Microseismic Source Vector Inversion

In the process of fracturing and water injection in low permeability oilfield,the real-time monitoring of the micro-seismic events caused by the fault of the underground strata is a hot research topic at home and abroad.In recent years,with the development and maturity of the micro seismic monitoring theory,micro seismic monitoring technology has been widely used in the monitoring of hydro-fracture during the hydraulic fracturing in low permeability oil field.The key problem of micro-seismic monitoring is the accurate location of micro seismic events.Although the signal to noise ratio(SNR)of the borehole micro-seismic monitoring events is relatively high,the inversion localization is sensitive to the arrival times,velocity model and the observing system.Therefore,it is very necessary to improve the accuracy of source location by researching the optimization and improvement method in the borehole micro-seismic monitoring.Combined with the characteristics of borehole micro-seismic monitoring system,firstly studied forward modeling method for the borehole micro-seismic monitoring,respectively using ray tracing method and high-order staggered grid finite difference method for the simulation analysis of micro-seismic events.In the ray tracing method,considered with the reflection wave,and refraction wave travel time calculation,and in finite difference modeling using the seismic moment tensor of the different focal mechanisms sources to simulation and analysis seismic wave propagation characteristics.Based on the micro-seismic location error analysis,discussed the factors affecting the positioning accuracy,theoretically studied effects of various factors on source localization errors,and focused on the study of inversion objective function selection,geophone relative position,velocity model and azimuths on the influence of micro-seismic event location.Proposed the jointed difference information objective function to improve the utilization of the time difference information.Considering the factors that affect the positioning error,summarized the micro-seismic design principles to ensure the quality of the micro-seismic monitoring records.In micro-seismic source location,in order to reduce the uncertainty influence of velocity model,according to the observation of the three component micro-seismic data,constructed the vector objective function with travel time and wave direction,proposed the joint inversion method with the source location and velocity model.The velocity model were adjusted by simulated annealing algorithm.The feasibility of the method was verified by model test.In the actual data processing,establish appropriate observation system and the initial velocity model combine with the work area information,and use the perforating data to correct the initial velocity model,after the initial positioning of the micro-seismic events,using the joint inversion method to repositioning,analyze the results of the micro-seismic events location.