Wells – Submerged well – Connection or disconnection of submerged members remotely...
Reexamination Certificate
1999-01-11
2001-05-08
Lillis, Eileen D. (Department: 3673)
Wells
Submerged well
Connection or disconnection of submerged members remotely...
C166S368000
Reexamination Certificate
active
06227301
ABSTRACT:
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 s
Edwards Jeffrey Charles
Morgan Michael Graham
Expro North Sea Limited
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Lagman Frederick L.
Lillis Eileen D.
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