A new microseismic location method accounting for the influence of the hydraulic fracturing process

In the hydraulic fracturing process, the velocity model of traditional inversion is usually constructed by well logs, seismic data or calibration shots. The variation of pore pressure and fractures in this process has a major influence on the velocity. However, this influence is usually ignored in the velocity estimation model. In this paper, we propose a new microseismic location method that accounts for the influence of hydraulic fracturing on velocity. Firstly, we simulate the 3D hydraulic fracturing process based on mass conservation, the seepage equation and fracture mechanics. Then the equivalent velocity model is constructed using the Coates–Schoenberg method and fracture compliances. The 3D ray-tracing method is applied to forward-model the microseismic data and traditional inversion methods are applied to locate events and analyse the inversion error. Finally, we introduce a new method, called the equivalent velocity inversion method (EVIM), taking into account the influence of the fracturing process. The simulation results show that the hydraulic fracturing process affects the velocity and thus makes the inversion accuracy of the same receiver array vary considerably with the sources in the traditional methods. The new EVIM can effectively reduce the inversion error.