Patent GB-856800-A (GB)
Title: Means for offshore drilling
IPC: E21B7/128
Filed: 1959-10-01
Abstract: 856,800. Drilling oil wells. CALIFORNIA RESEARCH CORPORATION. Oct. 1, 1959 [Oct. 1, 1958], No. 33320/59. Class 85. In off-shore drilling, a welltool, e.g., a drill string 26 is pulled down from the floating drilling platform by a towing head 58 by a number, as described two, of tow lines 40, 42 passing around sheaves 82, 84, 92, 94 on a base assembly 38 to winches 44, 46. To begin with, the assembly 38 with a length of conductor casing 36 'is suspended, as shown in dotted lines in Fig. 1, by the lines 40, 42 from the winches 44, 46. A drill string is passed down through the assembly to make a bore to receive the casing 36. The string is retained in the bore whilst the assembly is lowered to land its base plate 60 on the bottom 24, and cementing material is introduced through the string which is then withdrawn. The ends of the towlines have been retained on the vessel and are now attached to the towing head 58 comprising a flotation chamber 112, a central passageway 106 for the tools, a split flange 126 for abutting against a shoulder 120 on the tool part 122, and a cylindrical lower part 128 to which a pair of bails 132, 134 are pivoted on a diametral axis 136. The ends of the lines are attached to the bails so that as the towing head seats with its surface 104 in the flare 76, and ribs 130 on the part 128 located in a cylinder 66, the bails swing aside towards openings 78, 80 in which the sheaves 82, 84 are journalled. The cylinder 66 is secured to the base 60 by latches 70 which engage a groove 72. The latches are held in position by pins 74 which are sheared by heavy upward pulls on the towlines if the well is to be abandoned and the apparatus is to be recovered. A drill string is pulled by the towing head into the base assembly, and a bore is made to receive a length of surface casing 138, the casing 138 being connected by a safety joint 140 to a pipe string which is used for cementing and is then disconnected. The head 58 is now used to pull down a well-head control equipment 182 comprising blow out preventers 144, a "kill" or production-pipe 186 controlled by a remotely operated valve 188, mud return pipe 184 and drilling head 146. A short length of tube 144 is secured to the female part 122 of the safety joint which is within the head 58. When the head is centralized on the base assembly, the control equipment drops until the parts 122 and 140 automatically latch and seal. The control equipment is surmounted by a flared base assembly 158 for a second towing head 174 which is used to introduce tools, e.g., drill string 152 to and through the control equipment to the bore, the string 152 being lowered from the derrick 30 in opposition to a greater pull from the lines 154, which are connected to a pair of bails 176 similar to the bails 132, 134. In a modification, the flare arrangement is inverted, the base plate 60 carrying an upstanding cylinder through which the tools pass, the top of the cylinder contacting with a downward flare on the towing head. The towlines pass around sheaves journalled in brackets projecting radially from the cylinder and are connected to lugs at the rim of the flare.