GB764099A - Improvements in or relating to well drilling assemblies - Google Patents

Abstract

764,099. Boring earth and rock. NAAMLOOZE VENNOOTSCHAP DE BATAAFSCHE PETROLEUM MAATSCHAPPIJ. Sept. 26, 1955 [Dec. 10, 1954], No. 35907/54. Class 85. A rotary well drilling assembly has two or more telescopic hydraulic subs 8, 8' &c. interconnected by collars 10, 10' &c. connected between a drill string and a drill bit 2 for controlling the weight on the bit. Each sub comprises a piston member 3 dividing a cylinder member 4 into upper and lower spaces 5, 6 respectively, the space 5 being in communication with fluid pumped down the drill string to bit nozzles 11 and the space 6 being in communication with the fluid in the borehole and means being provided to prevent relative rotation between the piston 3 and the cylinder 4. In Fig. 1 the drill string has been lifted so taking the weight of the subs 8"', 8", 8' and the cylinder 4, the weight on the bit 2 being due to the pressure difference on the piston 3. This pressure difference may be controlled by varying the rate of circulation of fluid through the drill string. To substantially increase the weight on the bit the drill string is lowered until the piston in the sub 8' moves up in its cylinder when the weight on the bit is the weight of the sub 8, the collar 10 and the pressure difference on the piston in the sub 8', small adjustments in weight being made by adjusting the said pressure difference. The adjustment therefore constitutes a coarse variation by bringing a selected sub into operation and then a fine variation by controlling the pressure difference acting on the piston in said sub. The collars 10, 10' &c. may have different weights. An hydraulic motor may be placed adjacent the bit 2 and a ram device as described in Specification 755,207 may be interposed between the hydraulic motor and the subs. Specification 732,423 also is referred to.