Congcong Yuan , Jie Zhang

Passive seismic tomography plays a significant role in monitoring subsurface structures and properties during hydraulic fracturing. In this study, we develop a new passive seismic tomography approach to jointly invert for event locations, 3D P-wave velocity (Vp), and Poisson’s ratio models, for downhole microseimic monitoring The method enables to directly obtain the 3D Poisson’s ratio or Vp/Vs ratio without the assumption of identical P- and S-wave raypaths. We incorporate the back azimuths of passive seismic events into the proposed method to better constrain the event locations. We also apply the 3D cross gradients to the proposed method in order to assimilate the P-wave velocity model with Poisson’s ratio model in geological structure. The synthetic experiment demonstrates that the proposed tomographic method is able to recover the event locations and their neighboring 3D P-wave velocity as well as Poisson’s ratio models effectively. In the field experiment, microseismic events are relocated reasonably compared with the grid search solutions in a calibrated layer model. The area with low Poisson’s ratios may be utilized to estimate the stimulated reservoir volume and indicate a potential area associated with highly saturated hydrocarbon.