Localization for Surface Microseismic Monitoring Based on Local Equivalent Path and Virtual Field Optimization Method

In the field of oil and gas exploration, microseismic (MS) monitoring has long been utilized in hydraulic fracturing to assess reservoir enhancement treatments and mitigate the risk of induced seismic activity. The fundamental task of MS monitoring is to locate MS events resulting from rock fracturing during the fracturing process, serving as the foundation for other advanced processing procedures. Surface monitoring has gained popularity over downhole monitoring due to its cost-effectiveness and flexibility, despite potentially lower data quality. Therefore, the development of high-precision and robust surface monitoring localization algorithms is of great importance. In this study, we propose a novel method for localizing MS events based on a local equivalent path (LEP) and virtual field optimization method (VFOM), which reduces the reliance on velocity models and precise time picking. Our method begins by establishing a hypothetical observation surface (HOS) and simplifying the propagation paths above it to equivalently transfer the surface geophones. Then, by combining VFOM with an iterative algorithm to determine the intersection of hyperbolas from the geophone pairs, we achieve the accurate localization of MS events. Extensive testing using synthetic and field data confirms the high accuracy and stability of the proposed method, even in the presence of errors in velocity models and arrival-time picking. Furthermore, our approach exhibits high computational efficiency, making it suitable for real-time localization requirements.