Study On Evolution And Micro-seismic Distribution Of Hydraulic Fracturing Fracture Networks

In recent years,hydraulic fracturing technology has gradually become one of the core means of permeability improvement in low permeability coal reservoirs.In order to evaluate the effect of hydraulic fracturing on increasing permeability,it is necessary to describe the evolution process and expansion morphology of hydraulic fracturing fractures.Based on the research background of 3# coal reservoir in gaohe mining area,this paper adopts the research method of combining theoretical analysis,experimental research,numerical simulation and on-site micro-seismic monitoring to reveal the water-force coupling process formed by hydraulic fracturing fracture network,the fracture form of reservoir coal and rock and the damage evolution rule.Firstly,through the analysis of the influencing factors of coal reservoir permeability and the conceptual modeling of pore pressure formation process,the weak coupling finite element equation of percolation-pore elastic coupling was established.Through the calculation of an example,it was found that the permeability of coal reservoir firstly gathered along the direction of maximum principal stress to form pore pressure field in the process of hydraulic fracturing.Then,based on the understanding of mohr-coulomb criterion tension and shear,the damage constitutive relation of hydraulic fracturing failure is established,and the acoustic emission characteristics of the two failure forms are tested and observed.The results show that during the loading process of the tensile test,the stress intensity reaches the peak value,the rock basically loses the load-bearing capacity,and the acoustic emission activity,number of impacts and number of energy disappear simultaneously.In the shear test,the number of ae impacts and energy increases and maintains at a high level after the rock reaches the peak stress intensity.Finally,numerical simulation and field microseismic monitoring are carried out for the 3# coal seam hydraulic fracturing well in gaohe mining area.(1)the numerical simulation results show that the expansion of the hydraulic fracturing cracks along the maximum principal stress direction(that is,the north east 60 °),the fracture morphology in ellipsoid distribution and fracture network distribution in roof and floor is less,and along the height direction of the reservoir permeability and permeability is smaller than coal seam roof and floor,which broke through the traditional hydraulic fracturing model of single fissure;(2)the field microseismic monitoring shows that the main fracture direction along the north east 40 ° ~ 75 ° direction,and from the micro seismic monitoring four dimensional figure can observe reservoir height and width are microseismic monitoring data points;(3)through numerical simulation and mutual support of microseismic monitoring,the hydraulic fracturing of main crack along the horizontal maximum principal compressive stress direction,north east 60 °,and development of hydraulic fracturing cracks in web forms is not a single parallel plate crack,if considering reservoir RVE cell growth of microcracks,nucleation,connection,the hydraulic fracturing.