GB755207A - Improvements in or relating to well drilling systems and methods of operating such systems - Google Patents

Abstract

755,207. Boring earth and rock. NAAMLOOZE VENNOOTSCHAP DE BATAAFCHE PETROLEUM MAATSCHAPIJ. Sept. 26, 1955 [Dec. 10, 1954], No. 35904/54. Class 85 Well drilling aparatus comprising a drill bit with flushing fluid nozzles, a motor for rotating said bit, and a tubular drill string, wherein the connection between the bit and the drill string includes a ram device comprising two hollow telescopic members for controlling the weight on the bit when the conditions under which the bit is advancing vary. The motor may be at the top of the borehole or it may be adjacent the bit when the drill string is kept stationary or rotated very slowly. In one embodiment, Fig. 1, the outer telescopic member 3 of the ram is secured to the bottom of the drill string 1 and the inner member 4 carries the bit 2. The two members 3, 4 are splined together at 5 to allow relative axial movement only. The outer member 3 has abutments 8 defining separate cylinders and the inner member 4 has pistons 6 dividing each cylinder into upper and lower cylinder spaces 7. The spaces 7 above the pistons 6 are subject via passages 11 to the pressure of the drilling mud passing down the drill string to nozzles 10 in the bit 2 while the cylinder spaces 7 below the pistons 6 are subject, via passages, 12 to the pressure of the drilling mud in the borehole, the pressure difference between the upper and lower spaces 7 acting downwards on the bit. The bit may have relief valves to limit the pressure difference across the nozzles 10. In another embodiment. Fig 9B, the motor is a hydraulic turbine driven by the drilling mud and is placed adjacent the bit, a shaft 21 from the turbine driving a gear pump 22<SP>1</SP> which supplies drilling mud or a separate servo fluid under pressure through a pipe 24 and passages 25 to the spaces 7 above the pistons 6, the fluid passing through venting orifices in the pistons to the spaces 7 below the pistons from where it returns to the pump through passages 12<SP>1</SP> and a pipe 24<SP>1</SP>. One or more of the pistons 6 may be put out of action to reduce the weight on the bit by connecting the spaces 7 above and below the piston either together or to equal pressure sources. This can be performed manually by removing, replacing or adjusting screwthreaded plugs in the abutments 8 or in the walls of the members 3, and 4 or performed automatically by spring-loaded valves which render a piston 6 inoperate when the pressure difference above and below it exceeds a predetermined value or when the rate of circulation of the drilling mud exceeds a predetermined value. In this way the pistons, which may have different surface areas, may be put out of action one at a time, and the weight on the bit, together with the speed of the turbine (if used), can be controlled by the pressure or the rate of circulation ,of the drilling mud in the drill string.