Patent ID: 8176999

Claim:
A steerable drill bit arrangement comprising a drill bit, a steering component and a stabilizer, the steering component being adapted to provide a steering force which in use can drive the drill bit along a non-linear path, the stabilizer being located between the drill bit and the steering component, the stabilizer having a tubular body with a longitudinal axis and a number of blades projecting radially outward from a tubular body, each of the blades providing a bearing surface which lies radially outward of the tubular body, the whole of the bearing surface being adapted to engage a non-linear borehole during use whereby the bearing surfaces of the blades of the stabilizer provides a fulcrum for the steering force provided by the steering component, the bearing surface of each blade comprising five sections at different longitudinal positions: a central section which is not tapered; two end sections, an end section being located at each end of the blades, the end sections having a first taper; and two intermediate sections, an intermediate section being located between the central section and each of the end sections, the intermediate sections having a second taper, the angle of the first taper relative to the longitudinal axis being greater than the angle of the second taper relative to that axis, the radial distance between the end sections of the bearing surface and the tubular body being bridged by further tapered surfaces which do not form part of the bearing surface.