Source Mechanism Analysis of Single-Well Microseismic Data Using Full-Wavefield Moment Tensor Inversion

Abstract

Receiver angular coverage of microseismic sources occurring during hydraulic fracturing treatments is an important factor to consider when interpreting moment tensor inversion results. A horizontal receiver array can provide greater angular coverage of vertical failure planes than a vertical receiver array. The source orientation can be accurately determined if the array samples both sides of the failure plane. However, the compensated-linear-vector-dipole (CLVD) mechanism can be overestimated by up to ~40% for double-couple (DC) sources and the isotropic mechanism can be overestimated by ~70% for CLVD sources. Source mechanism constraints on the moment tensor inversion are used to mitigate the lack of angular coverage. The use of the deviatoric assumption decreases the error in the source mechanism to ~70% for DC sources and ~50% for CLVD sources however this introduces an error of ~55° in the strike of the CLVD source. Moment tensor inversion programs typically assume isotropic velocity models however rocks can have anisotropic seismic velocities. Inversion of sources occurring in anisotropic media but assuming an isotropic velocity model in the inversion results in source orientations with errors < 15° and up to 80% error in the resolved source mechanism.