Anisotropic Velocity Model Inversion for Imaging the Microseismic Cloud

We present an anisotropic velocity model inversion method that uses multiple sources at known locations to calibrate the velocity model for microseismic hydraulic fracturing monitoring (HFM). We parameterize the perturbation of the initial velocity structure using 2 parameters for the vertical P- and S-wave velocities and 3 parameters for anisotropy, reducing the number of unknown parameters and making calibration fast. This workflow is applied to actual HFM jobs where the initial velocity model is constructed from sonic logs and the calibrated model is used for event detection and location. The inversion for both vertical velocity and anisotropy for this dataset leads to an improvement in location accuracy.