Standard Oil Company (indiana)

William D Greenfield

Johnce E Hall

Kenneth A Blenkarn

The riser pipe, e.g., 21 inches in diameter, extends from the ship to an anchored wellhead assembly on the ocean floor. A drill bit and drill string are guided down through the inside of the riser pipe and the anchored wellhead assembly to perform drilling operations in the ocean floor. Various strings of casing for lining the borehole wall, which is thus drilled, are run down through the interior of the riser pipe. The first string of casing run is of relatively large diameter, e.g., 20 inches in diameter followed by 133/8 or 103/4 strings. Intermediate strings are typically 95/8 or 75/8, depending on the previous string diameters. As heavier drilling muds are used, the riser tension needed to prevent buckling is increased. To reduce the tension required, we place a sleeve of low density in the annulus between the drill string and the riser pipe interior wall, leaving a much smaller annulus between the drill pipe and the insert, thus displacing the heavier mud with a lighter weight insert.

Riser pipe inserts

This invention relates to the installation of a Vertically Moored Platform and equipment and apparatus used in effecting such installation. The floating structure, anchored only by essentially parallel and vertical elongated members under tension, is positioned with a gravity base over the subsea well site. The gravity base is lowered from engagement with the floating structure with cables to the sea floor while maintaining the floating structure in a positive buoyancy state. A large-diameter drive pipe is inserted through each receiving passage in the gravity base and into the soil or rock beneath the gravity base where it is anchored. A conductor is inserted through the drive pipe and anchored or cemented to the soil or rock beneath the drive pipe. A riser pipe is then inserted into the drive pipe and secured to the conductor. The upper end of the riser pipe is secured to the floating structure. Up to 32 or more such risers are connected between the floating structure and the gravity base. The riser pipes are then placed under tension and the cables used to lower the gravity base are then removed. Drilling operations then proceed through each of the risers. Modification of this installation and equipment necessary therefor are described.

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Tulsa, OK, United States of America

William D Greenfield