Patent ID: 7467671

Claim:
A drill bit for drilling a borehole into an earth formation, the drill bit being adapted to remove a body of selected material from the interior of a casing extending into the borehole, whereby during operation the drill bit has a longitudinal axis of rotation, the drill bit comprising rock cutting means, at least one protection member for protecting the inner surface of the casing from contact with the rock cutting means, each protection member being sufficiently wear-resistant to effectively clean the casing of said selected material but of lower hardness than said rock cutting means and being radially movable towards the inner surface of the casing, and control means for applying a radially outward force of controlled magnitude to the protection member; wherein the drill bit further comprises a reamer arm movable in a radial direction relative to said axis of rotation, wherein the rock cutting means and each protection member are provided at the reamer arm; wherein the control means is arranged to move the reamer arm in radial direction relative to said axis of rotation; and wherein the reamer arm is provided with gauge protection means for protecting the reamer arm against wear during further drilling of the borehole with the drill bit, and wherein the protection member is arranged on top of the gauge protection means at the radially outward side thereof.