Congcong Yuan , Xiong Zhang, Jie Zhang

Several studies suggest that shale sweet spots are likely associated with low Poisson’s ratio in the shale layer. Compared with conventional geophysical techniques with active seismic data, it is straightforward and cost effective to delineate the distribution of 3D Poisson’s ratio using microseismic data. In this study, we develop a method for determining microseismic event locations, 3D P-wave velocities, and the Poisson’s ratio model with data recorded from downhole monitoring arrays. The method combines the improved 3D traveltime tomography, which can invert P and S arrivals for 3D P-wave velocity and Poisson’s ratio structures simultaneously, and a 3D grid search approach for event locations in an iterative fashion. The traveltime tomography directly inverts the Poisson’s ratio strucure instead of calculating the Poisson’s ratio from P- and S-wave velocities that are inverted by conventional traveltime tomography separately. The synthetic results and analysis suggust that the proposed method is capable of directly recovering the true Poisson’s ratio model. We also apply the method to a field dataset, and the results show that it helps delineate the structure of the reservoir and identify shale sweet spot.