Abstract: A top mount dual bit well drilling mechanism has a rotary driven tubular housing having a top mount body within an upper end portion of the housing to which the upper end of a mud motor is mounted for support within the housing. A reamer bit is connected for rotation by the tubular housing upon rotation by a well drilling string and defines a core removing bit chamber that is recessed within the reamer bit and has communication with the core receiving receptacle. A core removing bit is rotated within the core removal bit chamber by the mud motor and continuously cuts away the upper end of a formation core that enters the receptacle as the reamer bit cuts into the formation.

Abstract: A steerable dual drilling bit having an outer reamer bit defining a central opening and having an inner core removal bit being rotatably driven by a mud motor that is supported within a tubular housing by the outer reamer bit. The dual drilling bit is capable of being threaded to the bit box of a rotary drill string or a straight or bent housing drilling system. The dual drilling mechanism is of sufficiently limited length that it is capable is being efficiently steered for directional drilling. The reamer and core removal bits are arranged to continuously cut away a formation core and to employ the core for rotational stabilization of the reamer bit during drilling.

Abstract: 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.

Abstract: 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.