Research On The Mechanism Of Rock Breaking By Electrohydraulic Effect

How to improve rock breaking efficiency in deep wells and ultra-deep wells is one of the critical challenges facing the efficient development of deep oil and gas resources due to the high hardness and abrasive nature of deep formation rocks.The rockbreaking method based on electrohydraulic effect is a new type of efficient rockbreaking method that converts electrical energy into mechanical energy,and there is little research on its rock-breaking mechanism and rock-breaking rules by researchers.In this thesis,we have systematically researched the mechanism and rules of rockbreaking electrohydraulic plasma by applying indoor experiments,theoretical analysis,and numerical simulation,and the main results are as follows.A rock-breaking experimental setup was developed independently,consisting of a high-voltage pulse power supply,a reactor,and a measurement system.Based on the pulse power theory,the charging and discharging process of the high-voltage pulse circuit was simulated by Multism simulation software,and the variation rules of the discharge parameters with the parameters of the circuit components were obtained,and then the optimized design of the high-voltage pulse power supply was carried out.The rock-breaking reactor was optimized according to the characteristics of the electrohydraulic plasma rock-breaking process,so that the discharge electrodes,liquid,and rock could be reasonably arranged.Based on the data measurement requirements,a measurement system that can monitor the discharge voltage and current,underwater shock wave pressures,and rock damage was built.Based on the microbubble electric breakdown theory,the high voltage pulse discharge process in liquid was studied,and the microscopic mechanism of electric breakdown formation and the expansion and compression of plasma channel were analyzed to reveal the causes of shock wave.Based on the improved calculation method of non-ideal plasma conductivity and the energy conversion during the discharge process,the response law of the plasma channel in the discharge loop,and the mechanical behavior of the channel,a shock pressure model of the electrohydraulic plasma shock wave was established and verified by indoor experiments data.The influence of breakdown voltage,capacitance,discharge loop resistance,and discharge loop inductance on the shock wave pressure were further analyzed to provide a theoretical basis for optimizing the shock wave strength and energy efficiency.According to the above research results,experiments of electrohydraulic plasma rock-breaking were conducted to explore the influence of discharge parameters(discharge voltage and the number of discharges),liquid properties(electrical conductivity),and rock types(sandstone,granite,and limestone)on the rock-breaking results.The experimental rock samples were scanned by CT and the stress wave propagation theory was applied to reveal the damage mechanism of electrohydraulic effect.The results show that the shock wave compression effect,the stress wave stretching effect and the water wedge effect of the high-speed jet are the main causes of the liquid-phase discharge plasma breaking.With the pressure profile calculated from the shock wave pressure model as the simulation load of spherical wave,the numerical model of rock breaking by liquid phase discharge in infinite formation is established by using the finite element simulation software LS-DYNA,the damage degree of rock and the dynamic response law of rock internal stress under different confining pressure are discussed,and the mechanism of confining pressure restraining rock fragmentation is revealed.