Mesomechanical Simulation On Damage Process Of Saturated Rock During Hydraulic Fracturing

Large-scale stimulated reservoir volume fracturing has become the key to the effect development of unconventional oil and gas reservoirs.The degree of fracture network development is the key factor of fracturing effect,especially the original microcrack initiation and propagation in brittle formation.However,the current numerical simulation of hydraulic fracturing,in which only natural crack and manual macrocrack coupling is considered,is relatively weak in simulation research of rock damage evolution mechanism.Hence,this topic based on the theory of micro-macro rock damage starts from the evaluation and improvement of stress intensity factor model for micro sliding crack in saturated brittle rock.Furthermore,the constitutive model of saturated rock with micro sliding crack has further improved by combination with micro sliding crack model and crack propagation criterion.Then the constitutive model of saturated rock with micro sliding crack has been embedded in ABAQUS simulation software,and rock damage dynamic distribution during hydraulic fracturing is achieved.Through the numerical simulation of fracturing fluid injection and shut-in processes,the phenomena and laws in rock dynamic damage process were researched,and the influences of the rock physical parameters and construction parameters on the rock mechanical properties and rock damage process were analysed.The results show that microcrack morphology and microcrack density are main factors that effect on rock strength,which means when the shape of microcrack is closer to the liner crack,and more favor for rock failure.The step-like phenomena of the stress-strain curve under compressive loading is the macro-response of sliding displacement behavior.Moreover,with crack density and confining pressure increasing,the nonlinear features of rock stress-strain curve are more prominent.In addition,when rock permeability,microcrack density,injection displacement and fluid viscosity increase,the damage speed and area increase.For brittle rock with micro sliding crack,moderate injection time reduction and shut-in process cause damage degree of rock to continue to increase during shut-in process.The achievements in this thesis are quantitatively characterizing the damage degree of rock near macro manual crack and crack growth behavior,which can provide the theoretical foundation for hydraulic fracturing technology design of saturated brittle rock reservoir.