A hybrid workflow for updating 1D velocity model and microseismic event location

An accurate velocity model is critical for determining the microseismic event locations. Simultaneous inversion and alternating inversion are two common strategies for updating the 1D velocity model and estimating event locations in downhole microseismic monitoring. Numerical experiments demonstrate that the limited distribution of the receivers and the coupling between the event locations and the 1D velocity model may lead to an ill-conditioned problem for simultaneous inversion. Thus, a good initial estimate is critical to producing a stable solution. Moreover, the alternating inversion decouples event locations from the velocity model, but it converges to the optimal solution very slowly. In this study, we present a hybrid workflow to update both the 1D velocity model and microseismic event locations by combining two strategies. We first acquire an initial solution with the alternating inversion and then conduct the simultaneous inversion with the alternating result as the starting values. Numerical tests and field data are applied to demonstrate the effectiveness of the hybrid workflow.