Relative source location using a local equivalent path strategy for surface microseismic monitoring

Microseismic monitoring has become a tool of choice for the development and optimization of oil and gas production from unconventional reservoirs and is also used to help assess and reduce the risk of induced seismicity. Recently, relative location methods, which can greatly improve the relative location accuracy among nearby events, become popular and attract the attentions of many researchers. However, how to quickly and accurately capture the location of microseismic events remains a big challenge. We introduce a novel relative event localization technique which utilizes the similar spatial distribution characteristics of the propagation paths of the master event and the adjacent microseismic events to simultaneously achieve quick location estimation and reduce the dependency on a velocity model. The ray paths above the suppositional observation plane are reasonably simplified by employing the propagation paths of a master event to act as the equivalent paths of the adjacent events. Moreover, an iterative technique is used to update the suppositional observation points according to the location result of the previous step and then relocate the event to eliminate the location error caused by the previous hypothesis. In addition, a calibration method is applied to correct the location error caused by an inaccurate velocity model. We test the performance of the proposed technique on both synthetic and field data examples. The results suggest the proposed method significantly improves the location accuracy and reduces the dependency on a velocity model by sufficiently exploiting the master event information. Furthermore, the proposed method is excellent in computational efficiency so that can meet the requirements of real-time locating. In addition, the technique can be beneficial in other fields associated with locating, such as aftershock localization of earthquakes, volcanic earthquakes, etc.