Directional drift and drill PDC drill bit

A drill bit for drilling a hole in a formation having a diameter greater than a diameter of an opening through which the drill bit can pass, the drill bit comprising:

• a bit body having an axis of rotation;
• a plurality of blades azimuthally spaced apart on one end of the body at substantially the same axial position along the axis of rotation, wherein at least one of the blades has a greater radial extent from the axis of rotation than the other blades, the blades defining a cutting surface having a geometric axis laterally offset from the axis of rotation;
• and
• a plurality of cutter elements attached to the blades at selected positions so that lateral forces exerted by the cutter elements on the blades substantially balance.

A bi-centered drill bit, comprising:

• a bit body having an axis of rotation;
• a cutting surface on one end of the bit body having a geometric axis laterally offset from the axis of rotation, the cutting surface comprising a plurality of blades arranged at azimuthally spaced apart locations at substantially the same axial position, wherein at least one of the blades has a greater radial extent from the axis of rotation than the other blades;
• a plurality of cutter elements spaced apart and affixed to the blades at selected positions along each blade;
• and
• a bit profile along the blades defined by a single curved portion and an adjacent linear gage portion, wherein an angle between a line perpendicular to the profile and the axis of rotation of the bit body generally increases continuously from zero or negative for an inner point along the profile to approximately 90.degree. for an outer point along the profile.