Continuous hypocenter and source mechanism inversion via a Green's function-based matching pursuit algorithm

Abstract

The hydraulic fracturing of rock formations bearing oil and gas is a process that aims to improve well productivity. The breaking of rocks releases seismic energy that is recorded by stations usually located in nearby wells. By processing these recordings, the hypocenters of induced microseismic events are retrieved and interpreted to estimate the fractured volume. Several techniques have been developed to determine hypocenters; the most common are based in the inversion of P- and S-wave time picks from multiple stations (Pujol, 2004). There are also procedures that involve, for example, the back propagation in time of the recorded wavefields (Gajewski and Tessmer, 2005). Besides the hypocenter location of microseismic events, there is additional information embedded in the seismic recordings: the source mechanism, which is expressed via the seismic moment tensor (SMT). Not as common as the estimation of the hypocenter location, the SMT of induced microseismic events is also estimated from monitoring records (e.g., Nolen-Hoeksema and Ruff, 2001; Jechumtalova and Eisner, 2008). The SMT provides an additional source of information for understanding the fracturing process. A quasi real-time system for simultaneous event location and SMT inversion can reduce the processing and interpretation turnaround times. More notably, such a system could facilitate a realistic integration of microseismic geophysical data to significant decisions that are made during engineering operations such as fracturing.