Seismic Response To Segmental Hydraulic Fracturing Of Ground Horizontal Wells And The Coal Burst Prevention Effect Evaluation

As a new type of technology for controlling high-level thick and hard roof coal burst,the staged fracturing of surface horizontal wells is currently lacking in research on the law of microseismic response induced by fracturing and the evaluation of the effect of preventing coal burst.Aiming at the theme of " micro-seismic response law induced by staged fracturing of surface horizontal wells," this thesis analyzes the spatial and temporal distribution characteristics of micro-seismic events in staged fracturing of surface horizontal wells,and analyzes the micro-seismic response of downhole water production,fracturing process parameters and tunneling construction.The mechanism of micro-seismic response induced by fracturing is proposed,and the influence of fracturing process,parameters and tunneling disturbance on micro-seismic response during fracturing is clarified.By establishing a numerical model of fracturing weakening,the influence of lithology parameters,process parameters and natural fractures on the weakening and pressure relief effect of liquid injection is revealed.Focusing on the core of " evaluation of impact prevention effect of staged fracturing of surface horizontal wells," a data optimization method based on microseismic integrity is proposed,and its feasibility is verified.The effect of fracturing on coal burst prevention is evaluated from five aspects: microseismic space-time activity,impact deformation energy distribution,roof pressure change,abutment stress distribution and surface subsidence.In the study of microseismic response law induced by staged fracturing of ground horizontal wells,the microseismic activity is greatly enhanced during ground fracturing,and the microseismic events induced by fracturing mainly come from the fracturing layer.According to the downhole water production during fracturing and the microseismic activity of each fracturing,the response mechanism of fracturing-induced microseismic is proposed.The results of comparing the fracturing process curve with the microseismic time series distribution show that the microseismic events are always generated after the temporary plugging,and the temporary plugging process is the key to induce the microseismic response.The microseismic response is obvious in the early stage of fracturing,but when the injection volume reaches about 1000m3,the microseismic response will be greatly reduced.In the microseismic active area during the excavation period,the fracture is more developed,and the microseismic activity during the fracturing period is weak.In the study of fracturing weakening and microseismic response mechanism,two methods to characterize the weakening effect of liquid injection are proposed,and the influence of rock mass property parameters,fracturing process parameters and natural fractures on the weakening effect is analyzed.The results show that the weakening effect of liquid injection is inversely proportional to the permeability of fracturing layer and proportional to the permeability of diffusion layer.It is proportional to the strength of rock mass of fracturing layer and diffusion layer.The existence of natural fractures will weaken the effect of liquid injection on rock strata.The greater the injection pressure and fluid density,the better the weakening effect.According to the characteristics of the rock parameters of the fracturing induced microseismic response mechanism model,the numerical simulation is carried out.The simulation results verify the microseismic response mechanism.When the diffusion layer is high permeability and high strength lithology,the injection weakening effect is the best,that is,the microseismic response is intense.In the evaluation of the effect of ground fracturing on coal burst prevention and control,a data optimization method based on microseismic integrity is proposed and its feasibility is verified.The results of microseismic activity,abutment stress distribution,impact deformation energy distribution,periodic weighting characteristics and surface subsidence change during the mining period show that the microseismic events during the mining period of the working face after fracturing are mainly in the form of high frequency and low energy.The distribution range of supporting stress is reduced,the peak position is moved outward and the cantilever is shortened.In areas with good microseismic coverage induced by fracturing,the impact deformation energy during mining is low;the pressure period becomes shorter,and the collapse form of overburden rock is decentralized;the surface subsidence is more obvious than that of the working face after mining.It shows that the overburden rock collapse of the working face after fracturing is more timely and sufficient,which can effectively reduce the risk of coal burst.