Joint location and source mechanism inversion of microseismic events: benchmarking on seismicity induced by hydraulic fracturing

TLDR

Seismic monitoring can be improved by imaging low‑signal‑to‑noise events, which can be achieved through migration‑type stacking of waveforms from multiple stations. The authors aim to develop a method that locates seismic events with lower SNR than individual receivers by stacking seismic phases and amplitudes. The method stacks phases and amplitudes along diffraction traveltime curves with polarity correction from simultaneous moment‑tensor inversion, calibrates a velocity model with perforation shots, processes 3 d of hydraulic‑fracturing microseismic data, and benchmarks migration‑type locations against manually located large events. In a hydraulic‑fracturing case study, the technique automatically located mostly shear events forming narrow bands about 100 m above injection intervals and proved feasible for real‑time monitoring.

Abstract

SUMMARY Seismic monitoring can greatly benefit from imaging events with a low signal-to-noise ratio (SNR) as the number of the events with a low signal grows exponentially. One way to detect weaker events is improvement of a SNR by migration-type stacking of waveforms from multiple stations. We have developed a new method of location of seismic events that involves stackingofseismicphasesandamplitudesalongdiffractiontraveltimecurvestosuppressnoise and detect seismic events with a SNR lower than that on individual receivers. The stacking includes polarity correction based on a simultaneous seismic moment tensor inversion and detection algorithm on the stack function. We applied this method to locate microseismicity induced by hydraulic fracturing. First we calibrated the velocity model by locating perforation shots at known locations. Then we processed 3 d of data from microseismic monitoring of shale stimulation and benchmarked migration-type locations of the largest events that were manually located. The detected and located events induced by hydraulic fracturing in this case study are mostly shear events forming narrow bands along the maximum horizontal stress direction approximately 100 m above the injection intervals. The proposed technique is fully automated and feasible for real-time seismic monitoring.