Quantification of the Impact of Seismic Anisotropy in Microseismic Location

Abstract:

Microseismic imaging is commonly used to monitor hydraulic fracturing processes and identify fracture networks. However, microseismic locations could be biased if seismic anisotropy, which is ubiquitous in sedimentary rocks due to either layered bedding or fracturing, is unaccounted in velocity models. To quantitatively assess such biases, we have applied a nonlinear location method to synthetic traveltime data in seven models from isotropy to different levels of anisotropy cases, including vertical transverse isotropy (VTI) and horizontal transverse isotropy (HTI). Synthetic waveforms are recorded at two vertical receiver arrays in a three-layer velocity model using a pseudo-spectral method. Both P and S wave arrivals are used to locate three events assuming an effective isotropic velocity model. The average location error is 59 m for isotropic case, and is 156 m (158 m), 237 m (244 m), and 258 m (265 m) for 5%, 10% and 15% VTI (HTI) cases, respectively. These results suggest that even 5% seismic anisotropy, if not properly accounted, can cause significant biases in microseismic event locations. Therefore, our future work will solve seismic anisotropy jointly while locating microseismic events.