GB873477A - Improvements in or relating to off-shore drilling or like underwater operations - Google Patents

Abstract

873,477. Boreholes. SHELL OIL CO., CONTINENTAL OIL CO., SUPERIOR OIL CO., and UNION OIL CO. OF CALIFORNIA. Aug. 14, 1957, No. 25608/57. Class 85. [Also in Groups XXVI and XXXIV] Subaqueous apparatus for drilling or working in a borehole 24 comprises a floating vessel 20, a well-head base anchored over the borehole in a formation 23, laterally flexible guides 61 between the base and vessel, means for lowering the drilling or working tool from the vessel, and means for slidably connecting the tool and the guides so that as the tool is lowered it is constrained to register with the upper end of the borehole, Mounted on the vessel are a mud tank 51, a draw-works 25, a collapsible drilling rig 27, and a rotary table 36 mounted on gimbals over a collar 39. A length of casing 45 fixed in the borehole is secured to a pair of arms 58 resting on the formation. A circulating head 43 is releasably sealed to a receiver 44 which is releasably sealed to the casing. A guide post 60 extends from each arm 58, a guide line 61 extending from the bottom of each post out through the top, and a sleeve 63 connected to the head engaging each post. During the installation of the head it is first supported within the collar with the guide lines threaded through the sleeves and running over pulleys 69, 66. A drill collar 46 is lowered through the head, the bit 47 is secured to the collar, and the head is released, the bit engaging an internal shoulder within the head to support it. The head is lowered on to the receiver by adding drill pipe sections to the collar and is finally sealed to the receiver. With the bit slightly off the bottom of the borehole the pipe is rotated to give it a bow which will compensate for up and down movements of the vessel. Whilst the pipe is still rotating it is lowered until the bit begins to cut, a constant force being applied to the bit. During drilling, mud is supplied from the tank, down the drill pipe to the bit and is returned up the space between the pipe and the hole to the head from whence it passes through a drilling mud return line 55 to the tank. The drill pipe is withdrawn from the well by releasing the head from the receiver and hoisting the pipe, the bit engaging the shoulder within the head so that it is also hoisted. If drilling is to be discontinued in the event of a storm, a length of drill pipe slightly greater than the depth of the water is removed from the string, the remaining string is plugged by a tool affording a landing seat, and the remaining string is lowered until the tool seats on the circulating head. A well is completed by running the Xmas tree into the casing using the guide lines, sealing the tree to the casing, and connecting flexible hoses attached to the tree to the shore or a tanker. In the embodiment shown in Figs. 2 and 3 the arms 58 are connected to a sleeve 94 surrounding casing 92 which is screwed at its upper end to receiver 106 which also rests on an internal ring welded to the sleeve 94. The receiver has a slot 112 which facilitates raising and lowering of the casing and removal of the receiver from the casing. The circulating head has a sealing ring 117 which is contracted by hydraulic pressure to engage a groove 111 in the receiver. The drill pipe is resiliently gripped by a seal 190 rotatably mounted in the upper part of the head, the bearing supporting the seal being lubricated with water supplied through a port 151. A nipple 132 serves as the connection to a drilling mud return line. Specifications 873,479 and 873,481 are referred to.