GB857173A - Bit weight applicator - Google Patents

Abstract

857,173. Borehole apparatus. JERSEY PRODUCTION RESEARCH CO. April 16, 1959 [May 14, 1958], No. 13047/59. Class 85. An hydraulically operated device for applying cutting pressure to a drill-bit comprises a piston assembly connected to the drill-bit and a cylinder with expanding wall-sections which can be locked in the well-casing. The piston assembly-which forms the upper part of the device and is shown in Fig. 1A is formed by an inner mandrel 10 which is supported by a drill string 12, and which enters a cylinder 46 through a bearing 26 and a packing gland 28, and a piston 38 which is secured to the mandrel and slides in the cylinder 46. A port 49 in the wall of the mandrel connects the cylinder with the bore of the mandrel. A second piston 60 is attached to the mandrel at a lower point and runs in a cylinder 62 which is connected with the mandrel bore by a port 72. The intermediate part of the device (Fig. 1B) comprises individual rubber anchor blocks 64 moulded around a metal core which can be expanded by internal pressure so that the blocks grip the well casing, there are longitudinal passages between the individual blocks to permit circulation of the drilling fluid. In operation the device is lowered into a bore and drilling fluid is pumped down the drill-string to expand the anchor blocks and subsequently act on the pistons 38 and 60 to apply pressure to the drill bit. An automatic bottom device 93 (Fig. 1c) which ensures that the anchor blocks lock before the mandrel is allowed to move longitudinally of the cylinder comprises buttress-threaded segments 94 which engage a similiar thread on the mandrel 10. The mandrel can only be released from the segments by right-hand rotation which screws the mandrel out of the segments, but since they are spring-loaded the mandrel can be re-engaged with the segments by an upward movement of the drill-string.