CO2 drilling is a promising underbalance drilling technology with great advantages,such as lower cutting force,intense cooling and excellent lubrication.However,in the underbalance drilling,the mechanism of the coupling CO2 jet and polycrystalline-diamond-compact(PDC)cutter are still unclear.Whereby,we established a coupled smoothed particle hydrodynamics/finite element method(SPH/FEM)model to sim-ulate the composite rock-breaking of high-pressure CO2 jet&PDC cutter.Combined with the experimen-tal research results,the mechanism of composite rock-breaking is studied from the perspectives of rock stress field,cutting force and jet field.The results show that the composite rock-breaking can effectively relieve the influence of vibration and shock on PDC cutter.Meanwhile,the high-pressure CO2 jet has a positive effect on carrying rock debris,which can effectively reduce the temperature rising and the ther-mal wear of the PDC cutter.In addition,the effects of CO2 jet parameters on composite rock-breaking were studied,such as jet impact velocity,nozzle diameter,jet injection angle and impact distance.The studies show that when the impact velocity of the CO2 jet is greater than 250 m/s,the CO2 jet could quickly break the rock.It is found that the optimal range of nozzle diameter is 1.5-2.5 mm,the best injec-tion angle of CO2 jet is 60°,the optimal impact distance is 10 times the nozzle diameter.The above studies could provide theoretical supports and technical guidance for composite rock-breaking,which is useful for the CO2 underbalance drilling and drill bit design.

Can Cai;Pei Zhang;Daping Xu;Xianpeng Yang;Yingfang Zhou

School of Mechanical Engineering,Southwest Petroleum University,Chengdu 610500,China;Key Laboratory of Groundwater Resources and Environment,Jilin University,Ministry of Education,Changchun 130021,China;Laboratory of High-pressure Jet Theory and Application Technology,Southwest Petroleum University,Chengdu 610599,China;School of Engineering,University of Aberdeen,Aberdeen AB24 3FX,United Kingdom;School of Intelligent Manufacturing,Panzhihua University,Panzhihua 617000,China

矿业科学技术学报（英文版）

[1]Can Cai;Pei Zhang;Daping Xu;Xianpeng Yang;Yingfang Zhou-.Composite rock-breaking of high-pressure CO2 jet&polycrystalline-diamond-compact(PDC)cutter using a coupled SPH/FEM model)[J].矿业科学技术学报（英文版）,2022(05):1115-1124

underbalance,Whereby

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