  FIG. 1 , there is shown a production system generally depicted at  10 , incorporating a subsea manifold in the form of a conventional vertical dual bore Christmas tree  11  located on a wellhead (not shown). The system  10  is shown in production mode, in a part-sectional view to show some external components from a side elevation and some parts of the system in longitudinal section. The tree  11  comprises a production bore  12  in communication with production tubing (not shown) and an annulus bore  16  in communication with the annulus between the casing and the production tubing. The upper part of the system  10  is closed by a conventional tree cap  17 . 
     The production bore  12  comprises hydraulically controlled valves which include a production master valve  18  and a production swab valve  20  (as is typical for a vertical subsea tree). The production bore  12  also comprises a branch  22  which in includes production choke valve  24 , and which may be closed from the bore  12  via production wing valve  26 . The production branch  22  also includes an outlet conduit  28  leading to a flowline connector  30 , which in this case is an ROV clamp, but may be any industry standard design including but not limited to ROV clamps, collet connectors, or bolted flanges. In this example the flowline connector  30  is horizontally oriented, and would conventionally be used for connection of a horizontally or vertically deployed jumper flowline. 
     On the annulus side, the annulus bore  16  comprises an annulus master valve  32  located below an annulus branch  34 , which includes an annulus wing valve  36  which isolates the annulus branch  34  and annulus choke valve  38  from the bore  16 . An annulus outlet conduit  40  leads to a flowline connector  42  (which as above may be any industry standard design). 
     The production system  10  is provided with a flow jumper hub assembly, generally shown at  50 , and process equipment  60 . An enlarged sectional view of the flow jumper hub assembly  50  is provided at  FIG. 2 . The assembly  50  includes a first jumper hub  51  connected into the flowline connector  30  of the production branch  22 , and a second jumper hub  52  connected to the first jumper hub  51 . The first jumper hub  51  defines a main flowline bore  53  and includes a valve  54  located after opening  56 . The second hub  52  and continues the main flowline bore  53  for connection into the primary production flowline (not shown) and includes opening  58 . The openings  56  and  58  provide access points to the production system for a range of fluid intervention operations. These might include (but are not limited to) fluid sampling, fluid diversion, fluid recovery, fluid injection, fluid circulation, fluid measurement and/or fluid metering. In this case, when the valve  54  is closed, the opening  56  of the first hub  51  provides an outlet for fluid to flow from the production flowline to the processing equipment  60 , and the opening  58  of the second hub  52  provides an inlet for re-entry of the processed fluid from the process equipment  60  to the production flowline. 
     By providing intervention access points in the flowline jumper, a number of advantages are realised compared with the prior art proposals which rely on access via choke bodies on the tree. Firstly, the production choke valve  24  remains in its originally intended position and therefore may be accessed and controlled using conventional techniques. Secondly, the flowline jumper hub assembly  50  may be engineered to support dynamic and/or static loads imparted by a wide range of fluid intervention equipment and processes, and is not subject to the inherent design limitations of the choke body of the tree. Thirdly, while there are spatial limitations around the choke body of the tree, the flowline jumper hub assembly may be located in a position which allows larger items and/or different configurations of process equipment to be positioned, and may also provide improved access of ROVs and/or divers to the process equipment or other components of the tree (such as the choke). In addition, the described configuration has application to a wide-range of production manifolds, including those which do not have integrated choke bodies (as is the case for example with some designs of subsea tree). 
     The system  10   FIG. 1  also shows an alternative hub, depicted generally at  70 , which may be used as an alternative or in addition to the flowline jumper hub assembly  50  in alternative embodiments of the invention. An enlarged sectional view of the hub  70  is shown in  FIG. 3 . The hub  70  includes an inlet  72  for connection to a flow-block or pipe of a production manifold, and an outlet  74  (shown capped in  FIGS. 1 and 3 ) configured to be connected to process equipment (such as for a fluid intervention operation as described above). In this embodiment, the hub  70  is configured to be mounted on the choke valve body (without removal of the choke valve itself). This means that is able to function as an access point for fluid intervention without interfering with the position and/or functionality of the production choke. In this embodiment, the inlet  72  and the outlet  74  are perpendicularly oriented to provide vertical access to a horizontal connection point in the manifold (or vice versa). Other configurations may of course be used in alternative embodiments of the invention. 
     The hub  70  may be used in combination with another access hub described herein, for example the hub assembly  50 . In this latter case, the hub  70  may provide an inlet to process equipment for a fluid intervention operation and one of the openings of the hub  50  (conveniently the opening  58  which is downstream of the valve  54 ) may provide an inlet for re-entry of the processed fluid from the process equipment to the production flowline. 
     Although the hub assembly  50  and the hub  70  are described above with the context of a production system, and are shown to provide access points for the production wing of the tree, it will be appreciated that the hubs  50  and  70  may also be used in other modes and in particular can be connected to the annulus wing, for example to provide similar functionality in an injection process. The same applies to other embodiments of the invention unless the context specifically requires otherwise. Although the hub  70  is shown connected to an external opening of a choke body, other locations on the flow system may be used to provide access to the flow system via the hub, For example, the hub may be configured to be connected to any flange point in the flow system, the removal a blind flange providing a flange connection point for the hub  70 . In particular the hub may be connected via any external opening may be downstream of a wing valve of the Christmas tree. 
     Referring now to  FIG. 4 , there is shown a production system according to an alternative embodiment of the invention, generally depicted at  100 , incorporating a subsea manifold  11  which is the same as the conventional vertical dual bore Christmas tree of  FIG. 1 . Like components are indicated by like reference numerals. The system  100  is shown in production mode, in a part-sectional view to show some external components from a side elevation and some parts of the system in longitudinal-section. 
     The system  100  differs from the system  10  in that it is provided with an alternative jumper hub  150 , which comprises a single hub opening  151  on a main flowline bore  153 . An enlarged view of the jumper hub  150  is shown in  FIG. 5 . The jumper hub  150  is connected to the flowline connector  30  of the production branch outlet conduit  28 , and at its opposing end has a standard flowline connector  154  for coupling to a conventional jumper  156 . The embodiment of  FIGS. 4 and 5  provide similar benefits to the embodiment of  FIGS. 1 and 2 , albeit with a single access point to the system  100 . The hub  150  is relatively compact and robust and offers the additional advantage that it may be connected to the tree at surface (prior to its deployment subsea) more readily than larger hub assemblies. 
     The hub  150  may be used in combination with another access hub described herein, for example the hub assembly  50  or the hub  70 . In the latter case, the hub  70  may provide an inlet to process equipment for a fluid intervention operation and the hub  150  may provide an inlet for re-entry of the processed fluid from the process equipment to the production flowline. 
     Referring now to  FIG. 6 , there is shown a production system according to a further alternative embodiment of the invention, generally depicted at  200 , incorporating a subsea manifold in the form of a tree  211  which is similar to the conventional vertical dual bore Christmas tree  11  of  FIG. 1 . Like components are indicated by like reference numerals incremented by 200. The system  200  is also shown in production mode, in a part-sectional view to show some external components from a side elevation and some parts of the system in longitudinal-section. 
     The system  200  differs from the systems  10  and  100  in the nature of the jumper hub assembly  250  and its connection to the tree  211 . In this case the hub assembly  250  comprises a first hub  251  connected to a vertically-oriented flowline connector  230  on the production outlet conduit  228 , and a second jumper hub  252  connected to the first jumper hub  251 . Each hub  251 ,  252  comprises an opening ( 256 ,  258  respectively) for facilitating access to process equipment  60 , and functions in a similar manner to the hub assembly  50  of system  10 . In this case, the hub  251  does not include a valve, and instead directs all of the fluid to the outlet and into the process equipment  60 . However, in this embodiment the first jumper hub  251  comprises a vertically-oriented spool piece  260  with a perpendicular bend  262  into a horizontal section  264  on which the openings  256 ,  258  are located. The second hub  252  is connected to a vertically oriented ‘U’ spool jumper flowline  266 . This embodiment provides a convenient horizontal section for access to the production flow for fluid intervention in a vertical ‘U’ spool configuration. 
     Referring now to  FIG. 7 , there is shown a detail of an alternative configuration  300  according to an embodiment of the invention, which includes a simple jumper hub  350  analogous to the hub  150  used with the production system  100 . Hub  350  comprises a single hub opening  351  on a main flowline bore  353 , and is connected to the flowline connector  230  of the production branch outlet conduit of the tree  211 . At its opposing end has a standard flowline connector  354  for coupling to a vertically oriented ‘U’ spool jumper  356 . The embodiment of  FIG. 7  provides similar benefits to the embodiment of  FIGS. 4 and 5 , albeit with a single access point to the system. The hub  350  is relatively compact and robust compared to the hub assembly  250  and facilitates connection to the tree at surface (prior to its deployment subsea). 
     The hub  350  may be used in combination with another access hub described herein, for example the hub assembly  50  or the hub  70 . In the latter case, the hub  70  may provide an inlet to process equipment for a fluid intervention operation and the hub  350  may provide an inlet for re-entry of the processed fluid from the process equipment to the production flowline. Alternatively or in addition, the configuration  300  may be modified to include a double hub assembly similar to the hub  50  in place of the hub  350 , which may or may not include a valve in the main flowline bore. 
     The above-described embodiments provide a number of configurations for accessing a flow system in an oil and gas production system, which are flexible and suitable for use with and/or retrofitting to industry standard or proprietary oil and gas production manifolds. The invention extends to alternative configurations which provide access points through modified connections to the cap or mandrel of the tree, as described below. 
       FIG. 8  shows a production system according to a further alternative embodiment of the invention, generally depicted at  400 , incorporating a subsea manifold  11  which is a conventional vertical dual bore Christmas tree as shown in  FIG. 1 . Like components are indicated by like reference numerals incremented by 400. The system  400  is also shown in a part-sectional view to show some external components from a side elevation and some parts of the system in longitudinal-section. 
     In place of the conventional tree cap  17  used in the embodiments of  FIGS. 1, 4, and 6 , the system  400  comprises a tree cap hub (or modified tree cap)  417 . The tree cap hub includes an axially (vertically) oriented pressure test line  418  which is in communication with the production bore  12  of the tree via a production seal sub  420 . The pressure test line  418  extends axially through the tree cap to an opening  422  at the top of the cap. A debris cap  424  is placed over the tree cap  417  and includes a blind cap  426  to seal the opening  422 . The blind cap  426  is removably fixed to the debris cap  424 , in this case by an ROV style clamp. A dog leg  428  in the pressure test line aligns the line concentrically with the cap (from the offset position of the production bore). The pressure test line  418  is an axial continuation of the production pressure test line  430  from the position at which it extends radially through the tree cap, right through the cap and up to the top of the cap. However, the inner diameter of the pressure test line is significantly greater compared with the bore size of the conventional pressure test line  430  to facilitate fluid intervention through the cap  417 . Typical dimensions would be of the order of around 40 mm to 80 mm inner diameter, compared with around 6 mm inner diameter for a typical pressure test line (which is therefore not suitable for fluid intervention). 
     Also shown in  FIG. 8 , and in an enlarged view in  FIG. 9 , is a tree cap hub connector  450  for use with the modified tree cap  417  in the system  400 . The tree cap hub connector  450  comprises a coupling  452  which allows it to be placed over the tree cap  417  after removal of the debris cap  424  and blind cap  426 . The tree cap hub connector  450  has a bore  454  which is in fluid communication with the modified pressure test line  418 . A valve  456  in the bore  454  allows controllable connection to process equipment, which may for example be a fluid injection system. In such a configuration, the tree cap hub  417  functions as an injection hub and provides a convenient access point for injection of fluids directly into the production bore of the tree, via the pressure test line  418 , through the tree cap  417 , and into the production bore  12  itself. 
     Significantly, the above-described tree cap hub  417  provides a convenient and flexible way of carrying out fluid interventions which does not rely on the removal of or interference with choke valves. In addition, the tree cap itself is typically able to withstand static and dynamic loading far in excess of the choke bodies, which facilitates mounting of large and massive process equipment associated with the fluid intervention operations onto the tree. 
     Referring now to  FIG. 10 , there is shown generally at  500  a subsea production system consisting of a horizontal-style Christmas tree  511  on a wellhead (not shown). The system  500  is shown in tree mandrel fluid injection mode, in a part-sectional view to show some external components from a side elevation and some parts of the system in longitudinal-section. The tree  511  comprises a production bore  512  in communication with production tubing (not shown). A production wing  514  incorporates the production master valve  518  and a production wing valve  520  oriented horizontally in the production wing  514 , and a production choke valve  524  controls flow to a production outlet and vertically-oriented flowline connector  530 . 
     An annulus bore  516  is in fluid communication with the production wing via a cross-over loop  519 . The upper part of the tree  511  is closed by upper and lower plugs  523 ,  525  respectively. 
     Also shown in  FIG. 10 , and in an enlarged view in  FIG. 11 , is a tree mandrel hub  550  for use with the system  500 . The tree mandrel hub  550  comprises a mandrel connector hub  552  which allows it to be placed over the tree mandrel  517 . The tree mandrel hub  550  has a bore  554  which is in fluid communication with annulus bore  516 , and a valve  556  in the bore  554  allows controllable connection to process equipment such as a fluid injection system. In such a configuration, the tree mandrel hub  550  functions as an injection hub and provides a convenient access point for injection of fluids into the production bore of the tree, via the annulus bore  516 , through the crossover loop  519 , into the production wing  514 , and into the production bore  512  itself. 
     The tree mandrel injection hub  550  provides another convenient means of performing fluid intervention, this time via the annulus of a horizontal style tree. This embodiment offers similar advantages to the embodiment of  FIGS. 8 and 9  including minimal interference with the choke valves, flexibility of operation, and use of larger scale process equipment and/or application to wide range of subsea manifolds. It will be appreciated that the embodiments of  FIGS. 8 to 11  may be used in production mode in addition to the fluid injection modes described above. 
     It will be appreciated that the present invention provides a hub for access to a subsea flow system that facilitates a wide range of different subsea operations. One example application to a combined injection and sampling hub will be described with reference to  FIGS. 12 to 14 . 
       FIGS. 12A and 12B  are schematic representations of a system, generally shown at  600 , shown in different stages of a subsea injection operation in a well squeeze application. The system  600  comprises a subsea manifold  611 , which is a conventional vertical dual bore Christmas tree, similar to that shown in  FIG. 1  and  FIG. 4 . The subsea tree configuration utilises a hub  650  to provide access to the flow system, and is similar to the system shown in  FIG. 4 , with internal tree components omitted for simplicity. The flowline connector  630  of the production branch outlet conduit (not shown) is connected to the hub  650  which provides a single access point to the system. At its opposing end, the hub  650  comprises a standard flowline connector  654  for coupling to a conventional jumper  656 . In  FIG. 12A , the hub  650  is shown installed with a pressure cap  668 . Optionally a debris and/or insulation cap (not shown) may also be provided on the pressure cap  668 . 
     The system  600  also comprises an upper injection hose  670 , deployed from a surface vessel (not shown). The upper injection hose  670  is coupled to a subsea injection hose  672  via a weak link umbilical coupling  680 , which functions to protect the subsea equipment, including the subsea injection hose  672  and the equipment to which it is coupled from movement of the vessel or retrieval of the hose. The subsea injection hose  672  is terminated by a hose connection termination  674  which is configured to be coupled to the hub  650 . The hub  650  is configured as a combined sampling and injection hub, and is shown in more detail in  FIG. 14  (when connected to the hose connection  674  in the mode shown in  FIG. 12B ). 
     As shown most clearly in  FIG. 14 , the hose connection termination  674  incorporates a hose connection valve  675 , which functions to shut off and regulate injection flow. The hose connection valve  675  in this example is a manual choke valve, which is adjustable via an ROV to regulate injection flow from the hose  672 , through the hose connection  674  and into the hub  650 . The hose connection  674  is connected to the hub via an ROV style clamp  677  to a hose connection coupling  688 . 
     The hub  650  comprises an injection bore  682  which extends through the hub body  684  between an opening  686  from the main production bore  640  and the hose connection coupling  688 . 
     Disposed between the opening  686  and the hose connection coupling  688  is an isolation valve  690  which functions to isolate the flow system from injection flow. In this example, a single isolation valve is provided, although alternative embodiments may include multiple isolation valves in series. The isolation valve  690  is a ball valve, although other valve types (including but not limited to gate valves) may be used in alternative embodiments of the invention. The valve  690  is designed to have a fail-safe closed condition (in embodiments with multiple valves at least one should have a fail-safe closed condition). 
     The hub  650  is also provided with a sampling chamber  700 . The sampling chamber comprises an inlet  702  fluidly connected to the injection bore  682 , and an outlet  704  which is in fluid communication with the main production bore  640  downstream of the opening  686 . The sampling chamber  700  is provided with an end effector  706 , which may be pushed down into the flow in the production bore  640  to create a hydrodynamic pressure which diverts flow into the injection bore  682  and into the sampling chamber  700  via the inlet  702 . Fluid circulates back into the main production bore via the outlet  704 . 
     In an alternative configuration the inlet  702  may be fluidly connected directly to the production bore  640 , and the end effector  706  may cause the flow to be diverted into the chamber  700  directly from the bore  640  via the inlet. 
     The sampling chamber  700  also comprises a sampling port  708 , which extends via a stem  710  into the volume defined by the sampling chamber. Access to the sampling port  708  is controlled by one or more sampling needle valves  712 . The system is configured for use with a sampling hot stab  714  and receptacle which is operated by an ROV to transfer fluid from the sampling chamber into a production fluid sample bottle (as will be described below with reference to  FIGS. 13A and 13B ). 
     The operation of the system  600  in an application to a well squeeze operation will now be described, with reference to  FIGS. 12A and 12B . The operation is conveniently performed using two independently operated ROV spreads, although it is also possible to perform the operation with a single ROV. In the preparatory steps a first ROV (not shown) inspects the hub  650  with the pressure cap  668  in place, in the condition as shown in  FIG. 12A . Any debris or insulation caps (not shown) are detached from the hub  650  and recovered to surface by the ROV. The ROV is then used to inspect the system for damage or leaks and to check that the sealing hot stabs are in position. The ROV is also used to check that the tree and/or jumper isolation valves are closed. Pressure tests are performed on the system via the sealing hot stab (optionally a full pressure test is performed), and the cavity is vented. The pressure cap  668  is then removed to the ROV tool basket, and can be recovered to surface for inspection and servicing if required. 
     The injection hose assembly  670 / 672  is prepared by setting the weak link coupling  680  to a locked position and by adjusting any trim floats used to control its buoyancy. The hose connection valve  675  is shut off and the hose is pressure tested before setting the hose pressure to the required deployment value. A second ROV  685  is deployed below the vessel (not shown) and the hose is deployed overboard to the ROV. The ROV then flies the hose connection  674  to the hub  650 , and the connection  674  is clamped onto the hub and pressure tested above the isolation valve  690  via an ROV hot stab. The weak link  680  is set to its unlocked position to allow it to release the hose  670  from the subsea hose  672  and the hub  650  in the event of movement of the vessel from its location or retrieval of the hose. 
     The tree isolation valve is opened, and the injection hose  672  is pressurised to the desired injection pressure. The hose connection valve  675  is opened to the desired setting, and the isolation valve is opened. Finally the production wing isolation valve is opened to allow injection flow from the hose  672  to the production bore to commence and the squeeze operation to be performed. On completion, the sequence is reversed to remove the hose connection  674  and replace the pressure cap  668  and any debris/insulation caps on the hub  650 . 
     It is a feature of this aspect and embodiment of the invention that the hub  650  is a combined injection and sampling hub; i.e. the hub can be used in an injection mode (for example a well squeeze operation as described above) and in a sampling mode as described below with reference to  FIGS. 13A and 13B . 
     The sampling operation may conveniently be performed using two independently operated ROV spreads, although it is also possible to perform this operation with a single ROV. In the preparatory steps, a first ROV (not shown) inspects the hub  650  with its pressure cap  668  in place (as shown in  FIG. 13A ). Any debris or insulation cap fitted to the hub  650  is detached and recovered to surface by a sampling Launch and Recovery System (LARS)  720 . The ROV is used to inspect the system for damage or leaks, and to check that the sealing hot stabs are in position. 
     The sampling LARS  720  subsequently used to deploy a sampling carousel  730  from the vessel (not shown) to depth and a second ROV  685  flies the sampling carousel  730  to the hub location. The pressure cap  668  is configured as a mount for the sampling carousel  730 . The sampling carousel is located on the pressure cap locator, and the ROV  685  indexes the carousel to access the first sampling bottle  732 . The hot stab (not shown) of the sampling bottle is connected to the fluid sampling port  708  to allow the sampling chamber  700  to be evacuated to the sampling bottle  732 . The procedure can be repeated for multiple bottles as desired or until the bottles are used. 
     On completion, the sample bottle carousel  730  is detached from the pressure cap  668  and the LARS  720  winch is used to recover the sample bottle carousel and the samples to surface. The debris/insulation cap is replaced on the pressure cap  668 , and the hub is left in the condition shown in  FIG. 13A . 
     The invention provides an apparatus and system for accessing a flow system (such as a subsea tree) in a subsea oil and gas production system, and method of use. The apparatus comprises a body defining a conduit therethrough and a first connector for connecting the body to the flow system. A second connector is configured for connecting the body to an intervention apparatus, such as an injection or sampling equipment. In use, the conduit provides an intervention path from the intervention apparatus to the flow system. Aspects of the invention relate to combined injection and sampling units, and have particular application to well scale squeeze operations. 
     Embodiments of the invention provide a range of hubs and/or hub assemblies which facilitate convenient intervention operations. These include fluid introduction for well scale squeeze operations, well kill, hydrate remediation, and/or hydrate/debris blockage removal; fluid removal for well fluid sampling and/or well fluid redirection; and/or the addition of instrumentation for monitoring pressure, temperature, flow rate, fluid composition, erosion and/or corrosion. Aspects of the invention facilitate injection and sampling through a combined unit which provides an injection access point and a sampling access point. Other applications are also within the scope of the invention. 
     It will be appreciated that the invention facilitates access to the flow system in a wide range of locations. These include locations at or on the tree, including on a tree or mandrel cap, adjacent the choke body, or immediately adjacent the tree between a flowline connector or a jumper. Alternatively the apparatus of the invention may be used in locations disposed further away from the tree. These include (but are not limited to) downstream of a jumper flowline or a section of a jumper flowline; a subsea collection manifold system; a subsea Pipe Line End Manifold (PLEM); a subsea Pipe Line End Termination (PLET); and/or a subsea Flow Line End Termination (FLET). 
     Various modifications may be made within the scope of the invention as herein intended, and embodiments of the invention may include combinations of features other than those expressly described herein.