GB814520A - Method and apparatus for offshore drilling - Google Patents

Abstract

814,520. Subaqueous boreholes. CALIFORNIA RESEARCH CORPORATION. Nov. 29, 1957 [Dec. 3, 1956], No. 37309/55. Class 85 Subaqueous welldrilling apparatus comprises a rotary table 18 mounted on a platform 20 projecting from a vessel 14 from which a second platform 24 is lowered to the sea-bed at the well site, the platform 24 being secured by casing 26 extending into the earth and being used as a support for the wellh e a d assembly through which ext e n d s drilling apparatus controlled from the vessel. In addition the submerged assembly is provided with means for controlling the opening of the well. Cables 56, 58 passing over sheaves 64, 66 attached to the vessel 14 are used to lower the platform 24, through which the casing 26 extends into a flanged member 28 bolted to the platform, A conduit 34 leading from the casing 26 extends through the member 28 to a valve 36, which is preferably controlled from a distance by a means of leads 38. A preferably flexible conduit 40, e.g. rubber reinforced with steel wire, is connected to the valve so that tanks in surface vessel or land installations can be filled from the well. Secured to the member 28 is a control element 42 to which a flexible guide casing 44, e.g. of steel-reinforced rubber, is detachably clamped. Casing 44 is made in sections joined by flanges 54 and is lowered through the table 18 by a hoist 72. To force the casing 26 into the bed, tubing provided with jet nozzles is lowered through the casing 44 and fluid is pumped through the tubing until the platform 24 rests on the sea-bed. The jet tubing is then withdrawn and further tubing inserted through which cement is lowered to fix the casing 26. When the cement has set, drilling mechanism 74 such as an electric or turbo-drill is lowered down the casing 26 by means of a wire 76 extending through a head 78 sealing the casing 44. When a turbo-drill is used, a flexible hose 80 supplies the motive fluid, drilling mud and cuttings being extracted through a line 82. Initially a reamer is used to drill a hole which will take casing 84, the depth of such drilling depending on the nature of the formations. When the hole is sufficiently deep, the drill is withdrawn, surface casing 84 is lowered into the casing 26 and cemented in place. After the cement sets, the drill is again lowered. A blow-out preventer 86 may be placed at the top of casing 44. To close the well, Fig. 3, cement slurry 88 in a plastic sack 94 within a flexible metal basket is lowered by a wire line 90 into the control element 42, where the metal segments 96 of the basket expand. Drilling mud under pressure is forced on to the slurry, so that when the cement sets the passage through the element 42 is closed. On removing equipment from the top of the guide casing 44 and securing the casing in the table 18, by rotating the table the casing 44 can be detached from element 42. The free ends of wire line 90 and control lines 38 are attached to buoys to indicate the position of the well, the wire line 90 being used as a guide for the flexible casing 44 if the well is reopened. In the arrangement of Fig. 4, the base platform 24 carries a control element 100, which may be one or more valves or one or more blowout preventers. Mounted on the element 100 are control lines 102, a connection 104 for a mud return hose 106 and a drilling head 108. The cables 56, 58 are detachably connected to the platform 24 by an eye 112 secured in a clevis 114 by a pin 116 projecting from a motor 118, which may be hydraulically actuated through a line 120 to withdraw the pin. A swivel head 122 receives a hose 124 supplying fluid to force the casing 26 into the earth. A member 126 in conjunction with the cables 56, 58 serves as a guide for supplying tubing and tools to the well-head and a funnel 110 acts as centring means. The cables 56, 58 after passing over the sheaves may be provided with counterweights.