Analysis Of Variation Law Of Volcanic Reservoir Stress Fields In Horizontal Well Staged Fracturing

At present,horizontal well fracturing is one of the core technologies for developing volcanic rocks.Hydraulic fractures can communicate with natural fractures and complex fracture networks can be constructed to increase the conductivity of horizontal wells.Fracturing construction changes the distribution of the original formation stress,and also affects the extension route of the subsequent hydraulic fracture.Based on the established mathematical model,this paper considers the theoretical relationship between microcracks and main cracks and introduces it into the crack problem.The natural cracks will increase the stress intensity factor at the tip of the hydraulic crack.The sensitivity analysis of the analytical model is carried out.Then the numerical model of the fracturing stress field is established.The distribution of stress field under the influence of different natural fracture parameters,formation parameters and hydraulic fracture parameters is determined.The result will be compared with the results of the analytical model.The following conclusions are obtained through experimental and theoretical research:(1)The original natural cracks in the volcanic rocks will increase the stress intensity factor of the hydraulic cracks that are first pressed.Therefore,the influence of natural cracks cannot be ignored.(2)The lower horizontal stress difference coefficient and Poisson's ratio will affect the crack initiation and expansion of the post-pressure crack.(3)The influence of natural crack parameters in the numerical model is not obvious,but it can be seen from the distribution of the horizontal stress difference coefficient cloud map that the stress steering.It has obvious disturbance effects in the mathematical model.(4)The effect of natural cracks on hydraulic cracks is a short-range effect,both enhanced and weakened,depending on the relative position of the two.The minimum value of K_I is dominated by natural fractures near its tip,independent of natural fractures in other orientations;the maximum value of K_I depends on the distribution of the overall natural fracture group.(5)In the design of the actual fracturing scheme,the optimal value of the hydraulic fracture parameters should be determined as much as possible under the premise of comprehensively considering the influence degree of each factor on the stress field.