Micro-seismic Source Location Inversion Based On Ray-theory 2D Forward Model

Micro-seismic monitoring technology is the latest technology with broad application prospect, it can implement the fracture monitoring and real-time monitoring of reservoirs after water injection and gas injection, which is meaningful to exploration and development of reservoirs. The core of micro-seismic monitoring technology is the exact location of micro-seismic events. In this paper, we have researched the forward modeling, the inversion algorithms and seismic phase identification and inversion of micro-seismic events, and realized the high precision inversion and location of micro-seismic source.According to the characteristics of well micro-seismic monitoring, after the discussion of advantage and disadvantage of shooting method, iterative method and bending method, we have researched the iterative ray tracing method of tilt layered medium significantly, and realized the forward modeling of transmission, reflection, refraction in tilt layered models. In the horizontally layered medium, comparison between forward result of shooting method and that of iterative method has proved that this method is right and has high precision and efficiency.Combined with real micro-seismic signals, on the basis of discussion about the inversion precision and applicability of grid search method, conjugate gradient method and genetic method in micro-seismic inversion problems, we propose the joint inversion of the grid search method and genetic method based on the solution domain constraints according to the advantages of these methods, decrease the impacts of velocity structure and first arrival perturbation on the inversion and make the inversion more stability and reliable.As to the problem that single one event in the seismic records appears in the later period of fracture, through the analysis about impacts of seismic source location, receiver location and interval velocity on first arrival difference, we research seismic phase identification of micro-seismic events technology using time difference of any two traces. Also we establish the S wave velocity correction method using modeling of P wave well logging and constraint of perforation data which can decrease the impact of velocity perturbation on inversion results in S wave inversion.In the light of possible problems in the real inversion, such as perturbations of first arrivals, variation of velocity structure around the whole fracture, we design the methods such as selecting weight factor, constructing stable single-value function and using more stable inversion algorithm to improve the robustness of inversion. After the inversion of real micro-seismic dataset in an area of China, analysis of development feature and dispersion feature of micro-seismic events as well as the structure of fracture area compared with the results of Pannical Cooperation, have proved the validity of this inversion system.