Wells – Submerged well – Connection or disconnection of submerged members remotely...
Reexamination Certificate
2000-11-29
2002-12-17
Bagnell, David (Department: 3672)
Wells
Submerged well
Connection or disconnection of submerged members remotely...
C166S368000
Reexamination Certificate
active
06494267
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wellhead assembly for accessing an annulus within a well, especially a subsea well, in particular an annulus between adjacent casing strings within the well. The present invention further relates to a method of accessing an annulus within a well, in particular a subsea well, and the use of the method in the injection of fluids into the well or the production of fluids from the well.
BACKGROUND OF THE INVENTION
A range of well operations requires access to an annulus between adjacent casing strings within the well. For example, it is often required to produce or displace fluids from the well through such an annulus, such as when drilling operations are underway. In addition, it is also a known practice to inject fluids into the well and underground formations into which the well extends through such an annulus. One operation involving such an injection of fluid is the disposal of cuttings.
The drilling of an oil or gas well, for example a subsea well, results in the formation of small fragments of rock and other matter, known as cuttings, from the various formations through which the-well is drilled. The cuttings are removed from the well as they are formed by the drill bit by being entrained in a drilling mud pumped down the well and returned to the surface vessel or platform. The cuttings are typically recovered from the drilling mud by a separation process and the mud reused in the well operations. In the past, at offshore locations, it has been common practice to dispose of the cuttings separated from the drilling mud in this way by dumping them in the sea. This practice has proven acceptable in the past, as the environmental impact from the negligible amounts of entrained oil based mud in the cuttings was low. Additionally, may companies have changed their practice to use synthetic drilling mud that is environmentally friendly.
Recently, however, it has become favored to employ oil based drilling muds, as such mud formulations offer a number of advantages. For example, oil based muds improve the stability of the well bore, improve the performance of the drill bit by providing better lubrication and removal of cuttings as they are formed, and reduce the torque generated in the drill string during use. For these reasons, oil based drilling muds have been finding increasing use. While offering advantages during the drilling operation, the oil based mud formulations present a problem with respect to disposal. Cuttings separated from the oil based muds after recovery from the well are inevitably contaminated with the oil based formulation. Washing the cuttings has been attempted, but only removes the mud from the surface of the cuttings particles, leaving oil in the cracks and pores of the fragments. It is no longer possible to dispose of cuttings recovered from an offshore well using oil based drilling muds in the same manner as when water based muds are employed by simply pouring the cuttings into the sea, as the cuttings give rise to an adverse environmental impact. The corresponding environmental regulations have become more stringent year by year, decreasing the allowable quantities of entrained oil based mud present in the washed cuttings.
Accordingly, it has been the practice to dispose of the cuttings by injecting them into a well and into subsurface formations. To facilitate this, it has been the practice to grind the cuttings and suspend them in a suitable liquid to form a pumpable slurry, which may then be injected into a subsurface formation through an annulus between adjacent casings in the well. This has been common practice in environmentally sensitive areas, such as the north slope of Alaska, for many years.
US Pat. No. 4,942,929 discloses a method for the disposal and reclamation of drilling wastes, in which construction grade gravel is separated from drilling cuttings produced during well drilling operations. The solids that are not so recovered are formed as a slurry with the remaining clays, silts and spent drilling fluid and conducted to a second well, remote from the well being drilled, into which the slurry is injected. Centrifugal pumps or mechanical agitators are used to disperse the fine solids in the slurry to assist in the injection process.
A drill cuttings disposal method and system are disclosed in U.S. Pat. No. 5,129,469. In the method and system disclosed, drill cuttings produced during well drilling operations are brought to the surface and separated from the drilling mud, mixed with a suitable liquid, such as sea water and the mixture subjected to grinding to form a slurry. The slurry may then be pumped into a selected zone of the well for disposal.
U.S. Pat. No. 5,341,882 discloses a method for the disposal of well drilling cuttings, in which the cuttings are solidified by combining the cuttings with water and blast furnace slag. The resulting mixture is injected into the annulus between two wellbore casings, where it solidifies to form a cement.
U.S. Pat. No. 5,884,715 discloses a method and apparatus for injecting cuttings into a well while drilling operations are in progress. Two embodiments are discussed in the disclosure. The first method requires a predrilled well bore to be bored adjacent to and extending away from the well being drilled. The predrilled well bore is used as a depository for the drilling cuttings produced from the well being drilled. The second embodiment requires an injection tube to be installed within the well being drilled alongside the casings set into the well, through which access can be gained to subsurface formations into which the cuttings may be injected. A further embodiment employs an annulus between adjacent casings in the well in order to gain access to underground formations. It is noted that the embodiments disclosed in U.S. Pat. No. 5,884,715 relate to the injection of cuttings into a well having a wellhead accessible on land. While subsea operations are mentioned, little information is given regarding the injection of cuttings into subsea wells.
A subsea wellhead typically comprises a conductor pipe extending below the sea bed in the well, the upper portion of which extends from the well and forms a conductor housing. A high pressure housing is landed in the conductor housing, on which is typically mounted a blowout preventer (BOP) stack by means of a BOP guide funnel. Successively smaller casings are landed in the wellhead, suspended from casing hangers secured within the conductor pipe or the high pressure housing. The pressure boundary region of the wellhead assembly is that region of the assembly between the first or upper end of the high pressure housing and the lowermost casing hanger seal assembly. A guide base is often employed, which comprises a structure extending around the wellhead and mounted to the conductor housing.
A subsea well injection system is disclosed in U.S. Pat. No. 5,085,277, for injecting unwanted slurries and other fluids arising from drilling or other downhole operations into a subsea well. The slurry or other fluid is injected through a drilling guide base positioned around the well on an underwater surface. The system employs a dedicated guide base, which comprises pipework on the guide base leading to a port in the conductor casing of the well, thus gaining access to the annulus between the conductor casing and the adjacent inner casing. A fail safe isolation valve is provided on the guide base and joined to the pipework. A coupling is provided to connect the isolation valve to a surface vessel or platform. The wellhead is modified to provide a port in the housing, in order to gain access to an annulus between casings within the well. With a single port in the outermost casing of the well, fluids may be injected into the outermost annulus of the well. If access is required to an inner annulus, similar ports are required in the casings disposed radially outwards of the inner annulus to provide a flow path to the pipework extending from the guide base.
In U.S. Pat. No. 5,339,912, there is disclosed a cut
Bagnell David
Bielinski Peter A.
Cooper Cameron Corporation
Duke Jackie L.
Hartmann Michael P.
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