Wells – Submerged well – Wellhead
Reexamination Certificate
1998-03-26
2001-09-25
Bagnell, David (Department: 3673)
Wells
Submerged well
Wellhead
C166S345000, C166S360000
Reexamination Certificate
active
06293345
ABSTRACT:
This invention relates generally to apparatus for use in drilling and completing subsea wells of the type in which a blowout preventer (BOP) stack is positioned on a floating rig and is connected to the head of the well by a high pressure riser. More particularly, it relates to improvements in apparatus of this type in which the flow of well fluid between the tubing/casing annulus within the well and equipment above the wellhead is controlled by valve means within passageway means in the wellhead, and, if desired, in which operating fluid to or from a downhole function, such as a tubing safety valve, flows through a passageway means connecting to a subsea Christmas tree or a production riser connector leading to a surface tree.
In apparatus of the type in which the Christmas tree is installed on the wellhead so as to produce the well at the subsea level, flow between the tubing/casing annulus and the tree is typically controlled by an “annulus safety valve” installed in passageway means in a tubing hanger suspended within the wellhead housing. See, for example, U.S. Pat. Nos. 5,143,158 and 5,687,794, both assigned to the Assignee of the present Application. Other downhole functions, such as opening or closing subsurface tubing safety valves, are often controlled by operating fluid transmitted to or exhausted from the valves or other functions through additional passageways within the tubing hanger.
In the drilling and completion of a subsea well of the type contemplated by this invention, a relatively large diameter, low pressure drilling riser is normally used in the early drilling stages, and a relatively small diameter, high pressure production riser is used during the installation of production casing and/or production tubing, the use of smaller diameter risers of course reducing costs. This could perhaps be accomplished with a single wellhead housing, without resort to large diameter production risers, by landing a small diameter production tubing hanger in a sleeve installed within the bore of the wellhead housing. However, because of physical restraints, it would be impossible to control the flow of well fluid in the annulus or the flow of control or operating fluid through the tubing hanger.
In accordance with the novel aspects of the present invention, a wellhead housing adapted to be installed on a subsea well has a relatively large diameter lower bore portion and a relatively small diameter upper bore portion which provides a relatively thick wall thereabout, a casing hanger is adapted to be lowered into and landed within the lower bore portion of the wellhead housing to suspend a production casing string within the well, and a tubing hanger is adapted to be lowered into and landed within the upper bore portion of the wellhead housing in order to suspend a production tubing string within the production casing string. More particularly, the portion of the wellhead housing which surrounds the upper bore portion is sufficiently thick that passageway means may extend therein from a lower end connecting with the annulus between the casing and tubing strings and an upper end connecting with the upper end of the wellhead housing, and then with a tree or production riser thereabove, and remotely operable valve means may be installed in the passageway means to control flow between the annulus and the upper end of the wellhead housing. Moreover, additional passageway means may extend within this relatively thick wall of the housing to connect equipment above the upper end of the housing with a conduit extending through the annulus and through which control fluid may flow to control a safety valve for the tubing or other downhole function.
Tubular members known as “spools” are often installed on wellhead housings when it is decided to complete or workover the well. Among other things, they add vertical space to the wellhead. Additionally, they assist in resisting bending moments imposed on the wellhead. Normally, the spools have the same I.D. as the bore of the wellhead housing on which they are installed. In accordance with another novel aspect of the invention, the wellhead housing includes a casing head in which the lower bore portion is formed and in which the casing hanger is landed, and a spool above the casing head in which the upper bore portion is formed and in which the tubing hanger is landed above the casing hanger.
In the preferred and illustrated embodiment of the invention, a first, relatively large diameter, low pressure drilling riser is lowered onto and releasably connected to the upper end of the casing head, prior to lowering and landing of the casing hanger therein, and a second, relatively small diameter, high pressure drilling riser is lowered onto and releasably connected to the upper end of the spool, following removal of the first riser to permit lowering and landing of the casing hanger. The tubing hanger has passageways which, upon landing of the tubing hanger within the spool, are aligned for connection with passageway means in the spool through which control fluid may pass to or from a downhole function.
In accordance with one embodiment of the invention, wherein the well is to be produced through a Christmas tree at the surface, the second riser is removed and replaced by a high pressure production riser which is lowered onto and releasably connected to the upper end of the spool, upon lowering and landing of the tubing hanger therein. More particularly, the means for releasably connecting the production riser to the spool includes a connector body having passageway means for connecting the upper end of the passageway means in the spool with a conduit leading to the surface.
In accordance with an alternative embodiment of the invention, wherein the well is to produced at the subsea level, a Christmas tree is lowered onto and releasably connected to the upper end of the spool following removal of the high pressure drilling riser and landing of the tubing hanger within the spool. More particularly, the Christmas tree is connected to the spool by a connector body having passageway means therein for connecting the upper end of the spool passageway means with means a valve controlled passageway in the tree.
REFERENCES:
patent: 4632188 (1986-12-01), Schuh et al.
patent: 4726424 (1988-02-01), Raulins
patent: 5143158 (1992-09-01), Watkins et al.
patent: 5213162 (1993-05-01), Iato
patent: 5280766 (1994-01-01), Mohn
patent: 5544707 (1996-08-01), Hopper et al.
patent: 5687794 (1997-11-01), Watkins et al.
patent: 5735344 (1998-04-01), Duncan
patent: 0373766A2 (1990-06-01), None
patent: 2291085A (1996-01-01), None
Bagnell David
Browning & Bushman P.C.
Dril-Quip Inc.
Kreck John
LandOfFree
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