Wells – Submerged well – Means removably connected to permanent well structure
Reexamination Certificate
2001-11-30
2003-04-29
Pezzuto, Robert E. (Department: 3671)
Wells
Submerged well
Means removably connected to permanent well structure
C166S346000, C166S367000, C405S224200, C405S224400
Reexamination Certificate
active
06554072
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to offshore drilling and production operations and is specifically directed to drilling and production tensioners and risers assembled using the tensioners.
2. Description of Related Art
A marine riser system is employed to provide a conduit from a floating vessel at the water surface to the blowout preventer stack or, production tree, which is connected to the wellhead at the sea floor. A tensioning system is utilized to maintain a variable tension to the riser string alleviating the potential for compression and in turn buckling or failure.
Historically, conventional riser tensioner systems have consisted of both single and dual cylinder assemblies with a fixed cable sheave at one end of the cylinder and a movable cable sheave attached to the rod end of the cylinder. The assembly is then mounted in a position on the vessel to allow convenient routing of wire rope which is connected to a point at the fixed end and strung over the movable sheaves. A hydro/pneumatic system consisting of high pressure air over hydraulic fluid applied to the cylinder forces the rod and in turn the rod end sheave to stroke out thereby tensioning the wire rope and in turn the riser.
The number of tensioner units employed is based on the tension necessary to maintain support of the riser and a percentage of overpull which is dictated by met-ocean conditions i.e., current and operational parameters including variable mud weight, etc.
Normal operation of these conventional type tensioning systems have required high maintenance due to the constant motion producing wear and degradation of the wire rope members. Replacing the active working sections of the wire rope by slipping and cutting raises safety concerns for personnel and has not proven cost effective. In addition, available space for installation and, the structure necessary to support the units including weight and loads imposed, particularly in deep water applications where the tension necessary requires additional tensioners poses difficult problems for system configurations for both new vessel designs and upgrading existing vessel designs.
Recent deepwater development commitments have created a need for new generation drilling vessels and production facilities requiring a plethora of new technologies and systems to operate effectively in deep water and alien/harsh environments. These new technologies include riser tensioner development where direct acting cylinders are utilized.
Current systems as manufactured by Hydralift employ individual cylinders arranged to connect one end to the underside of the vessel sub-structure and one end to the riser string. These direct acting cylinders are equipped with ball joint assemblies in both the rod end and cylinder end to compensate for riser angle and vessel offset. Although this arrangement is an improvement over conventional wire rope systems, there are both operational and configuration problems associated with the application and vessel interface. For example, one problem is the occurrence of rod and seal failure due to the bending induced by unequal and non-linear loading caused by vessel roll and pitch. Additionally, these systems cannot slide off of the wellbore centerline to allow access to the well. For example, the crew on the oil drilling vessel is not able to access equipment on the seabed floor without having to remove and breakdown the riser string.
The tensioner system of the present invention is an improvement over existing conventional and direct acting tensioning systems. Beyond the normal operational application to provide a means to apply variable tension to the riser, the system provides a number of enhancements and options including vessel configuration and its operational criteria.
The tensioner system has a direct and positive impact on vessel application and operating parameters by extending the depth of the water in which the system may be used and operational capability. In particular, the system is adaptable to existing medium class vessels considered for upgrade by reducing the structure, space, top side weight and complexity in wire rope routing and maintenance, while at the same time increasing the number of operations which can be performed by a given vessel equipped with the tensioner system.
Additionally, the present invention extends operational capabilities to deeper waters than conventional tensioners by permitting increased tension while reducing the size and height of the vessel structure, reducing the amount of deck space required for the tensioner system, reducing the top-side weight, and increasing the oil drilling vessel's stability by lowering its center of gravity.
Moreover, the tensioner of the present invention is co-linearly symmetrical with tensioning cylinders. Therefore, the present tensioner eliminates offset and the resulting unequal loading that causes rapid rod and seal failure in some previous systems.
The tensioner of the present invention is also radially arranged and may be affixed to the vessel at a single point. Therefore, the tensioner may be conveniently installed or removed as a single unit through a rotary table opening, or disconnected and moved horizontally while still under the vessel.
The tensioner of the present invention further offers operational advantages over conventional methodologies by providing options in riser management and current well construction techniques. Applications of the basic module design are not limited to drilling risers and floating drilling vessels. The system further provides cost and operational effective solutions in well servicing/workover, intervention and production riser applications. These applications include all floating production facilities including, tension leg platform (T.L.P.) floating production facility (F.P.F.) and production spar variants. The system when installed provides an effective solution to tensioning requirements and operating parameters including improving safety by eliminating the need for personnel to slip and cut tensioner wires with the riser suspended in the vessel moonpool. An integral control and data acquisition system provides operating parameters to a central processor system which provides supervisory control.
The present invention is also directed to a method of assembling a string of production riser, or production riser, for drill stem testing while the larger string of drilling riser, referred to herein as the drilling riser, is still suspended from the vessel, and preferably, still connected to the wellhead. Therefore, the amount of time, and thus money, required to prepare for the drill stem test is substantially reduced. While the background of method of assembling a production riser will be discussed in greater detail, it is to be understood that the methods of the present invention include assembling a drilling riser.
Generally, a well is first drilled from a drilling vessel or drilling platform having one or more derricks for supporting the drilling riser and other drilling equipment. After drilling is completed, the well is “closed off” using valves or other equipment. The drilling riser is then disassembled. The production riser is then assembled, usually utilizing the same derrick and equipment. This is especially true in vessels having only one fill size derrick that can support the weight of the riser. Both the drilling riser and the production riser consist of tubulars, e.g., casing, attached end to end and extended from the wellhead to the drilling or production facility, e.g., vessel or platform.
Alternatively, in drilling vessels having two derricks, the second derrick may be utilized to assemble the production riser. After the production riser is assembled, it is attached to the wellhead and a drill stem test is performed. The drill stem test is an evaluation of unrestricted flow of hydrocarbon, e.g., oil or gas, from the well and into shipboard tanks to facilitate determining the hydrocarbon reservoir's size and propensity to flow, e.g., the pressure differen
Mournian Timothy I.
Reynolds Graeme E.
Andrews & Kurth L.L.P.
Beach Thomas A.
Control Flow Inc.
Matheny Anthony F.
Pezzuto Robert E.
LandOfFree
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