GB1156082A - Improvements in Methods for Resharpening Rotary Drill Bits of Composite Type. - Google Patents

Abstract

1,156,082. Resharpening drill bits in situ. BUREAU DE RECHERCHES GEOLOGIQUES ET MINIERES. 7 Feb., 1967 [8 Feb., 1966], No. 5742/67. Heading B3D. A rotary drill bit, e.g. a drill crown 1 comprising abrasive particles such as diamond and a matrix, is resharpened while at the bottom of the bore hole 3, by introducing into the bottom of the bore hole abrasive 4 of a hardness intermediate that of the abrasive particles and the matrix, and moving the drill crown in the abrasive so as to abrade the matrix to increase protrusion of the abrasive particles; the abrasive is then removed by flushing fluid. The abrasive 4 is placed in a container 5 which is lowered into the slightly raised drill string 2 by a cable 6 until it is retained by trigger pins 7. The drill string 2 is then lowered so that the brittle bottom 5a of the container 5 is broken by a push bar, and the abrasive 4 is deposited in the bottom of the bore hole. Instead of using a cable, the container may descent the drill string by gravity or be forced down by the flushing or dilling fluid. The bottom of the container may be of material soluble in the flushing or drill fluid or in a fluid specially injected in to the borehole for this purpose. When used for a full size drill bit 1a the container 5 has a weight 5b to assist breaking of the container. In resharpening a coring tool in situ, the coring tube is used, after removal of the core, to supply the abrasive to the bottom of the bore hole. When drilling with mud, the abrasive may be in a soft plastic container conveyed to the bottom of the hole by the mud, means being provided for bursting or tearing open the container to liberate the abrasive. The resharpening abrasive may be corundum sand, especially when the matrix is steel. If the tool abrasive is tungsten carbide the resharpening abrasive may be quartz sand. Radioactive tracers may be added to the resharpening abrasive so that mud containing abrasive is not stored with the rest of the mud for re-use.