Superabrasive-tipped inserts for earth-boring drill bits

#1. Field of the Invention

#The present invention relates to bits for drilling subterranean formations, and more specifically, to rolling cutter bits (also termed "tri-cone" or "rock" bits) and superabrasive-tipped, insert-type cutting elements for use on the cutters of such bits.

#2. State of the Art

#FIG. 1 is a perspective view of a bit for drilling subterranean formations in accordance with the present invention;

#FIG. 2 is a side partial sectional elevation of a first gage cutting element according to the invention;

#FIG. 3 is a side partial sectional elevation of a second gage cutting element according to the invention;

#Referring to the several views of the drawings, and in particular to FIG. 1, a drill bit according to the present invention is depicted. Bit 11 includes a bit body 13, which includes a threaded shank 15 at its upper end for connection to a drill string, as known in the art. Each leg or section of bit 11 is provided with a lubricant compensator 17, a preferred embodiment of which is disclosed in U.S. Pat. No. 4,276,946 to Millsapps. At least one nozzle 19 is provided in bit body 13 to direct drilling fluid received from the interior of the drill string for cooling and lubrication of the cutting action of bit 11, and removal of material being cut from the formation being drilled. Three cutters, 21, 23 and 25, of generally conical exterior configuration, are each rotatably secured to a bearing shaft associated with and projecting from each leg of bit body 13. Each cutter 21, 23, 25 possesses an exterior cutter shell surface including a gage surface 31 and a heel surface 41.

#A plurality of cutting elements, in the form of stud-like inserts, is arranged in generally circumferential rows extending about each cutter 21, 23, 25. The gage surface 31 of each cutter bears a row of gage cutting elements 33, while a heel surface 41 of each cutter intersecting the gage surface 31 of that cutter bears at least one row of heel cutting elements 43. In certain applications, it is preferred that at least one scraper cutting element 51 is secured to each cutter's shell surface in the general location of the intersection of the gage and heel cutting surfaces, 31 and 41, respectively, intermediate a pair of heel elements 43.

#The outer portion of the cutting structure of each cutter, comprising heel cutting elements 43, gage cutting elements 33, and a secondary cutting structure in the form of at least one scraper cutting element 51, crushes and scrapes formation material at the corner and sidewall of the borehole as cutters 21, 23, 25 roll and slide across the formation material at the borehole bottom as bit 11 rotates under applied torque and WOB. The projecting ends of heel cutting elements 43 effect the primary cutting action, assisted secondarily by scraper cutting elements 51. As the outermost surfaces of heel cutting elements 43 wear, gage cutting elements 33 contact and engage the sidewall of the borehole to maintain gage diameter. Cutting elements 53 arranged in generally circumferential rows radially inward of the rows of heel cutting elements 43 are referred to as inner cutting elements, several rows of such inner cutting elements 53 being located on each cutter 21, 23, 25. Thus, each cutter 21, 23, 25 typically includes a row or ring of gage cutting elements 33, one or more rows or rings of heel cutting elements 43, and one or more rows or rings of inner cutting elements 53.