Numerical Simulation Of Fracture In Perforated Shale

In recent years,shale gas development has increasingly become the focus of international attention.Shale reservoirs need to be improved by hydraulic fracturing.Because perforated completion is commonly used in a shale gas well,the cracks caused by perforation are usually the initial condition for hydraulic fractures initiation and propagation.These cracks affect the effectiveness of hydraulic fracturing,therefore it is necessary to investigate the crack distribution law in perforated shale.In this paper,finite element program generation system(FEPG)was used to simulate loading,apply confining pressure and build the model for numerical simulation.With the random distribution of loaded material strength,it is possible to crack randomly.After calculation,the results were compared with the corresponding experimental results.The morphology and width distribution of cracks around the bullet hole were analyzed.And influence of loading and confining pressure on cracks distribution was explored.There were four damage forms from the perforating tunnel to the outside: compressionshear damage zone,severe tensile damage zone,tensile damage propagation zone,undamaged zone.There was almost no tensile crack in compression-shear damage zone.In severe tensile damage zone,tensile cracks rapid increased.Radial cracks gradually decreased in tensile damage propagation zone,and were more distinct.Wide cracks were near the bullet hole,and narrowed as the radius increased.The tensile damage propagation zone significantly enlarged as load increased.It means that the cracks around the bullet hole can be lengthened by increasing the perforation diameter of bullet.The tensile damage propagation zone significantly reduced as confining pressure increased.It means that perforation would have less impact on hydraulic fracture initiation as reservoir burial depth increased.