Abstract: A system for drilling a subsea well from a rig through a subsea wellhead below the rig includes a wellhead stack which is mounted on the subsea wellhead. The wellhead stack includes at least a subsea blowout preventer stack and a subsea diverter. A drill string extends from the rig through the wellhead stack into the well to conduct drilling fluid from the rig to a drill bit in the well. A riser which has one end coupled to the wellhead stack and another end coupled to the rig internally receives the drill string such that a riser annulus is defined between the drill string and the riser. A well annulus extends from the bottom of the well to the subsea diverter to conduct fluid away from the drill bit. A pump has a suction side in communication with the well annulus and a discharge side in communication with the rig and is operable to maintain a selected pressure gradient in the well annulus.

Abstract: A Heave-Restrained Platform and Drilling System (HRP/DS) comprises a floating structure having a central buoyance means, at least three out-rigger columns, and a hybrid mooring system in which a spread (lateral) mooring system functions with an array of tensioned production risers (serving as a vertical tension leg) to keep the structure generally over a specified seabed location. The central buoyancy means has supports for upper terminations of a plurality of well production risers. Each riser is comprised of plural concentric tubular structural and pressure containment elements connecting a hydrocarbon well on the sea floor with a pressure containment means located on the floating structure.

Abstract: A Heave-Restrained Platform and Drilling System (HRP/DS) comprises a floating structure having a central buoyancy means, at least three out-rigger columns, and a hybrid mooring system in which a spread (lateral) mooring system functions with an array of tensioned production risers (serving as a vertical tension leg) to keep the structure generally over a specified seabed location. The HRP/DS provides a means for drilling and producing through oil wells in deep water such that critical pressure containment means are achieved with safe, redundant barriers and systems similar to those employed on shallow water fixed platforms.

Abstract: A tension leg platform which can be a heave restrained platform and drilling system (HRP/DS) is taken to the heave restrained mode by rapidly sluicing ballast by gravitational force from a reservoir above the water line.

Abstract: A subsea drilling template has a plurality of drilling guides disposed at various angles relative to the plane of the template. The drilling guides cause angular deviation of the drill string passing into the guides resulting in wide spacing of the boreholes drilling through the template. The widespread boreholes allow efficient production of shallow subsea hydrocarbon producing formation without the need of satellite wells.

Abstract: A guideline system for positioning subsea equipment utilizes splayed guidelines for exerting lateral forces on the subsea equipment as it is lowered into place.

Abstract: A modular riser tensioner has a frame (10) for mounting on a platform deck with air (16,18) and oil (20,22) accumulators mounted on a mounting frame and connected to cylinders (24-30) also on the mounting frame. A piston (32) located within the cylinders carries a riser tensioning ring (50) for supporting the riser. Pairs of cylinders are located on opposite sides of the riser and connected to an oil accumulator independent of the other cylinders.

Abstract: A well support system is provided including a tubular riser connecting a subsea well to a surface platform. A flexible elastomeric mounting column is providing for supporting the tubular riser from the surface platform. A first support structure supports the lower end of the flexible mounting column from the surface platform. A second support structure supports the tubular riser from an upper end of the flexible mounting column, so that a weight of the tubular riser is supported in compression by the flexible mounting column. The flexible mounting column provides a substantially constant supporting force over a range of compressed displacement corresponding to a range of expected relative movement between the riser and the platform. The flexible mounting column is preloaded in compression to within its constant force output range.

Abstract: Methods and apparatus are provided for temporarily mooring a tension leg platform while the permanent vertical tethering elements thereof are connected between the platform and an anchor located upon the ocean floor.

Abstract: Apparatus and methods for permanently mooring a tension leg platform.

Abstract: Apparatus and methods are provided for installing an underwater anchor system including a plurality of separate anchors for a tension leg platform. A cluster of tethering elements is connected between the tension leg platform and each of the separate anchors. Each anchor assembly includes a primary anchor which is first located approximately in a desired position upon the ocean floor. This position includes a lateral location and/or an angular orientation about a vertical axis. Then the position of the primary anchor is ascertained and compared to a desired position of the main anchor. The main anchor is designed to be lowered into engagement with the primary anchor. A relative position determining structure is interconnected between the primary and main anchors for varying the relative position of the main anchor relative to the primary anchor to correct for any difference between the ascertained final position of the primary anchor and the desired position of the main anchor.

Abstract: A method for drilling wellbores from an offshore platform to penetrate a subterranean formation using a combination of surface drilling techniques and subsea drilling techniques to achieve an improved effectiveness by avoiding the necessity for large conduits communicating the ocean floor and the offshore platform.

Abstract: An improved offshore platform, the platform including three decks in the wellbay area; a first lower deck adapted to provide a workspace for the positioning of equipment to be lowered to the ocean floor, a second middle deck, said middle deck being the main production deck from which production conduits from said wellbores are supported and from which production operations are conducted after completion of said wellbores and a third upper deck said third deck being adapted to support drilling, completion and workover equipment and to provide a protective barrier between said equipment and said second deck.