Research On Bit For Efficient Drilling Of Gas Drainage Borehole In Nantong Mining Area

With the development of economy, energy resources requirement has become increasingly urgent in China. The coal is our country's primary energy. In the course of coal production, the gas always leads to many accidents of safety, which may result in catastrophic consequences. In some mine areas, which drilling technologies are lagging or stratas are complex, the difficuties of drilling lead to a lower gas discharge rate, which seriously influnces the safe production in the mines. So developing or optimizing the efficient and long life bit, appropriate drilling rig and drilling tools, which have great significance in engineering technology and society for the safe and efficient production in coal mine.This paper relies on the projec"Research on the Technique of Increasing Drilling Rate for Gas Drainage Boreholes'Construction in Nantong Mining Co.". Selecting bits by using the optimal division method according to the rock natures and technical conditions of the study area, synthetic diamond impregnated core bit and PDC core bit used in hard rock, three wings centerless PDC bit used in weak and hard rock are determined. The application shows that the layered recommended bits which are good performance in drilling rate and service life, providing a practical method of bits selection. Through analyzing the data at home and abroad, the rock-breaking mechanism and the wearing law of geology PDC and diamond bit are summarized, and the failures of PDC bit are analyzed emphatically.The joint residual stress of PDC/45#steel has been analyzed by thermal elasticplastic of ANSYS( finite element analysis software). The results show that the maximal residual stress is in the contact surface between brazing seam and cemented carbide. The effect of joint shape and the filler metal thickness on the joint were also studied by simulation. At first,the residual stress will decrease with the increase of filler metal thickness, when the thickness is from 100μm to 120μm , the residual stress is the minimum, then the residual stress will be increase with the increasing of thickness. There exists an optimal thickness to the brazing seam. A arc-shaped adge joint is obtained finally, which has a lower residual stress.Crown shape, teeth placement of PDC bit and crown contour, matrix concentration of diamond bit are disigned in this paper. A kind of high performance price ratio PDC is determined for PDC bit manufacture by the optimization experiment. Rig named MK-4, 50mm-drill pipe, 73mm and 58mm-core tube which are produced by Xi'an Branch of China Coal Research Institute are applicated. More than 2000m–drilling experiment is carried out in the study area. Then the month efficiency raises about 80%.