Joint velocity and event location inversion workflow in microseismic reservoir monitoring

Abstract

Time-controlled sources at known locations are desired to calibrate the velocity models used for microseismic reservoir monitoring. However, having such sources is not always possible, particularly when dealing with carbon capture and underground storage (CCUS) or geothermal surveys. A joint velocity and event location inversion approach is a promising candidate to help address this issue, though it is not yet a de facto industry standard due to several practical challenges remaining. We developed a workflow of a joint velocity and event location inversion method in the case of a 1D vertical transverse isotropy (VTI) velocity model. The algorithm uses the travel time and polarization angle of the data and then minimizes the residual by updating the velocity model. The resolution of the velocity model update gradually increases during the iteration. The workflow provides intuitiveness to the processing compared to the previous approaches. With this new approach, we can optimize the resolution that the initial velocity model has while intuitively controlling the resolution of the inverted model parameters and assessing the invertibility.