Study On Rock-breaking Mechanism Of PDC-Diamond Impregnated Matrix Bit For Drilling Hard And Strong Abrasive Formation

At present,the cone bit,PDC drilling bit and diamond bit have been commonly used in drilling strong abrasive hard formations but with not ideal performance.thus a new idea of diamond-impregnated PDC mixed bit was put forward.The new mixed bit adopted PDC cutters as the main cutting component and the impregnated diamond as subsidiary parts,so it combines high rock breaking efficiency of PDC bit and the long working life of diamond bit,providing a new approach to improving the rock breaking speed and working life in drilling strong abrasive hard formations.By the way of carrying experiments and analyzing theoretically,this paper has done research on the combining rock breaking mechanism as well as the main design parameters of the mixed bit.Providing guidance for developing the new type of diamond-impregnated PDC mixed drilling bit.Through analyzing the wear morphology,the corresponding wear mechanism and wear distribution law of worn PDC bits used in igneous rock formations,we can obtain the following conclusions: 1)The main failure modes of PDC cutters in igneous rock formations are abrasive wear and impact damage.The abrasive wear mainly occurs to the cutters on the top of bit crown while the impact damage occurs all around the crown.2)Drawing PDC bit wear distribution curves,we can find that: the cutters on the top of bit crown and in the outer cone are seriously worn and the cutters in the inner cone of bit or near the gauge area are less worn.So diamond impregnated matrix should be placed in the back row of PDC cutters on the top of bit crown in order to prolong the bit working life.Design and fabricate PDC bit,diamond-impregnated matrix bit and diamond-impregnated PDC mixed drilling bit,then carry out laboratory drilling tests to explore how does these different ways of teeth arrangement influence the rock breaking efficiency drilling in granite.The research shows that: 1)For PDC bit,the drilling speed decrease with the increasing wear height of the PDC cutters like a “waterfall”.2)For diamond-impregnated matrix bit,the drilling speed is higher than PDC bit when the wear height of PDC cutter is over 1.5mm.3)By placing the back row of PDC cutters and optimizing relative exposure height between the two rows can increase the efficiency of drilling,but not obvious.4)For diamond-impregnated PDC mixed bit,by placing the back row of diamond impregnated matrix and optimizing relative exposure height,it can still perform high ROP after PDC cutters have been worn.The best relative exposure height between PDC and diamond impregnated matrix is 1-1.5mm in this test.Design and fabricate Ф155.6mm diamond-impregnated PDC mixed drilling bit.The application of the new bit in the deep hard granite formation of horizontal well Jingu 1-1HF in North-East Jinshan gas field indicated better drilling speed and longer drilling life,proving it has very good potential for application.The successful development of the new diamond-impregnated PDC mixed bit could provide new rock crushing tools with high efficiency for drilling abrasive hard formation.