Patent GB-839499-A (GB)
Title: Method of drilling from a fully floating platform
IPC: E21B7/128
Filed: 1957-12-20
Abstract: 839,499. Subaqueous well-drilling. CALIFORNIA RESEARCH CORPORATION. Dec 20, 1957 [Dec 21, 1956; Dec. 31, 1956], No. 39656/57. Class 85 Subaqueous boring into steeply sloping formations is carried out from a vessel 10 having a central well 12 through which a drill string 14 is lowered. The drill string 14 comprises a conductor pipe 13 to be cemented in the borehole 15, a drill bit 17, a safety joint 19 and a reduced diameter section 21, so connected by a splined or sliding sleeve 43 that the bit is loaded only by the pipe 13. Drill bit 17 is rotated by a table 39 driven by a motor 41, preferably a rotary hydraulic motor. Surrounding the top of pipe 13 is a flange 45, which may be a four-armed spider or a flat plate and indicates when the pipe has reached the required depth. In drilling for the pipe 13, sea-water may be supplied to the drill-string 14 through hose 51 by a pump 49 from an intake 47. When the pipe 13 enters solid formations, the hole is flushed of debris and cement pumped in by connecting pump 49 through valve 57 to a mixing tank 59. A wiper arm 54 keeps the lower end of pipe 13 clear and cement is cleared from the pipe by dropping a ball 61 through an opening 63. When the ball 61 seats on a cement chaser 65, the pump pressure indicated by a meter 50 rises and the chaser 65 is released from its seat in the coupling ,67 above the joint 19. The chaser 65 clears the lower end of the pipe 13 until stopped by the wiper 54 and prevents back flow of cement into the pipe. When the cement has set, a guide assembly 71 is lowered by cables 73 and includes a bucket element 75, which slides over the joint 19 and lands on the flange 45, where latch members 78 engage a stead engage the flange 45 or the pipe 13 groove in the joint. The latches may in- Shear links 80 breakable by an upward pull on the bucket are provided to free the latches. To keep the cables 73 taut a weight 81 is hung on sheave 83 below the cable drum 76. After the bucket 75 has been latched, the upper part 85 of joint 19 is disconnected and section 21 raised. After the cement has set, ball 61 and the cement at the bottom of the hole is drilled out prior to further drilling of the hole. A well-head assembly 87 is lowered by the guide cables 73, Fig. 5, and comprises gate-type blow-out preventers 89, 91, of which the lower preventer 89 may include a pair of shearing rams by means of which the drill pipe can be cut at the wellhead should need arise. The rams are actuated hydraulically through lines 94, similar lines 93 being provided to control the rams 90, 92 of the blow-out preventer 91. Drilling fluid under pressure supplied by a line 95 can be fed to the well by operating hydraulically a valve 97. An additional blow-out preventer 99 with a control line 100 is provided above the preventer 91 and above this is a drilling head 101 to maintain a seal around the rotating drill pipe and place a back-pressure on drilling fluid returning from the borehole aound the pipe 21 and so force the fluid back to the vessel 110 through the return 103. The back pressure is controlled by packing through a line 104. Guide arms 107, 109 and a funnel 113 are used to place the assembly in position.