Abstract: A reamer for drilling a hole having a diameter larger than a pass through diameter in one aspect includes a body having reaming blades affixed at azimuthally spaced apart locations. These blades have cutters attached at selected positions. An outermost surface of each blade conforms to a radially least extensive one, from a longitudinal axis of the reamer, of a pass through and a drill circle, The drill circle is substantially coaxial with the axis. The pass-through circle is axially offset from the drill circle and defines a section wherein the pass-through circle extends from the axis past the drill circle, so that cutters disposed on the reaming blades in the section drill at full drill diameter, while avoiding wall contact at the pass-through diameter. In another aspect, the reamer includes a pilot hole conditioning section including azimuthally spaced apart blades affixed to the body longitudinally ahead of the reaming blades.

Abstract: A method is disclosed for drilling a wellbore. The method includes operating a turbine-type mud motor having a bi-center drill bit coupled to it, and applying an axial force to the bit which is selected so that the bit drills in a directionally stable manner. In one embodiment, the motor is a steerable motor operated to maintain a selected trajectory of the wellbore.

Abstract: A bi-center drill bit includes pilot and reaming blades affixed to a body at azimuthally spaced locations. The blades have PDC cutters attached at selected positions. In one aspect, the pilot blades form a section having length along the bit axis less than about 80 percent of a diameter of the section. In another aspect, selected pilot blades and corresponding reaming blades are formed into single spiral structures. In another aspect, shapes and positions of the blades and inserts are selected so that lateral forces exerted by the reaming and the pilot sections are balanced as a single structure. Lateral forces are preferably balanced to within 10 percent of the total axial force on the bit. In another aspect, the center of mass of the bit is located less than about 2.5 percent of the diameter of the bit from the axis of rotation. In another aspect, jets are disposed in the reaming section oriented so that their axes are within about 30 degrees of normal to the axis of the bit.

Abstract: A bi-center drill bit includes pilot and reaming blades affixed to a body at azimuthally spaced locations. The blades have PDC cutters attached at selected positions. In one aspect, the pilot blades form a section having length along the bit axis less than about 80 percent of a diameter of the section. In another aspect, selected pilot blades and corresponding reaming blades are formed into single spiral structures. In another aspect, shapes and positions of the blades and inserts are selected so that lateral forces exerted by the reaming and the pilot sections are balanced as a single structure. Lateral forces are preferably balanced to within 10 percent of the total axial force on the bit. In another aspect, the center of mass of the bit is located less than about 2.5 percent of the diameter of the bit from the axis of rotation. In another aspect, jets are disposed in the reaming section oriented so that their axes are within about 30 degrees of normal to the axis of the bit.

Abstract: A PDC bit for cutting a hole below a point in a formation, the diameter of the hole being greater than the diameter of the hole above the point, comprising: a bit body having an axis of rotation, a first cutting portion having a first radial extent from the axis of rotation, a second cutting portion that is not axially spaced apart from the first cutting portion and that has a second radial extent that is greater than said first radial extent, wherein the total imbalance forces resulting from engagement of said first and said second cutting portions with the formation are balanced such that the resulting torque on the bit is minimized and in particular, the component of the torque on the bit about an axis normal to the axis of rotation is minimized. In some embodiments, the bit has a central recessed portion on its face, which receives a short "core" portion that enhances stabilization of the bit.

Abstract: A rotary drill bit comprises a bit body having a leading surface formed at least in part from solid infiltrated matrix material, a major part of the leading surface being impregnated with abrasive particles of diamond or other superhard material. There are also mounted at the leading surface a plurality of larger cutting elements having cutting edges formed of superhard material which project above the surface, the larger cutting elements being so spaced as to define a substantially continuous cutting profile, so that the cutting elements in combination sweep over the whole of a bottom of a hole being drilled by the bit, during each revolution. The abrasive particles normally carry out the majority of the drilling action in hard formations, but the larger cutting elements serve to cut more rapidly through temporary obstructions which may be encountered in the borehole, such as a shoetrack.

Abstract: A rotary drill bit for drilling subsurface formations comprises a bit body having a shank for connection to a drill string, a plurality of primary blades and at least one secondary blade circumferentially spaced and extending outwardly away from a central axis of rotation of the bit, a plurality of cutters mounted along each blade, a majority of the cutters mounted on each of the primary blades having a greater exposure than a majority of the cutters on the secondary blade, and a sweep angle of the secondary blade is less than a sweep angle of the primary blades. The drill bit will exhibit a rate-of-penetration as a function of the size of the cutters on the primary blades, and exhibit a torque profile as a function of the size of the cutters on the at least one secondary blade.