Abstract: A method is provided for removing a body of selected material from the interior of a casing extending into a borehole formed in an earth formation. The method comprises lowering a drill bit for further drilling of the borehole, into the casing, the drill bit having a longitudinal axis of rotation during operation, 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 adapted to remove said selected material from the interior of the casing 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. The drill bit is rotated in the casing, and the control means is operated so as to apply said radially outward force of controlled magnitude to the protection member.

Abstract: A drill bit for drilling a borehole in an object, the drill bit having a central longitudinal axis and comprising: a pilot section for drilling a pilot bore section of the borehole in the object; an under-reaming section in a following position with respect to the pilot section, the cutting diameter Du of the under-reaming section being larger than the cutting diameter Dp of the pilot section; a connecting shaft extending between the pilot section and the under-reaming section; and a stabilising section located between the pilot section and the under-reaming section, wherein the stabilising section fits inside the pilot bore section and is capable of laterally stabilising the drill bit relative to the object while allowing rotation of at least the pilot section relative to the object.

Abstract: A drill bit for drilling a borehole in an object, the drill bit having a central longitudinal axis and comprising: a pilot section for drilling a pilot bore section of the borehole in the object; an under-reaming section in a following position with respect to the pilot section, the cutting diameter Du of the under-reaming section being larger than the cutting diameter Dp of the pilot section; a connecting shaft extending between the pilot section and the under-reaming section; and a stabilising section located between the pilot section and the under-reaming section, wherein the stabilising section fits inside the pilot bore section and is capable of laterally stabilising the drill bit relative to the object while allowing rotation of at least the pilot section relative to the object.