Microseismic Location Based On Reverse Time Ray Tracing

Microseismic monitoring is a technology that has a wide application foreground,in recent years in the shale gas extraction,low permeability oil and gas field development,geothermal,mining and other fields has been widely used.The most important part of microseismic monitoring relies on precise location of microseismic events,which is the focus of scholars to research.Based on the theory of ray method,this paper has carried on the corresponding numerical simulation research on the three parts of the microseismic of forward calculation,data processing and event location,and has made some achievements.For the forward calculation of microseismic events,a relatively simple ray tracing method is chosen for implementation.The explicit formula of transmitted wave transmission vector in two-dimensional and three-dimensional model is deduced,which can be applied to various continuous geological interfaces.The ray path and the time curve are obtained by the forward calculation under the two-dimensional and three-dimensionalmodel by the shooting method and segmented iterative ray tracing method.After considering the spherical wave diffusion and the transmission energy loss of the interface,we get the synthetic record for subsequent precessing.On the basisi of the synthetic seismic record,the mircoseismic first arrival time was obtained by using time window energy ratio method.Then I selected some sample data before and after the arrival time to get the direction vector of the seismic wavefront incidenced in the detector by polarization analysis.In the method of seismic location based on the information of travel time,I choosed the Inglada method and Geiger method for microseismic location in the homogeneous medium based on the forward calculation data.The source parameters obtained by Inglada method are taken as the initial conditions,and the more accurate source position is obtained by Geiger method.In this paper,an reverse time location method based on polarization analysis is proposed,and numerical simulation is carried out under two-dimensional and three-dimensional layered models.In the three-dimensional horizontal layered medium,the accuracy of the reverse time location method is higher than that of the Inglada,which is slightly lower than that of the Geiger method,but the accuracy of the travel time is higher than that of the above two methods.Finally,the location of the reverse time ray tracing method is carried out under the three-dimensional arbitrary interface model,and good results are obtained.