Patent ID: 6123161
Filing Date: 2000-09-26
Classification: E21B

Abstract:
A rotary drill bit for drilling holes in subsurface formations, the bit having a central axis of rotation and comprising a bit body having a shank for connection to a drill string, a plurality of circumferentially spaced blades on the bit body extending outwardly away from said central axis of rotation of the bit, and a plurality of cutters mounted along each blade, at least a majority of which cutters are each located at a different distance from the bit axis than any other cutter, said cutters including primary cutters having cutting edges which define a primary cutting profile and secondary cutters having cutting edges which define a secondary cutting profile which is disposed inwardly of the primary cutting profile with respect to the bit body wherein the primary cutters are mounted on primary blades and at least some of the secondary cutters are mounted on separate secondary blades and there are fewer secondary cutters on each secondary blade than there are primary cutters on each primary blade.