Patent ID: 8274399

Claim:
A computer implemented method to use in a drilling system having multiple cutting structures, including a bit and one or more secondary cutting structures, to balance the rate of penetration of the drilling system and the wear on the cutting structures by controlling weight on bit and RPM, the method comprising: (O1) calculating a predicted rate of penetration for the bit, using in the calculation the current predicted wear on the bit and the properties of the rock to be penetrated by the bit; (O2) calculating a predicted rate of penetration for at least one of the one or more secondary cutting structures, using in the calculation the current predicted wear on the secondary cutting structure and the properties of the rock to be penetrated by the secondary cutting structure; (O3) determining the slowest rate of penetration among those calculated for the bit and at least one the one or more secondary cutting structures; (O4) calculating the weight on bit and RPM for each of the bit and at least one of the one or more secondary cutting structures to substantially match the determined slowest rate of penetration; and (O5) summing the calculated weights on bit to calculate a goal weight on bit for the drilling system and setting a goal RPM for a rotary portion of the drilling system to the slowest RPM calculated for the cutting structures that rotate at substantially the speed of the rotary portion of the drilling system.