Microseismic event localization using surface and borehole data

Localization of induced microseismic events is a vital element of passive seismic monitoring. Currently, a variety of techniques for localization of microseismic events are available in the literature. There are two almost independent branches of methods of microseismic monitoring, namely, surface monitoring and borehole monitoring, that are characterized by significantly different input data, processing steps, velocity models and inversion algorithms. The mentioned above differences result in the mismatch of hypocenter locations of microseismic events obtained independently from the surface and borehole data. In this work, we investigate the opportunity of microseismic event localization using simultaneously the borehole and surface data and propose a new approach for joint localization of surface and borehole observations. In our approach, we independently calibrate velocity models for localization of surface and borehole data using information about perforation shots visible on both datasets. Additionally, we propose to select several large-magnitude events visible both on the surface and borehole datasets and enforce their locations, obtained independently from the surface and borehole data, to coincide. We formulate the joint localization problem in a probabilistic fashion. We demonstrate the performance of the proposed algorithm on realistic synthetic and on the field data example. The comparison of the location results of clouds of microseismic events, obtained by inversion of borehole data, surface data, and the proposed joint inversion, clearly demonstrates that for the majority of events the joint inversion provides superior results compared to other methods.