Secondary cutting structure

摘要

A three cone roller bit with rolling cone cutters that are provided with both primary and secondary cutting elements. The primary cutting elements extend outwardly from lands on the outer surface of the cutter body. The secondary cutting elements are disposed within grooves on the cutter body so as to either protrude with its cutting surface from the bottom of the groove or be flush or slightly recessed within it. During normal operation, the primary cutter elements of the rolling cone cutters engage the borehole formation. The secondary cutters do not engage the formation. After substantial wear has occurred to the primary cutter elements, and wear begins to occur to the body of the cone cutters, the secondary cutter elements serve as a secondary cutting structure that engages and cuts into the formation.