Patent ID: 7457734
Filing Date: 2008-11-25
Classification: E21B,G06F

Abstract:
1. A computer implemented method of evaluating the comparative stabilities of a plurality of drill bits, each of the drill bits comprising a bit diameter, a drilling center, a longitudinal axis through the drilling center, a pin end, a cutting end and an arrangement of cutting elements on the cutting end, for design of a drill bit, comprising the steps of: mathematically displacing each drill bit from its drilling center at a number of angular increments around each bit diameter, calculating a stability index number for each bit at each increment, and displaying values of the stability index for each bit as connected lines at similar angular increments on an orbit diagram; and further comprising the step of calculating a plurality of regenerative forces about the diameter of the drill bit normal to a 1.00 mm displacement of the longitudinal axis of the bit drilling in an earth formation material having an unconfined compressive strength of 11,000 psi; wherein the cutting elements on the cutting end of the designed drill bit are arranged such that the regenerative forces for at least six generally evenly spaced points on the bit diameter have a mean value summed with a standard deviation value totaling less than about 120 lbs force per inch of bit diameter.