Abstract: A drilling system for drilling a borehole in an underground formation, comprises a rotary drill bit, a drilling drive mechanism that is capable of applying both rotating the drill bit and applying an axial force to the drill bit, and a control system that is capable of controlling the drive mechanism so as to control rotation of the drill bit and the axial force applied to the drill bit in order to control the depth of cut created by the drill bit when drilling through the formation. A method of drilling a borehole in an underground formation with a rotary drill bit, comprises applying rotation and an axial force to the drill bit and controlling the rotation and axial force so as to control the depth of cut created by the drill bit when drilling through the formation.

Abstract: An expandable drill bit comprises a body for mounting on a support string DS, a plurality of drill arms 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D coupled to the body and extending along a central longitudinal axis LL?, and at least one drill arm supporting cutting elements 6A. The plurality of drill arms 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D are pivotable between a retracted configuration and an expanded configuration. The retracted configuration defines an expandable drill bit having a first cutting diameter D1. The expanded configuration defines an expandable drill bit having a second cutting diameter D2 greater than the first cutting diameter. The drill arms 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D are driven from the retracted configuration into the expanded configuration when the expandable drill bit is rotated at a speed of rotation at least equal to a determined expanding speed of rotation.

Abstract: An expandable drill bit 1 comprises: a body 2 for mounting on a support string DS, a plurality of drill arms 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D coupled to the body 2 and extending along a central longitudinal axis LL?, at least one drill arm supporting cutting elements 6A, and the plurality of drill arms 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D being pivotable between a retracted configuration and an expanded configuration, the retracted configuration defining an expandable drill bit 1 having a first cutting diameter D1, the expanded configuration defining an expandable drill bit 1 having a second cutting diameter D2 greater than the first cutting diameter.