Wells – Submerged well – Wellhead
Reexamination Certificate
2000-11-29
2002-11-26
Bagnell, David (Department: 3672)
Wells
Submerged well
Wellhead
C166S089100
Reexamination Certificate
active
06484807
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wellhead assembly for injecting a fluid, in particular a slurry of cuttings from a well drilling operation, into a well and a method for its use. The well is especially a subsea well. The method and apparatus of the present invention may be applied in, but are not limited to, the disposal of drilling muds and drilling cuttings prepared in the form of a liquid slurry.
BACKGROUND OF THE INVENTION
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 drilling muds employed were water based in composition and, as such, cuttings separated from such water based slurries gave rise to minimal, if any, environmental impact when disposed of in the aforementioned manner. Additionally, many companies have changed their practice to use synthetic drilling mud that is environmentally friendly.
Recently, however, it has become favoured 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. Cutting 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, due to a damaging environmental impact. The corresponding environmental regulations now prohibit this method of disposal.
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.
U.S. 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 cutting disposal method and system is 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. 5,255,745 describes a method and apparatus for providing a remotely operable connection to establish access to an annulus within a wellhead assembly. The apparatus requires a port in the wellhead assembly. A valve is positioned to seal with the port by remote means using a ramp assembly supported on a guide base positioned around the wellhead.
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. 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 housing 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 conductor housing, in order to gain access to an annulus between casings within the well. With a single port in the outermost housing 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 cuttings disposal system in which an injection adapter is employed to allow a slurry of cuttings to be injected into a well. The well, designated an “injection well”, has an inner and an outer wellhead housing with at least one casing hanger and a respective inner casing installed in the inner wellhead housing. The casing hanger
Bagnell David
Bielinski Peter A.
Cooper Cameron Corporation
Duke Jackie L.
Hartmann Michael P.
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