Microseismic Focal Mechanism Inversion

With the increase of social development demand for energy,conventional oil and gas resources of mining is being exhausted in the decades,so it is more and more important to explore and develop unconventional oil and gas resources.People often use hydraulic fracturing technology to reform the target layer to increase the rate of oil and gas recovery in the exploration of unconventional oil and gas of low permeability reservoirs or in the development of shale gas.While micro seismic monitoring technology along with the fracturing technology has also played an important role.In recent years,micro seismic monitoring technology has been continuously developed and accumulated,mainly includes: optimization of micro seismic observation system,weak signal extraction and recognition of micro seismic events,micro seismic inversion,micro-seismic fracture interpretation and research of micro-seismic source mechanism.Forward simulation of micro seismic often takes the method of ray tracing.While the calculation speed is fast and the propagation path is clear,this method could not clearly reflect the wave field characteristics of micro seismic propagation.When it comes to study of micro seismic mechanism,track forward method is no longer applicable.This paper firstly studies the micro-seismic source mechanism and discusses the loading methods of the mechanism of different source.On the theory of wave equation and calculation method of finite difference,this paper has realized the wave equation forward modeling of different focal mechanisms.At the same time,this paper has realized the forward modeling of different resources types in different media models to simulate and analysis the seismic wave field characteristics of different focal mechanisms.Travel-time inversion is often used in the orientation of micro seismic inversion.In the process of positioning realization,the distance information(longitudinal distance Z and radial distance R)can be obtained by walking time inversion and take polarization analysis of three component information received by geophones to get the azimuth information(?),so as to obtain the source location(x y z,,).Factors that affect the precision of distance information and accuracy of azimuth angle are analyzed.According to the forward simulation data,the influence of different source types on the other side angle is calculated quantitatively.Considering the limitations of micro seismic travel-time inversion on large seismic offset,the inversion method based on waveform matching is proposed.When the micro seismic events happen far,distance information obtained by the waveform inversion is more accurate than travel-time inversion.Since the moment tensor parameters is too many in micro-seismic focal mechanism inversion,the speed of using the grid search method is too slow to meet the actual requirements when considering the precision and accuracy.As a result,the differential evolution algorithm is used to speed up the inversion,which could obtain the exact moment magnitude and solution information of focal mechanism in the calculation...