DRILLING SYSTEM AND METHOD FOR CONTROLLING THE DIRECTION OF HOLES BEING DRILLED OR CORED IN SUBSURFACE FORMATIONS

摘要

S P E C I F I C A T I O N "A drilling system and method for controlling the direction of holes being drilled or cored in subsurface formations" A steerable rotary drilling system for drilling or coring holes in subsurface formations comprises a bottom hole assembly including a drill bit carrying a plurality of cutting structures, and a mud hammer which applies repeated axial impulses to the bit at a frequency greater than its frequency of rotation. Operation of the mud hammer may be modulated in synchronism with rotation of the drill bit and in controllable phase relation thereto. The drill bit is asymmetrically arranged, for example by an asymmetric distribution of the cutters, so that by appropriate selection of the phase relation the bit may be steered in a desired direction.