Experiment on the rock-breaking and speed-up mechanism under heavy-duty impact
As the depth of boreholes increases,the traditional mechanical rotary rock-breaking methods have almost achieved their maximum potential for speed enhancement,and so it is increasingly difficult to achieve a substantial acceleration.Impacting rock breaking is one of the most effective mechanical speed-up methods for solving the problems of low rock-breaking efficiency and slow mechanical drilling rate in deep hard formations.Practical applications have demonstrated that impact rock-breaking can increase the speed by 35％-135％,but it still cannot meet the demand of cost reduction and performance enhancement.In view of this,the con-cept of heavy-duty impact rock-breaking is proposed to increase the mechanical energy density of rock-breaking,and its speed-up mechanism and influencing factors are systematically studied through theoretical analysis and laboratory tests.The research findings indicate as follows.(1)The heavy-duty impact method exhibits significant superiority over the traditional rotary cutting,with ROP that is approximately 6 to 8 times faster than the conventional rock-breaking methods.(2)To achieve meaningful speed improve-ments,the impact force of the impactor must exceed the critical energy threshold required for activating internal microcracks,enab-ling crack initiation and connectivity.Increasing the impact force of the impactor represents the most feasible approach to accelerate drilling in deep hard and hot dry rock formations.(3)Since the tensile strength is much smaller than the compressive strength,the compression waves generated by impact is reflected as tensile waves at the free surface.The cumulative effect of these tensile waves results in significant tensile stresses,ultimately leading to tensile breaking.During the impact rock breaking,the rock fragmentation is primarily induced by tensile breaking,with shear breaking as a supplement.
heavy-duty impactrock break with impactdrilling speed-updeep hard formationhot dry rock
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