Shale Hydraulic Crack Propagation Mechanism And Microseismic Monitoring Analysis

With the increase in energy requirements,shale gas has attracted people's attention with its rich reserves.However,compared to conventional reservoirs,shale gas reservoirs have more complex geological conditions,lower reservoir permeability and worse diversion capacity.Therefore,the reservoir must be fractured and reformed.Under the influence of shale bedding and natural fracture development,the effect of fracturing reconstruction of shale reservoirs is difficult to meet the requirements of a project design.In order to obtain a better effect of fracturing,it is necessary to monitor the fracturing state in real time,analyze the effect of fracturing,determine the engineering geological problems encountered by fracturing,and modify the fracturing parameters.Therefore,more and more researchers pay attention to crack propagation mechanism during the hydraulic fracturing in shale gas reservoirs.Based on the method of theoretical analysis,numerical simulation and engineering practice,crack propagation mechanism during the hydraulic fracturing is analyzed from the crack length,direction,reservoir mechanics and natural fracture.The main contents of this thesis are as followed:(1)A finite-width plate model with central fractures is summarized.The distribution of the elastic-plastic stress field near the crack tip due to the action of the uniform water pressure is analyzed.Based on the analytical solution of the radius of the plastic zone,the variation rule of the crack propagation length with the crack surface uniform water pressure,the central crack half length,the plate width and the shear yield strength is studied.(2)Fracture propagation model with center slanting cracks acted by confining pressure and water pressure was established.Based on the theory of pseudo-force method,superposition principle and fracture mechanics theory,the stress intensity factor of the tip of the inclined crack is studied,and then the strain energy density factor theory is used to analyze the variation law of the crack propagation direction with the inclination angle of the crack,the water pressure and the differential stress between confining pressure in the ?-?compound crack propagation mode.(3)Using the extended finite element method,the numerical model of hydraulic fracturing under single perforation condition is established.The influence of the elastic modulus,tensile strength and Poisson's ratio on the crack propagation shape is analyzed.And the,in the numerical model,natural fracture with a certain thickness and filled is considered,and the law of hydraulic fractures is analyzed when the hydraulic fractures is close to natural fracture,passe through natural fractures and spread within natural fractures.(4)In order to solve the problem of superimposed interference of the source signal in micro-seismic monitoring,the synchronous compression wavelet transform signal separation method is optimized by the adaptive harmonic model,and then solve the problem of the initial motion distortion of the signal component separated from the original signal.It can provide a good signal basis for monitoring the state of hydraulic fractures in real time by micro-seismic monitoring.(5)Finally,the fracturing dynamics in the actual fracturing construction are analyzed by combining the hydraulic fracturing construction parameters and the micro-seismic monitoring data.The content and results of this thesis have some reference significance for real-time monitoring and analysis of fracturing treatment state and real-time optimization of construction parameters in hydraulic fracturing construction.