Patent ID: 6095261
Filing Date: 2000-08-01
Classification: E21B

Abstract:
A rotary drilling apparatus, said drilling apparatus comprising:a terminal end of a dual passage drilling string, the terminal end having a central bore, and at least one fluid passageway spaced from the bore and extending downward therethrough;a bit body detachably secured to said terminal end of said drilling string, said bit body having three downwardly extending legs, each leg having a downwardly and generally radially inwardly extending cylindrical journal having an attached end and a free end, said bit body having a central passageway in communication with said central bore for drilling fluid return and a recess defined on an outer surface of said bit body between each of said legs;three roller cutters, one for each leg, each roller cutter comprising a generally conical roller cutter body mounted on the respective leg for rotation about a longitudinal centerline of said journal, each of said roller cutters having a plurality of cutting elements on said roller cutter body; anda shroud affixed to said terminal end and surrounding an upper portion of said bit body, said shroud defining a shroud chamber which communicates with said fluid passageway, said shroud having a lower edge which is closely spaced to said legs of said bit body and which defines fluid ports at each of said recesses for delivery of fluid over the outer surface of said bit body at said recesses.