GB849887A - Anchoring systems - Google Patents

Abstract

849,887. Marine structures; drilling oil-wells. CALIFORNIA RESEARCH CORPORATION. June 22, 1959 [June 25, 1958], No. 21323/59. Classes 68(2) and 85. [Also in Group XXXIII] A marine structure, such as an off-shore drilling platform, is anchored by a radiating system of anchor lines of neutral buoyancy, so that they lie in straight lines in the water instead of in catenary curves, the upper ends of the anchor lines being connected to means for maintaining automatically a predetermined maximum tension in the lines. Fig. 2 shows the upper end of a tubular column 24 which has been floated horizontally to the drilling site, up-ended and sunk on to the sea-bed by flooding, and subsequently filling with sand, the bottom compartments. The column 24 accommodates a number of conductor casings 30, for guiding drill strings, the casings 30 being trussed together to form, with shells 34, 36 and longitudinal partitions 38, 40, a rigid column to strengthen the column 24. The anchor lines 64, 66 are arranged in pairs of opposed lines, e.g., three pairs, each line being attached to a bottom anchor consisting of a buoyancy chamber sunk in position by flooding and weighted by filling with sand. The anchor may have projections on its bottom to penetrate into the sea bed. The lines are made of neutral buoyancy by making them of interconnected sections of steel tubing, each section being sealed and properly weighted to be of neutral buoyancy; or a continuous metal tube sealed at its ends and having a wall thickness varying with depth; or a steel cable surrounded with buoyant material; or by buoying a steel cable at intervals. The lines 64, 66 of each pair are trained over pulleys 54, 56, 58, 72, 74 and attached to a single weight 62. The three weights for the three pairs of lines are each of segmental section to lie in circular fashion within the shell 36 longitudinal guides for the weights being provided. A stop 71 limits the fall of the weights if, for example, an anchor creeps. In a modification, the six anchor lines are arranged in two groups of three, each group being attached to a cylindrical weight which is arranged externally around the column. The two weights are of different diameters so that one weight is arranged within the other. The pulleys over which the anchor lines are trained to be attached to the weights are vertically adjustable by winches on the drilling platform. In another modification, the weights are dispensed with, three groups of two lines being attached to the piston rods of three pneumatic cylinders which are kept at the desired pressure by an air compressor and air accumulator. The three cylinders are joined by a common manifold to the air accumulator. Fig. 12 shows a conventional positive buoyancy tied-down drilling structure, the pontoons 158, 160 being kept submerged by lines 162. The anchor lines 166, 180 are arranged in pairs and connected to weights 174 accommodated in guide housings 176.