Patent ID: 7778777
Filing Date: 2010-08-17
Classification: E21B

Abstract:
1. A method for determining bit walk rate of a rotary drill bit comprising: applying a set of drilling conditions to the bit including at least bit rotational speed, rate of penetration along a bit rotational axis, and at least one characteristics of an earth formation; applying a steer rate to the bit; simulating, for a time interval, drilling of the earth formation by the bit under the set of drilling conditions, including calculating a steer force applied to the bit and an associated walk force; calculating a walk rate based on the bit steer rate, the steer force, and the walk force; repeating simulating drilling the earth formation for another time interval, and recalculating the steer force, the walk force and walk rate; repeating the simulating successively for a predefined number of time intervals; calculating an average walk rate of the bit using an average steer force and an average walk force over the simulated time interval; determining respective three dimensional locations of all cutting edges of all cutters and all gauge portions in a hole coordinate system; determining respective interactions of all cutting edges of the cutters and gauge portions with the bottom hole of the formation; calculating a cutting depth for each cutting edge and a cutting area for each cutting element; calculating respective three dimensional forces of the cutters and projecting the forces into a hole coordinate system; summing all of the cutter forces projected in the hole coordinate system; projecting the summed forces into the vertical tilting plane; and calculating the steer force in the vertical tilting plane and perpendicular to bit rotational axis.