GB873480A - Improvements in or relating to apparatus for drilling and working in underwater wells - Google Patents

Abstract

873,480. Boring earth. SHELL OIL CO., CONTINENTAL OIL CO., SUPERIOR OIL CO., and UNION OIL CO. OF CALIFORNIA. Sept. 3, 1957, No. 27717/57. Class 85. Subaqueous borehole apparatus comprises a vessel 21, means 24 for anchoring the vessel, a base 18 adapted to be secured to the formation 23 to be bored, a receiver 45B on or co-operating with the base and adapted to overlie the borehole when the base is secured to the formation at the site of the borehole, flexible guides 19 attached to the base, a conductor 92 having sufficient length to extend from the vessel to the formation, and having a lower end adapted to register with the receiver, means 98 to lower the conductor from the vessel, and means 80 engaging the conductor and the guides to cause the conductor to register with the receiver when the base is secured to the formation. The base comprising a framework and buoyancy tanks 53 is floated to the site, the guides are attached to cones 57 on the base, the tanks are flooded, and the base is pulled to the position shown in Fig. 1 beneath the cellar 38 of the vessel. A drill pipe 41 having an under-reamer 44 is run through a central opening in the base and is rotated by apparatus mounted on the vessel to start the borehole, drilling mud or sea-water being pumped down the drill pipe to clear drillings from the hole. After the hole has reached sufficient depth to receive casing 45 welded at its upper end to the base, the base is lowered down the pipe by means of the guides, blow-out preventers 45A at the top of the casing and supporting receiver 45B being held open. The casing is cemented into the hole to secure the base to the formation Where the depth of water is less than the length of the casing required, the base is positioned beneath the cellar without the blow-out preventers, casing and receiver. A length of casing is run through the base, and base and casing are lowered, lengths being added to the casing until the base rests on the formation. The drill is removed when the hole is deep enough to receive the casing, and the casing is run into the hole until the blow-out preventers carrying the receiver and fixed to the upper length of casing rest on the base. The drill is run into the casing, the blow-out preventers are closed, and cement is pumped down the drill pipe to cement the casing to the base. The means 80 encloses an annular seal adapted to engage the receiver, is slidably supported on posts 67 having conical ends 70 adapted to engage the cones 57, and is attached to the lower end of the conductor by a flexible coupling 86. After the base is secured to the formation the guides are threaded through the posts, and the upper ends of the guides are wound round winches mounted on the vessel and powered by torque converters. The conductor is supported by the cable 98 passing round a winch mounted on the vessel and powered by a torque converter, and is lowered, conductor sections together with buoyancy tanks 96 being added until the cones 70 engage the cones 57 and the means 80 rests upon the blow-out preventers. Fluid pressure from a pipe 124 is applied to the seal within the means 80 to seal the conductor to the receiver. Drilling is recommenced, mud from a tank 84A on the vessel being supplied down the drill pipe to the bit, and, being returned through the annular space between the drill pipe and conductor, and a pipe 108 to the tank. In a modification, adapted for quick abandonment of the borehole in the event of a storm, the upper end of the conductor is telescopic and may be lowered below the water at a depth providing safe navigational clearance. Specifications 873,477 and 873,482 are referred to.