Numerical Simulation Of Rock Damage Law Around Perforation

As human beings develop and utilize oil and gas resources gradually,conventional oil and gas resources are continuously consumed and cannot meet human needs.Unconventional oil and gas resources have gradually become the focus of attention all over the world.Compared with conventional oil and gas resources,unconventional oil and gas reservoirs have poor physical properties.It is usually unable to reach the industrial oil flow if depending on the energy of the reservoir itself.Therefore,it is necessary to perform stimulation measures such as perforation,fracturing etc.before it can be put into production.The cracks generated by the perforating operation on the rock around the perforation are the initial conditions for the fracturing operation thus have a great influence on the fracturing results.Therefore,it is necessary to study the damage law of perforating operations on the surrounding rocks.In this paper,the finite element numerical simulation method is used to solve the problem.Finite Element Program Generator(FEPG)is used to generate the calculating code.According to the working principle of perforating operation and the process of the metal jet penetrating on rock,a numerical model is established for the simulation calculation.A cross-section of a cylindrical target was selected as the research object.To ensure the randomness of the crack distribution,the strength parameters of rock material are randomly distributed in space.Using the dimensional analysis method to analyze the penetrating process.The results of physical experiment are used to compare with the numerical simulation results.The influence of confining pressure and loading conditions on the crack distribution around perforation law are analyzed.The simulation results show that after the perforating operation,the broken cross section of the target can be divided into four regions from the inside to the outside: the central smashing zone,the compression-shear damage zone,the tensile damage concentration zone and the tensile failure propagating zone.There are a large number of damage elements with wide crack width connected with each other in the central smashing zone.In the compression-shear damage zone,there is almost no tensile damage elements and a great number of compression and shear damage elements.A large number of tensile cracks are generated in the tensile damage concentration zone,and the number of cracks increases rapidly,and the crack width of cracks in this zone is larger.The number of cracks in the tensile failure zone is gradually reduced in the tensile failure propagating zone,the width of cracks is gradually reduced,the crack is more distinct and expands radially.The extension of the tensile failure propagating zone increases rapidly under greater inner load or lower confining pressure.