Systems and methods for constructing subsea production wells

Details Systems and methods for constructing subsea production wells Systems and methods for constructing subsea production wells

2002-06-17

2004-01-06

Pezzuto, Robert E. (Department: 3671)

Wells

Submerged well

Connection or disconnection of submerged members remotely...

C166S345000, C166S352000, C166S358000, C405S224200

Reexamination Certificate

active

06672390

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to systems and methods for constructing wells in marine environments. In another aspect, the present invention relates to systems and methods for constructing marine wells comprising use of a surface blowout preventer stack (SBOP). In even another aspect, the present invention relates to systems and methods for constructing marine wells, wherein the methods and systems comprise use of an SBOP and a drill thru Xmas (Christmas) tree. In still another aspect, the present invention relates to systems and methods for constructing marine wells, wherein the systems and methods comprise use of an SBOP, high pressure risers, a subsea shut off and disconnect device, and a drill thru Xmas tree.
2. Description of the Related Art
Exploration and production of hydrocarbons from subsea reservoirs is an expensive and time-consuming process. The drilling and production processes used to obtain hydrocarbon products from subsea wells often require allocation of expensive assets, such as floating drilling and production facilities located offshore. There are a number of problems associated with deepwater offshore drilling and production that are not found in shallow water or land operations.
Primary among these is the marine environment. Unlike the surface environment, much of the deepwater offshore drilling control equipment is located on the seabed and is not subject to direct control and monitoring—one simply cannot see the equipment without the use of vision equipped remotely operated vehicles (ROVs).
The mechanics of drilling in a marine environment also differ from land operations. Drilling operations utilize a weighted drilling fluid, known as mud which is pumped down the drill string and circulated back to the surface through an annulus between the drill string and the borehole wall. The drilling mud cools the drill bit as it rotates and cuts into the earth formation. The mud also provides a medium for returning the cuttings created by the drill to the earth's surface via the annulus. The weight of the drilling mud in the annulus further operates to control pressure in the borehole and help prevent blowouts. Also, additives in the mud are designed to form a cake on the inside walls of the borehole in order to provide borehole stability and to prevent formation fluids from entering the borehole prior to production operations. It will be appreciated that during land operations, the drilling mud and cuttings may be readily returned to the surface via the borehole annulus. Such is not the case in offshore operations.
Offshore operations require location of a floating drilling unit in waters located generally above the reservoir of interest. The depth of the water may range from several hundred feet to depths greater than a mile. A drill string must travel from the surface of the drilling platform, down to the equipment located on the seabed, and then into the bore of interest prior to actually initiating cutting/drilling operations. Unlike land operations, there is no annulus between the floor of the seabed and the drilling platform at the surface. Accordingly, a drilling riser comprised of generally cylindrical elements is provided for and extends from a wellhead located at the seabed up to the drilling platform located above the surface of the water. The riser operates to protect the drill string during operations and acts as an artificial annulus.
The risers are formed from large diameter (on the order of 21 inches) metal tubular goods/joints linked together. Riser joints may be 75 feet or more in length. Buoyancy elements, also called floats, may be affixed to the external surface of the drilling riser along its length in order to establish essentially neutral buoyancy. It is possible that multiple buoyancy elements may be affixed to a single riser joint. The foam floats may be affixed about the riser by any of a number of ways as will be discussed with reference to preferred embodiments of the present invention. The buoyancy elements are often manufactured from syntactic foam or metal, and are generally 6 to 12 feet in length. The specific foam chemistry and diameter of the float are selected in accordance with the specific environmental conditions to be encountered in operations. Typically, the buoyancy elements are manufactured onshore and shipped to the drilling platform, and are usually installed on the riser prior to riser installation.
As with land drilling operations, subsea drilling operations must provide a means for shutting down the well in emergency situations. Generally, a series of blowout preventers (BOPs) referred to as a BOP stack, are used to control well flow in such instances. The BOP stack typically consists of multiple BOPs connected to each other and to the wellhead, and may include shear ram or annular BOPs. In land operations, the BOP stack is typically just below the rotary table and may be easily monitored and operated in response to a significant well event. However, in conventional subsea drilling systems the BOP stack is located on the seafloor and requires various umbilical and control lines in order to monitor conditions and operate the BOP stack. It will be appreciated that similar to the drill string and drilling riser, the umbilical and control lines must traverse the distance between the offshore platform and the subsea wellhead.
The riser, umbilicals, control lines and other subsea elements, including buoyancy elements, are subjected to ocean currents along their respective lengths, causing lateral deflection in the riser from the seabed to the surface platform. A riser and control lines may be subjected to varying and differential ocean currents along its length resulting in complex lateral deflection of the riser and can result in a number of problems. Continued deflection of a riser may result in stress points along the length of the rise and ultimately weaken the riser. Radical lateral deflection in the riser could result in excessive drill string contact with the inner wall of the riser, resulting in further weakening of the riser.
Metaocean conditions, such as winter storms, hurricanes and typhoons add yet another element of complexity to offshore drilling operations. During such events, drilling operations are typically suspended and the crew is evacuated. In the case of fixed offshore platforms or compliant tower platforms, the riser is often left in place as it is supported by a conductor system that extends from near surface to near sea bed. Floating offshore platforms present different problems in that there are no conductors to support the riser system, which depends instead, on a combination of flotation cells and topside tensioners for support. Should a metaocean condition occur, the crew is similarly evacuated, leaving the riser system subject to current stresses, as well as wind and wave stresses placed on the floating platform. To prevent damage from occurring, the riser system is often disconnected from the sea floor BOP stack and tripped, together with the control lines, to the platform surface. After the condition abates, the riser system, as well as the umbilicals and control lines are then reconnected to the sea floor BOP stack and a series of time-consuming safety tests are performed before drilling can resume.
It will be appreciated that the time required to disconnect and subsequently reconnect the riser system results in significant loss of rig time, particularly in the case of offshore platforms. Reconnection typically includes running the riser and associated umbilicals down to the seafloor BOP stack, and these are typically reconnected utilizing ROVs. The reconnection process can take many hours, followed by days of testing. Thus, there exists a need for time- and cost-effective means of disconnecting and reconnecting drilling riser systems.
Also, using conventional subsea BOP equipment, critical rig time is required to run, set and retrieve the subsea BOP and its accessories. There is correlation between the depth of the water and th

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