Patent ID: 8387725
Filing Date: 2013-03-05
Classification: E21B

Abstract:
1. An air-cooled hammer bit for drilling a borehole in earthen formations, the bit comprising: a bit body having a bit axis and a bit face with an outermost radius, wherein the bit face includes an inner region extending from the bit axis to about 50% of the bit radius and an outer region extending from the inner region to the outermost radius; a plurality of gage cutter elements mounted to the bit face in a circumferential gage row in the outer region, wherein the circumferential gage row extends around the bit axis and wherein each gage cutter element in the gage row is disposed at the same radial position relative to the bit axis; a plurality of adjacent to gage cutter elements mounted to the bit face in a circumferential adjacent to gage row in the outer region, wherein the circumferential adjacent to gage row extends around the bit axis and wherein each adjacent to gage cutter element is disposed at the same radial position relative to the bit axis; and a plurality of inner row cutter elements mounted in a plurality of circumferential rows in the inner region and the outer region, wherein each circumferential row of inner row cutter elements extends around the bit axis and wherein each inner row cutter element is radially positioned between the bit axis and the adjacent to gage cutter elements; wherein each cutter element has a cutting portion extending from the bit face, the cutting portion defining a cutting profile in rotated profile view; wherein the cutting profile of at least one gage cutter element in the gage row in the outer region radially overlaps with the cutting profile of at least one adjacent to gage cutter element in the adjacent to gage row in rotated profile view, wherein the cutting profile of each cutter element in the outer region radially overlaps with the cutting profile of at least one other cutter element in a different row; wherein a radial distance between an inner radius of the cutting profile of each gage cutter element and an outer radius of the cutting profile of each adjacent to gage cutter element defines a radial overlap distance, and wherein each gage cutter element and each adjacent to gage cutter element has a diameter, wherein the ratio of the radial overlap distance to the diameter of the gage cutter element is between 0.10 and 0.60; wherein the cutting portion of each gage cutter element extends radially from an inner radius measured perpendicularly from the bit axis to an outer radius measured perpendicularly from the bit axis, wherein the cutting portion of each adjacent to gage cutter element extends radially from an inner radius measured perpendicularly from the bit axis to an outer radius measured perpendicularly from the bit axis; wherein the inner radius of the cutting portion of each gage cutter element is less than the outer radius of the cutting portion of each adjacent to gage cutter element; wherein the radial distance between the inner radius of the cutting profile of each adjacent to gage cutter element and the outer radius of the cutting profile of each gage cutter element defines a radial span distance; and wherein the ratio of the radial overlap distance to the radial span distance is between 0.10 and 0.50.