Cutting structure for roller cone drill bits

#1. Technical Field

#The invention relates generally to roller cone drill bits for drilling earth formations, and more specifically to roller cone drill bit designs.

#2. Background Art

#FIG. 1 shows a schematic diagram of a drilling system for drilling earth formations.

#FIG. 2 shows a perspective view of a prior art roller cone drill bit.

#FIG. 3A is a diagram of the roller cones of a prior art drill bit illustrating the intermeshing relationship of the cutting elements between the cones.

#Referring to FIGS. 4-7, in one embodiment, the invention comprises a roller cone drill bit which includes a bit body 200 (partial view in FIG. 5) and a plurality of roller cones (typically three), shown generally at 210 in FIG. 4. The roller cones 210 are attached to the bit body 200 and rotatable with respect to the bit body 200. In this embodiment, the cones 210 include a first cone 214, a second cone 216, and a third cone 218. Each cone 214, 216, 218 includes an exterior surface, generally conical in shape, having a side surface 250. Disposed about the side surface 250 of each cone 210 is a plurality of cutting elements, shown generally at 212 and additionally at 256. A distinction between cutting elements 212 and cutting elements 256 will be further explained.

#The plurality of cutting elements disposed on each cone are arranged primarily on the side surface 250 of each cone 214, 216, 218, as shown in FIG. 4. In general terms, at least three different types of cutting elements may be disposed on the cones, including primary cutting elements, generally indicated as 212, gage cutting elements, generally indicated as 256 and ridge cutting elements (not shown). In the embodiment of FIG. 4, primary cutting elements 212 are the cutting elements generally arranged about the side surface 250 of the cones and used as the primary means for cutting through the bottomhole surface of the earth formation. Primary cutting elements 212 are arranged on each cone such that cutting elements on adjacent cones intermesh between the cones. Gage cutting elements 256 are cutting elements which scrape the wall of the well bore to maintain the diameter of the well bore. Gage cutting elements 256 are typically arranged in one or more rows, often referred to as “gage” rows, “heel” rows, or “trucut” rows, about the lower edge of one or more cones as shown at 256 in FIGS. 4, 5, and 7. Ridge cutting elements (not shown) are miniature cutting elements, typically comprising hardened material deposits, that are optionally disposed about the surface of the cone, usually between primary cutting elements 212 to cut ridges of formation which pass between primary cutting elements 212 on the cones. Ridge cutting elements (not shown) are used to reduce damage or wear of the cone surface by reducing contact between the cone surface and the formation ridges.

#It should be understood that in a drill bit according to the invention, the cutting elements may comprise only primary cutting elements 212, or primary cutting elements 212, gage cutting elements 256 and, optionally, ridge cutting elements (not shown). Further, while primary cutting elements 212 and gage cutting elements 256 are shown as distinctly different sets of cutting elements in this embodiment, it should be understood that in other embodiments, one or more primary cutting elements 212 may be disposed on one or more cones to essentially perform as a gage cutting element. The types and combinations of cutting elements used in specific embodiments of the invention are matters of choice for the bit designer and are not intended as limitations on the invention. Further, it should be understood that all cutting elements between adjacent cones may not necessarily intermesh. The number of cutting elements and the arrangement of cutting elements that intermesh between adjacent cones are also matters of choice for the bit designer.