Christmas tree

Information

  • Patent Grant
  • 6227301
  • Patent Number
    6,227,301
  • Date Filed
    Monday, January 11, 1999
    25 years ago
  • Date Issued
    Tuesday, May 8, 2001
    23 years ago
Abstract
A Christmas tree (16) is based on a dual bore sub-sea test tree. The Christmas tree consists of a Christmas tree housing (56), which connects to a wellhead (44), a Christmas tree valve block assembly (62) disposed in the housing (56) and a tree cap (84) which connects to the housing (56) and valve block assembly (62). In a preferred embodiment the valve block assembly (62) has a main production bore (70) with two valves (72,74) in series and two auxiliary bores (76,96). One auxiliary bore (96) has a valve (98) for facilitating control of the annulus bore (96) whereas the other annulus bore (76) has no valve and provides a pathway for an electrical submersible cable (66) to a pump. The valves (72,74,98) are actuatable via control from an umbilical (94) and provide the facility to seal the production and annulus access bores to meet statutory requirements. A tubing hanger is not required.
Description




The present invention relates to a xmas tree structure for use in extended well tests. In particular, the invention relates to a simplified horizontal xmas tree structure for use in such tests and to a method of installing such a tree for use in such extended well tests.




Extended well tests (EWTs) are procedures which can last up to 180 days and are carried out in order to assess the viability of a producing reservoir and to obtain accurate reservoir data over a prolonged period. Extended well tests are common for on-shore locations requiring little more than a conventional well test package. Off-shore packages are somewhat different due to tighter regulatory, product and effluent specifications. Due to the extended flow periods, crude oil is normally recovered for commercial sale from the extended well test. Off-shore systems are highly sensitive to well performance because the cost of a rig and export system has to be accounted for. It is of considerable importance to be able to minimise the cost of conducting extended well tests and the apparatus used in the tests without comprising the accuracy of reservoir data or compromising safety.




Extended well tests are typically conducted using a traditional sub-sea test tree and BOP stack. However, if additional wells are also to be tested, or if an injectivity test is to be conducted, it will be necessary to deploy a sub-sea xmas tree to provide well pressure control. For applications in which well testing involves testing more than one well, the term “extended appraisal test” (EAT) is used in place of the term extended well test (EWT). Traditional xmas tree are relatively expensive and require additional accessories and tools such as tubing hangers and tubing hanger running tools and a workover system in order to conduct the extended well test further adding to the rig time and overall cost of conducting the well test.




An object of the present invention is to provide a pressure control system embodied in a simplified structure and a method of its deployment which obviates or mitigates at least one of the disadvantages associated with existing xmas trees.




This is achieved by providing a simplified xmas tree based on a dual bore sub-sea test tree. A separate tubing hanger is not required and the main bore of the sub-sea test tree is used as the production bore. In a preferred embodiment, an axial bore, which includes an isolation valve, is provided for communication with the well annulus and an additional axial bore is occupied by an electrical power cable for supplying an electrical submersible pump (ESP).




According to a first aspect of the present invention there is provided a xmas tree for use in a variety of well applications, said xmas tree comprising:




a generally cylindrical xmas tree housing defining a generally cylindrical bore, a separate xmas tree valve disposed within the cylindrical bore of said xmas tree housing and engaged with the xmas tree housing, and a xmas tree cap for engaging with said valve block, or said xmas tree housing, the xmas tree cap being coupled to a rig via various flowline and umbilical services to facilitate control of the xmas tree in conveying fluids between surface mounted process facility and a downhole reservoir,




the xmas tree valve block having a main production bore and at least one auxiliary bore, the main production bore having at least two valves axially spaced therein, said valves being operable to seal the bore and provide well barriers, said at least one auxiliary bore providing an annulus access bore and containing a single valve operable to seal the access bore and provide a well barrier in the annulus.




Conveniently, the xmas tree valve block has a main production bore and two auxiliary bores. One auxiliary bore provides the annulus access bore and has a valve therein and the other auxiliary bore has no valve but is used for receiving a power cable for driving an electrical submersible pump.




In the absence of a requirement for an electrical submersible pump, no power cable is used and a single axial bore for the cable is provided or, if two bores are present, the additional bore is blocked and sealed. A single axial annulus access bore is provided for providing annulus control regardless whether or not there is a power cable disposed in said auxiliary bore.




It will also be appreciated that each of the bores has sealing means to seal the bores so that leakage of fluid from the bore is prevented when the tree cap is made up to the valve block and/or valve housing.




Preferably also, said valves in series within said production bore and the annulus bore are ball valves. Alternatively, said valves are flapper valves, disc valves or plug valves.




Preferably also, the housing engages with a standard wellhead connector to enable it to be attached to a sub-sea wellhead and the valve block is proportioned and dimensioned to fit in within the bore of this housing and the housing is adapted to be received by the tree cap so that connection is made between parts of the production bore, and parts of the two auxiliary bores to provide effective connection for these bores. The connections in the production and annulus bore are hollow pin and socket connections. The connections in the bores for electrical communication are of a wet mateable connection in the power and signal cables. The connections in the controls parts are also by hollow pins and sockets.




Conveniently also, locking means are provided between the xmas tree housing and the valve block assembly which are actuated when the tree cap fits on to the valve block to lock the valve block to the xmas tree housing, and to provide fine alignment between the tree cap and the housing. Conveniently, the locking means are radially acting dogs which are actuated by axial movement of a ring within the tree cap locking means. The top surface of the upper end of the valve block, which is level with the top of the housing, is provided with profiles to accommodate:




1) the sealing of the production and annulus bores,




2) the sealing of the hydraulic ports required for the control of the actuation of xmas tree and other well functions,




3) repeatable make and break of connections in the communications of electric signals between the surface and the electrical equipment located within the well,




4) repeatable make and break of connections in the communications of electrical power between the surface and electric submersible pump.




The external surface of the upper end of the valve block is provided with at least one shaped keyway to ensure correct angular alignment between the xmas tree and the tree cap to facilitate correct engagement of the various connections at the top surface of the tree cap as described above.




Conveniently also, the xmas tree housing may be coupled to a guide frame which is adapted to guide and receive the tree cap when installed so that there is effective and efficient coupling between the tree cap and the tree housing and valve block. The guide base is fitted to the wellhead system, and a protective frame is attached to the tree housing which takes the guidance from the wellhead, into the tree, and hence into the tree cap.




A permanent guide base, attached to the wellhead system, including a side guide frame with guidepost spacing of the same dimensions as the guide frame coupled to the wellhead so that when the tree cap is removed for workover mode, the tree cap can be moved to one side and parked adjacent to the wellhead.




According to another aspect of the present invention there is provided a xmas tree structure comprising:




a xmas tree housing coupled to a sub-sea wellhead;




a xmas tree valve block located in said xmas tree housing, said xmas tree valve block having a production bore with at least two valves disposed in series and at least one auxiliary bore for facilitating annulus access control, said at least one auxiliary bore having a valve therein, a xmas tree cap coupled to the xmas tree valve block and to said xmas tree housing, locking means disposed in said xmas tree to fasten the xmas tree housing, xmas tree valve block and said xmas tree cap together, said respective xmas tree valves being remotely operable to be selectively moved between open and closed position to control flow or liquid through said xmas tree structure.




Conveniently, there are two auxiliary bores; one annulus access bore and a further auxiliary bore with at least one valve therein and a further auxiliary bore for receiving a power cable for supplying power to a downhole electrical submersible pump (ESP).




According to a further aspect of the present invention, there is provided a method of installing the xmas tree on a wellhead for use in a variety of well tests, the tree housing having a blow-out preventer means initially coupled thereto in place of a tree cap, said method comprising the steps of:




a) providing a xmas tree housing coupled to the wellhead, the xmas tree housing having a top part adapted to be coupled to the blow-out preventer connector,




b) running a xmas tree valve assembly through said BOP stack for engaging with the xmas tree housing and being operable for providing a well barrier to the flow of well fluid,




c) closing the well barrier to provide well isolation once the xmas tree valve assembly is located in said xmas tree housing,




d) removing the blow-out preventer stack from the xmas tree housing,




e) running in a xmas tree cap and securing the xmas tree cap to the xmas tree housing and xmas tree valve assembly to provide coupling from the production and annulus bores to the surface and from auxiliary ports and bore to the surface, the arrangement being such that the valves in the production and annulus bores can be controlled to provide control of well fluid and xmas tree functionality.




Preferably also, the method includes the step of using the xmas tree in a workover mode, said method including the additional steps of removing the xmas tree cap and parking the xmas tree cap on a further guide frame adjacent to the wellhead and xmas tree housing, and coupling a blow-out preventer stack on top of said xmas tree housing with said xmas tree assembly contained therein.











These and other aspects of the invention will be better understood from the following description when taken in combination with the accompanying drawings in which:





FIG. 1

depicts a diagrammatic representation of a semi-submersible rig coupled to two EAT trees (extended appraisal test tree) simplified xmas trees in accordance with an embodiment of the present invention shown mounted on wellheads;





FIG. 2

is a sectional elevational view through part of a simplified horizontal xmas tree housing in accordance with an embodiment of the present invention installed on a wellhead with a BOP stack shown coupled to the xmas tree;





FIG. 3

is a view similar to

FIG. 2

but depicts an insert tree valve block being installed through the BOP stack into the xmas tree housing;





FIG. 4

shows the insert tree valve block of

FIG. 3

landed within the xmas tree housing;





FIG. 5

shows a view similar to

FIG. 4

with the BOP stack removed and a simplified xmas tree in accordance with the embodiment of the present invention being completed by the installation of a xmas tree cap;





FIGS. 6



a


and


6




b


are respective perspective views of a lockdown assembly and part of a valve block respectively for locking down the valve block and providing fine angular alignment from the block to the xmas tree cap;





FIG. 6



c


is an enlarged part section through the lockdown assembly located within the xmas tree housing;





FIG. 7

is a view similar to

FIG. 5

, but drawn to a larger scale, in which the xmas tree cap is shown coupled to the xmas tree housing to define a complete simplified xmas tree ready for in production mode with the flow line controls and umbilical attached to the xmas tree cap;





FIG. 8

is a sectional view taken on the line


8





8


through the structural housing of

FIG. 7

;





FIG. 9

is a detail of part of the dual bore tree shown in FIG.


7


and taken on the lines


9





9


of

FIG. 8

to demonstrate the second auxiliary bore, providing communication with the annulus and showing the production and annulus bores with isolation valves, and





FIG. 10

is a view of the extended well test xmas tree in workover mode where the xmas tree cap has been removed and parked adjacent to the permanent guide base (PGB) and a BOP stack is connected to the structural housing.











Reference is first made to

FIG. 1

of the drawings which is a diagrammatic illustration of an extended appraisal test (EAT) tree from a semi-submersible rig


10


in which there is simultaneous production from two separate wells


12


,


14


.




Wells


12


and


14


have associated extended appraisal test (EAT) tree simplified horizontal xmas trees


16


,


18


which are located on respective wellheads


20


and


22


. A horizontal tree is one in which the completion can be pulled out of the well without the need to recover the tree. Each xmas tree


12


,


14


is coupled to the semi-submersible


10


via various lines, generally indicated by reference numeral


24


, a flexible production riser


26


, an electrical power cable


28


and a controls umbilical


30


. The umbilicals are connected to a respective rig-mounted process system


34


, control system


36


and electrical power distribution system


38


via rig-mounted EQDC (Emergency Quick Disconnect/Connect) units. Liquids which are produced during the extended well test passes through the process system, and oil is pumped to a tanker


41


via EQDC


39


add export line


40


.




The simplified xmas trees


16


,


18


on the wellheads, which will be later described in detail, are based on a dual bore sub-sea test tree and allow an extended appraisal test (EAT) to be conducted without the expense and complexity associated with traditional xmas trees.




Reference is now made to

FIG. 2

of the drawings which is an enlarged scale sectional elevation through the wellhead and the EAT xmas tree


16


which consists of a xmas tree housing installed on a wellhead with a blow-out preventer BOP attached to a structural housing. For convenience, only the simplified xmas tree


16


will be described in detail although it will be understood that xmas tree


18


has the same structure and operates in the same way. Mounted on the conductor housing


20


of the wellhead system is a four post permanent guide base (PGB)


42


which surrounds 18¾″ high pressure wellhead


44


. A guide frame


46


fitted with four funnels to capture the PGB guide posts


42




a


is coupled onto the xmas tree housing connector


48


which has dogs


50


which engage with an exterior profile


52


on the wellhead


44


to securely fasten the guide frame


46


and tree connector


48


to the wellhead


44


. The wellhead connector


48


has a connection point


55


for receiving a structural xmas tree housing


56


as shown in FIG.


2


. An internal cam profile (not shown) is provided at a pre-determined angular orientation with respect to the guide frame


42


, to engage a key on the valve block to control the angular position of the valve block in relation to the PGB


42


, in order to achieve correct landing of the tree cap. A BOP stack


60


also having a guide frame


57


, with funnels


58


which receive the posts


46




a


of frame


46


, is shown mounted on the xmas tree housing


56


. The arrangement of

FIGS. 2

,


3


and


4


depict the installation or workover mode as compared to extended well test mode.




As mentioned above, a conventional type of horizontal tree wellhead is expensive and it also requires that the tubing hanger is run prior to use of the wellhead.




This is overcome using the arrangement shown in

FIG. 3

in which an insert xmas tree valve block, generally indicated by reference numeral


62


is installed through the BOP


60


into the xmas tree housing


56


. In this case it will be understood that the insert tree valve block


62


is based on a dual bore sub-sea test tree (similar to the type disclosed in applicant's co-pending International Published Application No. PCT/GB96/01115) which carries at its lower end tubing


64


and an electrical cable


66


which is coupled to an electrical submersible pump (ESP), not shown in the interest of clarity. The installation procedure for the insert xmas tree valve block


62


will be later described but it is sufficient to note that at present, with reference to

FIG. 3

, the valve block


62


, including the tubing


64


and the cable


66


which it is carrying, passes through the BOP stack


60


and the xmas tree housing


56


.




Reference is now made to

FIG. 4

of the drawings which is similar to

FIG. 3

except that the insert tree valve block


62


has been landed on an annular landing shoulder


68


within the structural housing


56


whereby it adopts the position shown in

FIG. 4

; that is, part of the xmas tree valve block


62


extends upwardly from the xmas tree housing


56


inside the BOP stack


60


. It will be seen that the main bore


70


of the valve block


62


contains two 5″ ball valves


72


,


74


in series similar to the sub-sea test tree and, as shown in

FIGS. 8 and 9

, a smaller single valve


98


in the annulus bore


96


, and an auxiliary 2″ annulus bore


76


provides a pathway for the electrical submersible cable


66


. The ball valves


72


,


74


are qualified to a relevant xmas tree design standard, for example AP1 17D. It will be understood that the xmas tree ball valves are uni-directional sealing valves which may be used in a bi-directional application if required. Each ball valve


72


,


74


is “failsafe closed” fitted with a spring package


75


,


77


respectively to return the valve to the closed position on loss of control pressure. This is designed to give a valve closure time of approximately 30 seconds. Each ball valve has a double acting hydraulic actuator (not shown in the interest of clarity) whose axis is coincident with the axis of flow through the valve. This means that pressurised hydraulic control fluid can be applied to either the open or the closed side of the actuator. For a uni-directional sealing application, a single control line conveys pressurised control fluid to the open side of the actuator. This opens the valve against spring force, which spring force returns the valves to the closed position, on cessation of the application of pressure maintaining the valve in the open position. It will also be appreciated from

FIG. 4

that the xmas tree valve block


62


is run on a casing riser


78


and the electrical cable connection is made via a power cable


80


. An umbilical (not shown in the interest of clarity) contains a bundle of tubular conduits for the conveyance of control fluids, and for communication with the well annulus. The xmas tree housing


56


has the annular landing shoulder


68


for receiving the xmas tree valve block


62


as shown and when the valve block


62


is in the position as shown in

FIG. 4

, it is then in the correct position. Once the xmas tree valve block is installed, the ball valves


72


,


74


and


98


can be actuated to a closed position to provide well control barriers in the main bore


70


, and the annulus bore


96


also as shown in

FIG. 4

, and the BOP stack


60


can then be removed.




Reference is now made to

FIGS. 5 and 6



a, b


and


c


of the drawings;

FIG. 5

depicts installation of the xmas tree cap, generally indicated by reference numeral


84


, after the BOP stack


60


has been removed, and

FIGS. 6



a,




6




b


depict the separate parts of a lockdown assembly by which the tree cap


84


is accurately aligned orientationally to the valve block


62


and xmas tree housing


56


and

FIG. 6



c


depicts the lockdown assembly located within the xmas tree housing


56


.




The EAT tree cap connector


83


is mounted in a tree cap guide frame


85


which has four guide frame funnels


86


(only two of which are shown) so that when it is run, as shown in

FIG. 5

, the funnels


86


mate with the guide posts


46




a


of guide frame


46


, thereby providing coarse alignment between the tree cap connector


83


and the xmas tree housing


56


and tree valve block


62


. It will be seen that the tree cap connector


83


is a central perforated cylindrical block within a conventional externally attached wellhead connector, and which is of a similar structure to the wellhead connector


48


, and locks to the structural housing


56


in the same way as the wellhead connector


48


connects to the wellhead


44


. Once the valve block


62


has been landed within the housing


56


a lockdown assembly


161


, shown in

FIG. 6



a,


is installed. This has an expanding profile which engages a suitable internal profile


162


in the housing and, when set, locks the valve block


62


in the housing


56


in order to prevent its upwards movement due to well pressure acting on closed valves


72


,


74


within the valve block


62


. The lockdown assembly


161


has an outer body


161




a


and a rotatable and axially movable, via engagement of threads


166




a,b


(

FIG. 6



b


), inner ring


169


for locking the assembly to the housing


56


, as will be later described, outer body


161




a


has lower keys


163


(one of which is shown) which engage shaped keyways


165


on the external surface


167


at the upper end of the valve block, and similar upper keys


167


engage corresponding keyways


159


in the tree cap


84


, to provide fine alignment to ensure the engagement of the hollow pins and sockets, in the connections in the halves of the production and annulus bores, the power and the signal electrical connectors and the controls connections, between the tree cap


84


and the insert valve block


62


as will be described below. The assembly is run in and landed with the lower protruding keys


163


engaged with the keyway


165


in the valve block


62


. As best seen in

FIG. 6



c,


rotation of the inner body


169


expands dogs


171


to lock into a housing groove


162


. With the dogs


171


engaged, further downward travel of the inner body


169


contacts the valve block


62


to rigidise it in place within the tree housing


56


. As shown in

FIG. 5

, the tree cap connector


83


has parts which mate with the valve block including the upper part of wet mateable connectors, generally shown by numeral


88


, for making the connections in the electric signals and power to downhole equipment, generally shown by numeral


89


, and hollow, pins, generally indicated by numeral


90


, for connection with the sockets in the production, annulus and controls ports bores generally shown by numeral


92


. It will be seen that the top


90


of the tree cap


84


contains a termination


93


for the flow line and controls umbilical. It will also be seen from

FIG. 5

that the permanent guide base


42


has a side extension, generally indicated by reference numeral


99


, of the same configuration as the guide base


42


for receiving the xmas tree cap


84


from the xmas tree housing


56


in order to accommodate a workover operation which requires a BOP stack to be installed on the tree housing.




Reference is now made to

FIGS. 7 and 9

of the accompanying drawings which depicts the assembled simplified xmas tree


16


based on the xmas tree valve block


62


for providing control of reservoir fluids. The tree cap


84


is mounted on the xmas tree housing


56


with dogs


91


engaging the exterior profile


93


in the same way as the BOP stack


60


was connected. When xmas tree is assembled there is connection between the parts of the main production bore


70


, the annulus bore


96


and auxiliary bore


76


. In this arrangement, which is the production mode, it can be seen that the flow line and umbilicals, generally indicated by reference numeral


94


, are attached to the tree cap


84


. It will also be seen in

FIGS. 7 and 9

that the 5″ ball valves


72


,


74


, and 1½″ valve


98


are shown in the closed position. However, it will also be appreciated that they may be actuated via the umbilical


94


from surface to open positions to permit reservoir fluid to flow through the main production bore


70


, and to monitor pressure in the annulus bore


96


. The electrical power cable


66


, which passes through the auxiliary bore


76


, allows power to be supplied from the surface to the downhole electrical submersible pump.





FIG. 8

depicts a section through the xmas tree housing


56


on line


8





8


of FIG.


7


and it will be seen that there are three principal axial bores in the insert valve block (control axial bores have been omitted for clarity); the main 5″ production bore


70


which has the two ball valves


72


,


74


in series, the 1½″ annulus access bore


96


, and the 2″ auxiliary bore


76


, which receives the electrical power cable


66


coupled to the downhole electrical submersible pump.




Reference is also made to

FIG. 9

of the drawings which is a sectional view taken along the lines


9





9


of FIG.


8


and shows a partial sectional elevation of the tree showing through a detail


98


(shown in broken outline) of the xmas tree


16


of

FIG. 7

, depicting the production and annulus access bores


70


,


96


each with an isolation valve


74


,


98


(with the tubing omitted for clarity). It will be appreciated that with this structure, control of the annulus line


96


will be carried out in the same way as using the dual bore sub-sea test tree with the resulting advantages also being present in this arrangement.




Reference is now made to

FIG. 10

of the drawings which shows the xmas tree


16


in workover mode with the tree cap


84


removed and the flow line and umbilicals part


94


parked on the extended guide base


99


disposed adjacent to the permanent guide base


42


and with the BOP stack


60


run to again mate with the xmas tree housing


56


in the same way as shown in

FIG. 4

of the drawings.




It will be appreciated that the xmas tree valve block


62


is run on the riser


78


as if it were a sub-sea test tree and landed on the annular landing seat


68


within the xmas tree housing


56


. It will also be appreciated that because the xmas tree valve block


62


interfaces with its deployment tool


121


, and the xmas tree cap


84


having multiple axial penetrations, it must be installed in a known orientation to the permanent guide base guide posts


46


in order to ensure correct engagement with the tree cap


84


and the electrical power connector and the usual seal subs. The orientation alignment between the tree


16


and the tree cap


84


is achieved in step-like fashion with each successive step controlling more closely the alignment.




As described above, rough alignment is established between the tree guide frame funnels


58


and the post on the PGB guide frame posts


46




a,


and immediate alignment is established with the installation of the xmas tree valve insert block


62


into the housing


56


. Fine alignment is set up with the installation of the lock-down assembly (


161


) in preparation for the alignment required for the installation of the tree cap


84


.




The insert valve block


62


is provided with means of achieving correct alignment. As described above with reference to

FIGS. 6



a


and


6




b,


the keyways


165


on the external diameter of block


62


facilitates engagement with keys


167


and orientational alignment of the latch/running tool. Similarly, at the bottom end, an orientational alignment key (not shown) is fitted to the xmas tree insert valve block


62


which interacts with an internal bi-directional cam profile (not shown) within the lower end of the cylindrical xmas tree housing


56


. The angular relationship between the orientational aids or main set valve block


62


, the keys at the top and the orientation key at the bottom are controlled.




The lock-down mechanism, or assembly


161


is run in to rigidise the valve block


62


in place and also provides a fine orientational alignment. As described above, with reference to

FIGS. 6



a


to


6




c,


the underside of the lockdown mechanism


161


carries the same key profile


163


as the valve block


62


, whereas an upward facing key


167


at the top of the lock-down mechanism


161


provides a precision location for a matching keyway within the tree cap


84


.




The aforementioned structure and overview of installation and operation will give the reader an understanding of the structure and the installation procedure. However, for a better and more complete understanding regarding the running of the EAT xmas tree


16


, it will be understood that prior to and during the running of the completion, the tree components are tested for function, orientation and pressure integrity using a tree stump/shipping skip. It is anticipated that drilling is carried out conventionally with the BOP stack


60


located directly on the wellhead


44


which may be of a conventional type, for example Vetco SG-5 H-4.




A brief summary of the sequence of events regarding the running of the EAT simplified xmas trees


16


,


18


is as follows:




a) At the end of the drilling phase, the well is suspended conventionally with the appropriate plugs/suspension string. The BOP


60


is pulled and a wellhead corrosion cap (not shown) installed and the PGB guidelines are disconnected and retrieved.




b) In the event that a rig and completion equipment are available for installation of the completion immediately after drilling, it will be understood that the trip to run the corrosion cap may be eliminated.




c) The xmas tree housing


56


is then run using the running tool available from the drilling phase and is locked on the wellhead


44


using either a workover (W/O) umbilical attached to the hydraulically operated wellhead connector by using a ROV “hot stab” connection system stabbed into a suitable receptacle on the guide frame of the xmas tree spool housing


56


. The workover umbilical may then be disconnected using the ROV.




d) The BOP stack


60


is then run in the conventional way on marine riser.




e) Once the BOP stack


60


is run and is in position, as shown in

FIG. 2

, the running tool is used to run in the hole and test the VX seal, the running tool being available from the drilling phase and being fitted with a cup tester which seals the top of the production casing or the casing hanger in the wellhead.




f) Once the VX seal has been tested, the running tool and cup tester is pulled from the hole.




g) On surface the electrical submersible pump (ESP) is made up to the completion tubing and packer, the downhole chemical controls line is made up and the ESP is then run in the hole on 7″ tubing/casing with the electrical power cable and controls line being unreeled and strapped to the production tubing as necessary until the correct length of production tubing has been run in the hole.




h) The xmas tree valve block


62


will already have been made up to its running tool


121


,

FIG. 10

, on the surface and will have been stored (racked) back in the derrick. This valve block


62


, the running tool


121


and the umbilical


80


are now made up to the string


78


. The downhole electrical cable


66


cut and terminated at the termination point


130


,


131


,

FIG. 3

, to tails from the wet mate connector halves


88


,


89


at the tree cap


84


and the xmas tree valve block


62


and tested for continuity and function.




i) Assuming that the continuity and function is acceptable, the xmas tree valve block


62


is run in the hole and production tubing and landed in the xmas tree housing


56


as shown in FIG.


4


. In this position the ESP can be tested as required.




j) The xmas tree valve block running tool


121


, the running string and umbilical


80


are then retrieved from the hole.




k) The lockdown assembly


161


and running tool not shown are picked up and run in the hole on tubing or drill pipe and the valve block


62


is then rigidised within the xmas tree housing


56


by turns of right hand rotation of the lockdown assembly running tool and thereafter the lockdown assembly running tool is retrieved from the hole.




As described above, the tree cap


84


is run with the flow line, the umbilical and the electrical power cable attached to the tree cap, which all need to be pulled out from storage drums located on the rig deck or on an adjacent vessel. Once these “flexible members” have been unreeled from the respective storage drums, the free ends are delivered and connected to the EQDC system. It is necessary to have installed “keel haul” lines from the storage reel locations into the moonpool area in order to deliver the ends of the flexible members to the moonpool for attachment to the xmas tree cap


84


.




The xmas tree cap


84


is positioned on the spider beams (not shown in the interests of clarity) in the moonpool of the vessel and the respective connections of the flow line, umbilical and electrical power cable


94


are made up to the xmas tree cap


84


with the required bend restrictors, strapping and buoyancy modules being installed as required.




Thereafter, the connection is made up to the tree cap running tool


104


, the spider beams are spread and the xmas tree cap


84


picked up and run in to land it on the xmas tree housing


56


as shown in

FIG. 7

with the flexible members being strapped together at the various locations along their length as necessary.




Once in the position shown in

FIG. 7

, the tree cap connector


84


is locked in place using alternative procedures described above for running the structural housing


56


and the system is tested. The tree cap running tool


104


is then retrieved.




It will be appreciated that the tree may be retrieved using steps which are basically the reversal of the running in steps.




The workover procedures are similar to the retrieval procedures except that the tree cap


84


is not recovered to the surface provided that it is still functional. The tree cap running tool


121


is run, the tree cap connector is released and the tree cap


84


lifted off the tree


62


. A ROV is mobilised to disconnect the guidelines which are fitted with ROV releasable post tops of a proprietary manufacturer (such as Regan GL4).




As best seen in

FIG. 10

, the tree cap


84


is skidded to one side, similar to running the BOP stack


60


, and the guidelines are reconnected to a second set of posts of guide frame


92


adjacent to the normal side posts


46


, thereby forming a “parking bay” adjacent to the well attached to the existing permanent guide base


46


. The tree cap


84


is set down over the posts of the parking bay and the tree cap running tool


104


disconnected and retrieved to the surface. The ROV is remobilised to effect reconnection of the guidelines back to the well guide post tops.




This allows the BOP stack


60


to be re-run to land on the structural housing


56


of the tree, as shown in

FIG. 10

, and the completion and ESP can be pulled as a normal retrieval operation. It will also be appreciated that the tree cap can be replaced as a reversal of the foregoing steps.




Various modifications may be made to the simplified xmas tree hereinbefore described without departing from the scope of the invention. For example, the preferred embodiment describes a xmas tree with an auxiliary channel which receives a cable for use with an electrical submersible pump. However, it will be understood that the system could equally well be used in a well with natural drive in which case a conventional sub-sea test tree may be used as a valve block with the annulus line performing its normal annulus path function. It will also be understood that the ball valves may be replaced by any other type of suitable valves, such as flapper valves, which are sufficient to provide a sealing function in the production bore and the annulus bore. It will be understood that a single valve may be used in the xmas tree bore but, for safety reasons, two valves in series are preferred in the production bore, although a single valve in the annulus bore is adequate.




It will also be understood that various diameters of xmas tree housings and xmas tree valve blocks may be used. However, it will be understood that the xmas housing of 18¾″ nominal bore diameter which is the same as that of the wellhead is particularly convenient and is designed to receive a valve block assembly and machined in accordance with the diameter of a typical 5″×2″ sub-sea test tree. It will be appreciated that the dimensions of the bore and length of the tools may be varied in accordance with specific requirements and that the dimensions hereinbefore described are exemplary only.




The connection between the xmas tree cap and the xmas tree housing may be other than using a wellhead type of connector as hereinbefore described. Any other suitable connector may be used which gives an appropriate sealing function which is sufficient to comply with the safety requirements and it will be understood that the tree cap connector and structural housing connection which simulates the wellhead and wellhead connector arrangement is particularly convenient as these products already exist aid have been well tested.




In the event of a requirement to test the tree valves from above, a second control line is required to convey pressurised control fluid to the closed side of the actuator. This creates an upward force which counteracts the hydrostatic pressure acting downward on the ball from above, and maintains contact between the ball and the seat to prevent-leakage, thus facilitating the test of the valve from above, if so required.




It will also be understood that although the preferred used of the simplified xmas tree structure is an extended well test, it will nevertheless be understood that the xmas tree may be used in an early production facility or even a permanent production facility and also for water and gas injection operations where relatively quick and straightforward access to a well is required without requiring the considerable expense of a traditional xmas tree.




Advantages of the simplified xmas tree in accordance with the present invention are that the structure can be readily and quickly installed and is capable of being used in a variety of well applications, such as extended well tests, extended appraisal tests and early production facility and gas and water injection. The xmas tree uses many existing well components thereby minimising the cost and also utilises a dual bore sub-sea test tree to provide dual valve protection in the production bore, whereas the annulus bore is used to provide access into the well annulus and an auxiliary bore is used to provide a facility for receiving an electrical power cable for driving a electrical submersible pump. In the situation where a power cable is provided through, an additional bore is necessary to allow the installation of the electric power cable for an ESP. This enables the simplified xmas tree to provide all of the functions of a traditional xmas tree. In addition, the xmas tree can be readily assembled or the tree cap removed from the xmas tree to receive a BOP stack for use in the workover mode. A further advantage is that the dual valve xmas tree insert provides well barriers in accordance with statutory offshore requirements.



Claims
  • 1. A xmas tree for use in a variety of well applications, said xmas tree comprising:a generally cylindrical xmas tree housing defining a generally cylindrical bore, a separate xmas tree valve block disposed within the cylindrical bore of said xmas tree housing and engaged with the xmas tree housing, and a xmas tree cap for engaging with one of said valve block, and said xmas tree housing, the xmas tree cap being coupled to a rig via various flowline and umbilical services to facilitate control of the xmas tree in conveying fluids between surface mounted process facility and a downhole reservoir, the xmas tree valve block having a main production bore and at least one auxiliary bore, the main production bore having at least two valves axially spaced therein, said valves being operable to seal the main production bore and provide well barriers, said at least one auxiliary bore providing an annulus access bore and containing a single valve operable to seal the access bore and provide a well barrier in the annulus access bore.
  • 2. A xmas tree as claimed in claim 1 wherein the xmas tree valve block has a main production bore and two auxiliary bores.
  • 3. A xmas tree as claimed in claim 2 wherein one auxiliary bore provides the annulus access bore and has a valve therein and the other auxiliary bore has no valve but is used for receiving a power cable for driving an electrical submersible pump.
  • 4. A xmas tree as claimed in claim 3 wherein the housing engages with a standard wellhead connector to enable it to be attached to a sub-sea wellhead and the valve block is proportioned and dimensioned to fit in within the bore of the housing and the housing is adapted to be received by the tree cap so that connection is made between parts of the production bore, and parts of the two auxiliary bores to provide effective connection for these bores.
  • 5. A xmas tree as claimed in claim 4 wherein the connections in the production and annulus bore are provided by hollow pin and socket connections.
  • 6. A xmas tree as claimed in claim 2 wherein if no power cable is used one auxiliary bore is blocked and the other auxiliary bore is provided with a valve for annulus control.
  • 7. A xmas tree as claimed in claim 1 wherein said at least two axially spaced valves in the production bore are ball valves.
  • 8. A xmas tree as claimed in claim 1 wherein said valves are flapper valves, disc valves or plug valves.
  • 9. A xmas tree as provided in claim 1 wherein separate locking means are provided between the xmas tree housing and the valve block assembly which are actuated when the tree cap fits on to the valve block to lock the valve block to the xmas tree housing, and to provide fine alignment between the tree cap and the housing.
  • 10. A xmas tree as claimed in claim 9 wherein the locking means are radially acting dogs which are actuated by axial movement of a ring within the locking means.
  • 11. A xmas tree as claimed in claim 1 wherein an external surface of the upper end of an valve block is provided with at least one shaped keyway to ensure correct angular alignment between the xmas tree and the tree cap to facilitate correct engagement of various connections at the top surface of the tree cap.
  • 12. A xmas tree as claimed in claim 1 wherein the xmas tree housing is coupled to a guide frame which is adapted to guide and receive the tree cap when installed to facilitate coupling between the tree cap and the tree housing and valve block.
  • 13. A xmas tree as claimed in claim 12 wherein there is provided a permanent guide base, attached to the wellhead system, including a side guide frame with guidepost spacing of the same dimensions as the guide frame coupled to the wellhead so that when the tree cap is removed for workover mode, the tree cap can be moved to one side and parked adjacent to the wellhead.
  • 14. A xmas tree structure comprising:a xmas tree housing coupled to a sub-sea wellhead; a xmas tree valve block located in said xmas tree housing, said xmas tree valve block having a production bore with at least two valves disposed in series and at least one auxiliary bore for facilitating annulus access control, said at least one auxiliary bore having a valve therein, a xmas tree cap coupled to the xmas tree valve block and to said xmas tree housing, locking means disposed in said xmas tree to fasten the xmas tree housing, xmas tree valve block and said xmas tree cap together, said respective xmas tree valves being remotely operable to be selectively moved between an open and a closed position to control flow of liquid through said xmas tree structure.
  • 15. A xmas tree structure as claimed in claim 14 wherein there are two auxiliary bores; one being an annulus access bore with at least one valve therein and the other auxiliary bore for receiving a power cable for supplying power to a downhole electrical submersible pump (ESP).
  • 16. A method of installing the xmas tree on a wellhead for use in a variety of well tests, the tree housing having a blow-out preventer stack initially coupled thereto in place of a tree cap, said method comprising the steps or:a) providing a xmas tree housing coupled to the wellhead, the xmas tree housing having a top part adapted to be coupled to the blow-out preventer connector, b) running a xmas tree valve assembly through said blow out preventer stack for engaging with the xmas tree housing and being operable for providing a well barrier to the flow of well fluid, c) closing the well barrier to provide well isolation once the xmas tree valve assembly is located in said xmas tree housing, d) removing the blow-out preventer stack from the xmas tree housing, e) running in a xmas tree cap and securing the xmas tree cap to the xmas tree housing and xmas tree valve assembly to provide coupling from production and annulus bores to the surface and from auxiliary ports and bore to the surface, the arrangement being such that the valves in the production and annulus bores can be controlled to provide control of well fluid and xmas tree functionality.
  • 17. A method as claimed in claim 16 wherein the method includes the step of using the xmas tree in a workover mode, said method including the additional steps of removing the xmas tree cap and parking the xmas tree cap on a further guide frame adjacent to the wellhead and xmas tree housing, and coupling the blow-out preventer stack on top of said xmas tree housing with said xmas tree assembly contained therein.
Priority Claims (1)
Number Date Country Kind
9613467 Jun 1996 GB
PCT Information
Filing Document Filing Date Country Kind 102e Date 371c Date
PCT/GB97/01680 WO 00 1/11/1999 1/11/1999
Publishing Document Publishing Date Country Kind
WO97/49892 12/31/1997 WO A
US Referenced Citations (7)
Number Name Date Kind
3834460 Brun et al. Sep 1974
4721163 Davis Jan 1988
4749045 Gano Jun 1988
4784225 Peterson Nov 1988
5213162 Iato May 1993
5873415 Edwards Feb 1999
6015013 Edwards et al. Jan 2000
Foreign Referenced Citations (3)
Number Date Country
2038906 Jul 1980 GB
2267920 Dec 1993 GB
9711252 Mar 1997 WO