In the drilling of offshore petroleum or gas producing wells from a fixed platform it is customary to insert a conductor member into the marine structure between the work deck and the wellhead. This conductor serves the primary purpose of enclosing the rotating drill string. Thus, drilling mud can be circulated through the drill string and returned to the pumps on the working deck.
In some instances where the petroleum-bearing reservoir is determined to be relatively close to the surface of the water, it is necessary to offset the rotating drill string rather quickly so it will assume a desired direction whereby to enter the reservoir. In shallow areas this offsetting of the drill string from vertical must be accomplished as soon as possible so that the drill will intersect the reservoir within a short period of time.
It is known that by initially deflecting the drill string such that it enters the ocean floor at a desired angle, the operation is expedited. In one method of achieving such directional drilling, the conductor is positioned within the offshore structure and initially aligned at an angle to the structure floor. Thus, the drill string, by being guided through the conductor, will enter the floor at a predetermined angle and direction.
It is also known that to effectuate the desired offset, the drill string can be initially forced from a vertical disposition into the desired entry angle. This is normally done through use of an elongated conductor guide which is carried within the body of a marine platform.
The guide comprises a heavy walled tube-like member which is performed into a desired curved configuration. The addition of curved or straight guide members to the underwater section of a marine structure after it has been placed at an offshore site is usually an expensive operation requiring the use of divers and other special equipment.
The instant invention therefore provides a novel arrangement in an offshore structure which serves the purpose of facilitating a directional drilling operation. It further serves to reduce overall operating expenses and provides the structure with a greater degree of versatility due to the greater number of wells that can be drilled from a single position. It also permits the positioning of drill conductor guides by suspending a drill conductor guide cage outboard of the structure, thereby avoiding the need for the cage to take up valuable deck space.
The marine structure presently contemplated is thus provided with ordinary drilling equipment such as derrick, rotary table and the like. However it is also provided with an elongated cage or substructure which serves as an underwater support member for a number of conductor guides. The cage can be detached from its normal submerged position in the marine structure and raised to the working deck. The cage is further provided with means for pivotally swinging the entire unit outboard of the working deck and into a substantially horizontal position which facilitates its being worked on.
Thus, the number of, or the pattern of conductor guides can be changed by addition to or removal of said guides to achieve a desired pattern at the ocean floor. The cage therefore will be swung back on board the platform and into a vertical position prior to being reinserted by lowering into its normal seating or working position. Thus, the original conductor guides, or the newly inserted guides, are aligned to permit further drilling in a particular direction from an initially upright disposition of the drill string.
It is therefore an object of the invention to provide a marine structure capable of drilling wellbores into the ocean floor and exhibiting great drilling versatility. A further object is to provide the marine drilling apparatus of the type contemplated which is particularly adept at drilling directionally away from a working site. A still further object is to provide an underwater drilling structure which can be conveniently worked on when it is raised to an above-water position adjacent to a marine platform's working deck.