GB816845A - Well drilling apparatus and method - Google Patents

Abstract

816,845. Automatic cable-tension control systems. MUD CONTROL LABORATORIES Inc. Nov. 26, 1956 [May 14, 1956], No. 36069/56. Class 38 (4). [Also in Groups XXI and XXXVIII] The tension in a cable supporting a well-drilling tool is reduced when it exceeds a pre-determined value in order to maintain the pressure of the tool on the well bottom, by sensing the tension as by passing the cable round a pressure-sensitive ring and releasing the cable reel for a predetermined time when the cable tension exceeds a predetermined value. As shown (Fig. 5), the distortion of the ring moves the slider 76 of a potentiometer 78 in a pre-set bridge circuit, the take-off voltage being applied through smoothing circuits to a D.C. amplifier 194 indicating on meter 196 the deviation in tension from the preset value, and to amplifier 236 and thence to pentode 240 which increase in drill pressure cuts off to operate alarm horn 268 and pneumatic valve 270 which prevents further paying-out of cable. The output of amplifier 236 is also fed to pentode 242 which increase in cable tension causes to conduct, closing switches 280 and 306, and thus bringing into operation multivibrator 282, which operates to close switch 308 and open air valve 318 for a period determined by the setting of resistor 300. The opening of this valve operates a pneumatic cylinder 84 which releases the brake on the cable reel, allowing cable to unwind and reduce cable tension; if cable tension is not reduced sufficiently in this period to open switches 280 and 306 the multivibrator will continue to operate and release the reel for a further period or periods. Potentiometer 168 is pre-set to a position representing the desired tool pressure, and is re-adjusted as further lengths of drill pipe are added since the desired cable tension depends on the total weight of drill and drill pipe less the desired drill pressure.