GB862828A - Ship positioning means - Google Patents

Abstract

862,828. Oil wells. CALIFORNIA RESEARCH CORPORATION. Dec. 21, 1959 [Dec. 24, 1958], No. 43361/59. Class 85. In off-shore drilling from a floating drilling vessel, the deviations from the vertical of the drill string, or selected lengths of the drill string, is indicated by sensing means which is movable up and down the string, the mooring means of the vessel being adjusted in accordance with the indications. The sensing means comprise a splithalves assembly 50 which is clamped around the drill string 26 and has resilient e.g. synthetic or natural rubber fingers 62, 64 for centering the assembly thereon, and guide tubes 92 through which the lines 34, 36 run. The lines 34, 36 pass around sheaves 44, 46 and are used initially for pulling down the drill string into the well-head 32, a towing-head 48 being attached whilst at the surface, to the lower end of the drill string. A permanent magnet 183 may be attached to the well head to enable the compass orientation of the lower ends of the tow-lines to be ascertained by an instrument run down the drill string, the orientation of the upper ends of the tow lines being determined accordingly. The sensing assembly 50 comprises two chambers 114, 116 each with a pendulum 118, 140 on shafts 120, 142 at right angles, the chambers 114, 116 containing an oscillation-damping fluid. Canting of the assembly 50, due to deviations of the drill string from the vertical, result in displacements of the pendulums, which are transmitted through the shaft 120, 142 to selsyns 134, 148, the conductors 155, 149 from which are combined with a haulage cable 156 which is used for positioning the assembly 50 on the drill string, a balance weight 157 compensating for the one-sided pull. The conductors are connected to recording mechanism 162 through a rotary connector on the winch, the mechanism 162 including a means for indicating the length of cable 156 paid out, and thus the depth of the test. The selsyns 134, 148 are connected through receiving selsyns to amplifiers and the instruments for separately indicating the displacements of the pendulums, the true deviation from vertical being compounded from these readings. Continuous chart readings of the instruments may be obtained, and the compounding may be effected by known means. In a modification, the flexible fingers 62, 64 are replaced by castors having resilient tyres, the pendulums have spring leaf suspensions each having a strain gauge attached thereto to produce an electrical signal in proportion to the degree of bending of the spring. These signals are fed to the amplifiers, and the instruments through balancing bridges which are adjustable to give zero readings when the drill string is vertical. The cable 156 may be guided down a tow-line by a split sleeve 164 to prevent fouling.