Systems and methods for determining and/or using estimate of drilling efficiency

A method for estimating a parameter related to drill bit wear during a subterranean drilling operation, the method comprising:

• (a) rotating a drill bit in a wellbore to drill into a subterranean formation, the drill bit having an unknown bit wear;
• (b) measuring a set of corresponding weight on bit (WOB) and torque on bit (TOB) values while rotating in (a), the set measured when WOB and TOB values ramp up from lower values after a pause in drilling or ramp down from higher values as drilling pauses, said measurements made at a frequency of at least 1 Hz during said ramp up or ramp down;
• (c) fitting a nonlinear curve to a cross plot of the measured set of WOB and TOB values, the cross plot having TOB on the ordinate and WOB on the abscissa;
• (d) evaluating the nonlinear curve to obtain the parameter related to drill bit wear, said evaluating including locating a steady state point in the nonlinear curve above which the curve is substantially linear, wherein the parameter related to drill bit wear is equal to a WOB value at the steady state point and is a product of a rock strength ε of the subterranean formation and an area of a wear flat Aw, on the drill bit, the area of the wear flat being indicative of the drill bit wear;
• (e) resuming drilling using a weight on bit above the WOB value at the steady state point;
• (f) measuring a rate of penetration of drilling (ROP), a rotation rate of the drill bit (RPM), the TOB, and the WOB while drilling in (e);
• (g) processing the ROP and the RPM measured in (f) and the parameter related to drill bit wear obtained in (d) to compute a modeled WOB and a modeled TOB at a plurality of estimated values of the area of the wear flat;
• and
• (h) comparing the modeled WOB and the modeled TOB computed in (g) and the WOB and TOB measured in (f) at each of the values of the area of the wear flat to determine a likelihood of each area of the wear flat being correct.