Reaming apparatus and method with enhanced stability and transition from pilot hole to enlarged bore diameter

摘要

A method and apparatus for reaming or enlarging a borehole with enhanced stability. A pilot stabilization pad (PSP) having an axially and circumferentially tapered entry surface and a circumferential transition surface thereabove is employed to enhance the transition from the smaller diameter borehole to be enlarged while accommodating the side force vector generated by the cutting assembly used to effect the enlargement. In addition, one or more eccentric stabilizers are employed above the reaming apparatus to laterally or radially stabilize the bottomhole assembly, which may comprise either a straight-hole or steerable, motor- driven assembly.