Method and apparatus for dual speed, dual torque drilling

摘要

A drilling unit for drilling a borehole and having an outer drill bit being rotationally driven by a primary rotary drive mechanism about a primary axis of rotation and having an outer bit cutting face disposed for drilling engagement with formation material. The outer drill bit defines an inner bit passage intersecting the outer bit cutting face. An inner drill bit is rotationally driven within the inner bit passage by a secondary rotary drive mechanism and has a secondary axis of rotation that can be the same or can be laterally offset from the primary axis of rotation. An inner bit cutting face is defined by the inner drill bit and is located within the inner bit passage. Rotation of the outer drill bit for borehole drilling causes orbital rotation of the inner drill bit about the primary axis of rotation simultaneously with rotation of the inner drill bit about the secondary axis of rotation for continuously cutting away formation material at the central region of the borehole being drilled.

主权项

1. A method for drilling boreholes in earth formations, comprising:
rotating an outer drill bit with a primary power source about a primary axis of rotation and against an earth formation, the outer drill bit having an outer bit cutting face in cutting engagement with the earth formation and defining an inner bit chamber intersecting said outer bit cutting face and defining an inner bit chamber opening at said outer bit cutting face; with a secondary power source independently rotating an inner drill bit having an inner bit cutting face within said inner bit chamber with said inner bit cutting face located within said inner bit chamber opening and having formation cutting engagement with the formation simultaneously with said rotating said outer drill bit in cutting engagement with the formation; said rotating said inner drill bit being rotating said inner drill bit within said inner bit chamber about an axis of rotation that is laterally offset from said primary axis of rotation and developing an orbital pattern of formation cutting motion of said inner drill bit in cutting engagement with the formation about said primary axis of rotation responsive to rotation of said outer drill bit; and rotating said inner drill bit with said secondary power source independently of rotation of said outer drill bit and simultaneously with rotation of said outer drill bit with said primary power source.