Patent GB-874178-A (GB)
Title: Apparatus for drilling offshore wells
IPC: E21B43/01
Filed: 1958-04-14
Abstract: 874,178. Boring earth. CALIFORNIA RESEARCH CORPORATION. April 14, 1958 [April 15, 1957], No. 11797/58. Class 85. [Also in Group XXV] An arrangement for subaqueous boring comprises a vessel 10 adapted to be anchored above an underwater well site, well head control equipment 30 operable from the vessel when submerged at the well site, and a flexible conductor 72 adapted to connect to the equipment when submerged at the well site and to extend to the vessel so that a drilling mechanism can be inserted through the flexible conductor and equipment. When the vessel is anchored with the derrick 24 over the site the equipment which comprises a concrete base 36, a length of casing 38, and a fitting 40 is supported in the water by pontoons 32, 34. A branch 132 (Fig. 2) on the casing 38 has a valve 130 operable from the vessel by pressure lines 138, 140, and is connected to a flexible pipe 134 which is secured to a buoy 142 and may be connected to separaters and tanks on a vessel or in a shore installation. A blowout preventer 62 is fixed to the fitting 40 and one end of the conductor is fixed to the preventer whilst the other end passes upwardly through an opening 18 in the vessel to be supported by the derrick. The equipment is lowered to the sea bed at the well site by supplying water to the pontoons through the pipes 112, 114, the weight of the equipment pressing the casing 38 into the sea bed. When the casing will enter the bed no further a string of tubing having jetting nozzles is passed down through the conductor, jetting continuing until the base rests on the bed. The jetting tubing is replaced by cementing tubing and the equipment is cemented to the bed. An electric or turbo drill 148 is lowered through the conductor which is closed by a member 150, the drill being supported from the derrick and the conductor being supported by the derrick or from a platform 20. When a mud driven turbo-drill is used the mud is,urged by a pump 158 through a flexible house 154 which passes over a pulley 154 and is connected to the drill, new sections 162 being added to the hose by a crane 164 as drilling proceeds and a mud line 170 returning the mud through screens 172 to a tank 160. After the hole reaches a length of about 500 ft. casing 174 is cemented into the hole and a cable 100 is tensioned to release the pontoons from the base. Drilling then proceeds, the blow out preventer being operated from the vessel by means of lines 64, 66 if necessary. The completed well is sealed by a mass of cement 176 which is lowered by a wire line 178 having guides 184. After the cement has set the conductor is rotated by a rotary table 22 and raised to disconnect the conductor and blowout preventer from the equipment. Entrance to the well is regained for cleaning by fixing a guide 186 to the conductor, sliding the conductor down the wire line, rotating the conductor to screw its lower end to the fitting, and drilling out the cement. In a modification the pontoons are integral with the underside of the equipment, a releasable fastening operated from the vessel connects the conductor and blowout preventer to the equipment, the upper end of the conductor is connected to rigid casing sliding in a gimbal mounted on the vessel, and the drill is mounted on a string supported by the derrick from a swivel and rotated by a rotary table.