On to Ghent

Abstract

In this study, a new composite impregnated diamond bit was designed to solve the slipping problem when impregnated diamond bit is used for extra-hard, compact, and nonabrasive rock formation. The new bit is composed of sintered diamond-impregnated (SDI) cutters and support body. The support body has weaker resistance to abrasion and would thus wear out faster than SDI cutters during drilling operation. Such design decreases the contact area between the bit work layer and the rock formation and increases the unit load acting on the work layer and the single diamond, thereby improving drilling efficiency. The design parameters and manufacturing technology of the new composite impregnated diamond bit were analyzed to achieve the desired performance. Two Ф41/27 mm laboratorial bits were manufactured to conduct a laboratory drilling test on the rock specimens of fine-grained monzonitic granite rich in biotite. The laboratory drilling test indicated that both the manufacturing technology and the drilling parameters significantly affect the rate of penetration (ROP). The test also indicated that the abrasive resistance of the bit work layer was proportional to the area ratio of SDI cutters to bit bottom face. A very small or very large area ratio in the radial direction causes annular groove or wale at that section, respectively. Therefore, optimization was conducted to coordinate the abrasiveness of the drilled rock formation and abrasive resistance of the bit work layer, and a Ф91.5/71 mm composite impregnated diamond bit was manufactured. The new bit was applied to a hydropower station drilling construction in Fujian Province, China. Field drilling application indicated that the ROP of the new bit was approximately three to four times that of the bits produced by other factories. The ROP relationship was completely similar to the ratio of the applied load acting on a single diamond of the new composite to ordinary impregnated diamond bits.