Microseismic Event Location Using Time Reversed Imaging Based on Decoupled Wavefields in VTI Media

Locating microseismic events in a reservoir monitoring system is of great significance due to its capacity of delineating the induced fractures. Time reversed imaging (TRI) method, which refocuses the back-propagated seismic energy to its real origin, has been demonstrated as a reliable location technique especially in noisy data processing. However, the time reversed images are often contaminated with strong imaging artifacts due to the cross talk of coupled wave modes coinciding in time and space especially in anisotropic media, leading to unreliable location estimations. To minimize the interference of strong imaging artifacts, we present a TRI technique based on decoupled wavefields. Spatial filters constructed based on Christoffel equation are applied to separate qP and SV wave modes. The auto and cross-correlations of decoupled qP and SV potentials are then applied as the image conditions to form the final location images. The synthetic example has shown that the spatial filters can fully separate the wave modes in 2D VTI medium compared to Helmholtz decomposition, leading to an improved location images with a much sharper focus.