Study On The Expansion Pattern Of Double Fractures In Shale Under The Action Of High Voltage Arc Penetration Liquid Water Surge

With the continuous improvement of domestic science and technology and the proposal of the concept of carbon neutrality,the demand for clean energy is increasing.Conventional oil and gas cannot meet people’s increasing demand for energy,so the commercial development of unconventional oil and gas resources is particularly important.Shale gas reserves in China rank among the top in the world.As an unconventional oil and gas resource,shale gas is a supplement product of conventional natural gas,which is widely accepted by the society because of its characteristics of high heat and low pollution.However,due to the special geological reservoirs in China,the permeability of shale gas reservoir is poor,so it is necessary to carry out deep reservoir transformation to improve the fracturing effect and permeability of shale gas reservoir,so as to increase the production of shale gas.High pressure liquid phase electric pulse discharge cracking and antireflection is a new technology for oil and gas extraction in recent years.Due to its good cracking effect,low pollution,low energy consumption and other characteristics,researchers and relevant personnel in this field pay attention to it.However,due to the late start of this technology in China,the research on the mechanism and application of this technology needs to be improved.Theory research of this paper through the laboratory test and numerical simulation method of combining the electric effect of shock wave for use under the double law of crack propagation is studied of liquid water discharge pulse shock wave generation and propagation characteristics of superimposed stress field under the stress of double fracture crack and crack propagation criterion the theoretical research on three aspects;Then through the laboratory drilling water injection high voltage electric pulse discharge crack test,the prefabricated crack propagation morphology and evolution law of different Angle and different length between the two cracks were studied.Finally,numerical simulation is further used to verify and analyze the double fracture propagation law under different discharge voltages and different in-situ stress changes,which can provide reference for related projects.The main research results are as follows:(1)Set up by the water shock stress in-situ stress and disturbance on hydraulic fracture stress of diameter to well superimposed stress field model,selection of maximum energy release rate as a crack propagation criterion,reveals the liquid electricity water shock wave with the interference mechanism of radial double crack extension for drilling the water discharge shock crack radial double provide theoretical basis for crack extension.(2)The control variable method is used for liquid discharge water shock rock crack page similar to the physical experiment research,through laboratory test,discharge voltage,ground stress,initial state double crack length is constant,with the increase of double seam crack initial Angle,the expansion of the crack length and the maximum seam width(opening),double cracks in the opposite direction have deflection Angle;With the increase of initial fracture length,the stress disturbance increases,and the fracture length and width decrease.It can be seen that the stress interference factors in the process of double(multiple)fracture propagation cannot be ignored.(3)Abaqus-xfem finite element numerical analysis software was used to study the shale caused by liquid discharge water shock wave.Through numerical simulation,it can be found that with the increase of in-situ stress difference,the fracture is deflected towards the direction of maximum principal stress,and in-situ stress becomes the key factor affecting the fracture propagation morphology crack extension pattern.At the same time,due to the phenomenon of stress decline in the process of water shock wave propagation,the acquired energy of the initial long fracture is lower than that of the short fracture,resulting in the extension length of the initial long fracture is lower than the extension length of the short fracture.Therefore,the hydro-electric water shock fracturing technology is beneficial to realize the reservoir transformation.(4)Through numerical simulation,with the increase of discharge voltage under the condition of constant water pressure,the peak action intensity of water shock wave increases,the fracture initiation pressure increases,the fracture extension length and the maximum fracture width increase,and the anti-reflection effect of fracturing is better.