GB948322A - Improvements in the drilling of offshore wells - Google Patents

Abstract

948,322. Drilling and completing subaqueous wells. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. July 28, 1960 [July 30, 1959], No. 26290/60. Heading E1F. An offshore well is drilled and completed with equipment sufficiently beneath the water surface to avoid damage to the equipment by ships. A borehole 32 is drilled from a vessel 11 using a drill string 34 and bits 33, 35. The drill string is guided by a conductor pipe 31 having a wellhead support structure 23, 24 and casing head 36. When a hole has been drilled which is sufficient to receive the pipe it is lowered over the drill string so that the lower end enters the borehole before the end of the drill string leaves it. Guide cables 25, 26, 29 (Fig. 21) are arranged to extend from the wellhead support structure to the vessel, the pipe and structure are lowered until the structure reaches its final position and the pipe is cemented into the borehold by means of a cementing string. A blow-out preventer 56 (Fig. 12) is releasably connected to the casing head, the lower end of a marine conductor 96 is connected to the top of the preventer and the drill string is run through the marine conductor, preventer, and the conductor pipe cemented in the well so that the drilling of the borehole may be continued. After the hole has been drilled to a length sufficient to receive a casing 104 (Fig. 13), the casing is lowered into the well and suspended from a body 105. The casing is cemented in by cement supplied through a string 108 and wiper plug 112 which is finally moved by dropping a ball (not shown) down the string 108 and applying pressure. After the casing has been cemented the string 108, the marine conductor, blow-out preventer and any connections to the structure are withdrawn to the vessel. Two blow-out preventers and a marine conductor are attached to the casing head, and drilling and cementing proceeds for the installation of further casing. After the casing is perforated a single or multiple tubing string is inserted. In the insertion of a dual string (Figs. 17, 28) a guide 194 carrying a tubing hanger 193 and string 192 is first lowered into the well and the second string 196 is then run through the tubing hanger. The marine conductor and the blow-out preventers are removed to the vessel, the tubing strings are raised by means of the guide, the guide is removed and replaced by a complete tubing hanger and a wellhead assembly 207 (Fig. 18) and the tubing hanger and wellhead assembly are lowered and locked to the body 105. The wellhead assembly is closed by a lubricator 206. Specifications 924,904, 948,321, 948,325, 948,330 and 948,331 are referred to.