Study On The Optimization Of Perforating To Form Network Cracks In Shale Gas Reservoirs

Shale gas reservoir fracturing effect directly affect the effect of shale gas development.Shale gas reservoir fracture network mechanism research and perforating technology optimizationare the important scientific problems of effective development of shale gas.How to optimize perforating technology and subsequent fracturing cracks,is one of the important conditions to determine whether shale gas reservoir fracturing success,therefore,the optimization of perforation technology and the shale fracture network formation mechanism research is of great significance fordevelopment of shale gas.In this paper,fracture network formation mechanism was researched on the basis of thetheories of rock mechanics,four mechanical condition to formnetwork cracks in the process of shale gas reservoir perforation fracturing.The fracture mechanism of shale and fracture pressure were studied and calculated on the basis of perforating well borehole surrounding stress field distribution model.The corresponding finite element model was established based on finite element software ANSYS,and to compareand analyzethe effectof different perforating parameters(perforating azimuth angle,perforating density,perforation diameter,perforation tunnel length)and perforation modeon formation fracture pressure.The relationship between hydraulic fracture and natural fracture are studied on the basis of thetheories of two-dimensional linear elastic and three-dimensional fracture.The two-dimensional and three-dimensional interference model of hydraulic fracture and natural fracture was established to research the mechanical condition ofshearing slippage damage and opening for natural fractureand the influence factors of fracture surface slippagein the process of fracturing.It is shown that horizontal differential principal stress,approaching angle,cohesion,the angle between horizontal wellbore and natural fracture and coefficient of friction are the main factors to cause natural fractureshearing slippage damage.In the condition of low approaching angle(30°-60°),low cohesion,low coefficient of friction and the angle between horizontal wellbore and natural fracture is 90°,the fracture pressure is low,so shearing slippage damage is easy to happen.Crustal stress,approaching angle,the angle between horizontal wellbore and natural fracture,pump rate,the size of natural fracture and fracture net pressure are the main factors to determine whether the natural fracture opening.Fracture surface slippage was influenced by approaching Angle,the angle between horizontal wellbore and natural fracture,crack size,elastic modulus and Poisson's ratio.Fracture surface slippage is higher in the condition of larger crack size,smaller elastic modulus and Poisson's ratio,approaching Angle of 30 °-60 ° and the angle between horizontal wellbore and natural fracture is 90°,at this time the fracture activating result is better.The influence of network cracks formationby comparing the different construction ways(sequential fracture ? ends of fracure ? jumping fracture)shows that,fracturing effect of jumping fracture is best and beneficial to form network fracture system.The results of the study has important guiding significance on shale gas reservoir fracture network mechanism research and effective development of shale gas.