Patent ID: 7546888
Filing Date: 2009-06-16
Classification: E21B

Abstract:
1. A percussion drill bit for drilling into a subterranean earth formation, the drill bit having a central longitudinal axis and being operable by applying repetitive axial percussive impacts on the drill bit in a direction having a component along the axis and by applying rotary motion about the axis relative to the earth formation, the drill bit comprising: a drilling head; one or more axial cutters for predominantly axially cutting the subterranean earth formation in response to the axial percussive impacts; one or more shear cutters for predominantly shear cutting the subterranean earth formation in response to the rotary motion; wherein said axial cutters and said shear cutters are mounted on said drilling head and do not move relative to each other; wherein there is a first shear cutter of the one or more shear cutters, wherein both of said axial and said shear cutters receive percussive impact and wherein one or more of the axial cutters are arranged with respect to at least the first shear cutter to engage the subterranean earth formation earlier during a percussive impact than at least the first shear cutter.