岩石内部高压电脉冲等离子体通道生成机理  

Generation mechanism of plasma channels for high-voltage electric pulses in rock

作　　者：刘伟吉[1,2,3] 张有建 罗云旭 祝效华 Liu Weiji;Zhang Youjian;Luo Yunxu;Zhu Xiaohua(School of Mechatronic Engineering,Southwest Petroleum University,Sichuan Chengdu 610500,China;Key Laboratory of Oil and Gas Equipment,Ministry of Education,Sichuan Chengdu 610500,China;Geothermal Energy Research Center,Southwest Petroleum University,Sichuan Chengdu 610500,China)

机构地区：[1]西南石油大学机电工程学院,四川成都610500 [2]石油天然气装备教育部重点实验室,四川成都610500 [3]西南石油大学地热能研究中心,四川成都610500

出　　处：《石油学报》2023年第4期684-697,共14页Acta Petrolei Sinica

基　　金：国家自然科学基金项目(No.52004229,No.52034006,No.52225401,No.52274231);四川省区域创新合作项目(2022YFQ0059);四川省自然科学基金项目(23NSFSC2099);南充市与西南石油大学科技战略合作项目(SXHZ004)资助。

摘　　要：高压电脉冲钻井技术具有破岩效率高、井壁质量好等优点,是一种新型破岩方法。为研究岩石内部孔隙特性对其局部电击穿的影响,构建了多孔隙随机分布的多物理场耦合岩石电击穿二维数值模型,从电路场、电流场、击穿场和温度场耦合的角度实现了多孔隙岩石内部高压电脉冲等离子体通道生成及破岩全过程,主要研究了孔隙特征(即孔隙率、孔径大小和孔隙介质)和电极间距对岩石局部电击穿(即岩石内部等离子体形成)的影响规律。数值研究发现,岩石孔隙对电脉冲破岩效率影响较大,当孔隙内介质为空气时,孔隙发生电击穿,等离子体通道贯穿孔隙;当孔隙内介质为水时,孔隙没有被电击穿,等离子体通道沿着孔隙表面延展;随着孔隙率增大,电脉冲的破岩效果逐渐增强;随着孔隙介质水/气比值减小,等离子体通道生成时间减小,电脉冲破岩的效果逐渐加强;随着电极间距的增大,岩石电击穿时刻逐渐减小,岩石内部“电损伤”区域面积减小。通过开展电击穿破岩的室内实验,再现了电脉冲破岩过程及岩石内部等离子通道形态,电击穿实验结果和仿真试验结果相符合。High-voltage electric pulse(HVEP)drilling technology has become a new rock-breaking method characterized with high rock-breaking efficiency and good borehole wall quality.To study the impact of rock pore characteristics on its partial electric breakdown,this paper establishes a two-dimensional numerical model of multi-physical field coupling electric breakdown with random distribution of multiple pores.Based on this,a whole process of high-voltage electric pulse plasma generation and rock breaking in porous rock is achieved by the coupling of circuit field,current field,breakdown field and temperature field.This paper mainly investigates the law of impact of pore characteristics(i.e.,porosity,pore size and pore medium)and electrode spacing on partial electric breakdown of rock(i.e.,formation of plasma channel in rock).The numerical research indicates that the porosity of rock has a great impact on the rock-breaking efficiency of high-voltage electric pulses.When the medium in pores is air,electric breakdown takes place in pores,and plasma channel runs through the pores.When the medium is water,there is no electric breakdown in pores,and plasma channel extends along pore surface.As the porosity increases,the rock-breaking effect of electric pulses will be gradually enhanced.As the ratio of pore media water to air decreases,the generation time of plasma channel shortens,and the rock-breaking efficiency of high-voltage electric pulses gradually increases.As the electrode spacing enlarges,the electric breakdown time of the rock gradually shortens,and the area of"electric injury"in rock decreases.In addition,a laboratory experiment on rock breaking by electric breakdown is also carried out to reproduce the process of rock breaking by high-voltage electric pulses and the morphology of plasma channels in rock,and it is found that the experimental results of electric breakdown are consistent with the simulation tests.

关 键 词：电脉冲钻井 孔隙岩石 局部电击穿 孔隙流体介质 等离子体通道 

分 类 号：TE21[石油与天然气工程—油气井工程]