Estimation and interpretation of high-confidence microseismic source mechanisms

Abstract

Some of the advantages of surface microseismic monitoring can be examined to suggest ways in which those advantages can improve the use and interpretation of microseismic results. In particular, surface microseismic monitoring provides an opportunity to determine the source mechanism for most events, and methods are available that can increase the confidence in those results. One method for determining microseismic source mechanism is imagedomain pattern recognition (IDPR), which is more suitable to the relatively noisy environment of surface microseismic monitoring than the classic time-domain methods are. One drawback that must be addressed is that accurate image-domain pattern recognition requires the use of 3D velocity corrections. Finally, microseismic events with high-confidence locations and source mechanisms can be used to directly construct discrete fracture networks (DFN).

Single-well moment tensor inversion of tensile microseismic events

“…Inversion of full moment tensors M, quantified by six independent components (e.g., Aki and Richards, 2002;Shearer, 2009), a well-posed problem with surface microseismic data often exhibiting beach ball-looking amplitude distributions for high-quality events (e.g., Eisner et al, 2010;Diller et al, 2015), is challenging with data acquired by borehole arrays, their narrow-angle, irregular directional apertures can lead to instabilities in the estimated moment components and even to ambiguity in moment tensor inversion (MTI). One particular example of this ambiguity -MTI of data collected by a vertical receiver array placed in a horizontally layered isotropic or vertically transversely isotropic (VTI) mediumis well documented in the literature (e.g., Nolen-Hoeksema and Ruff, 2001;Vavryčuk, 2007;Baig and Urbancic, 2010;Eaton and Forouhideh, 2011;Song and Toksöz, 2011;Rodriguez et al, 2011;Staněk and Eisner, 2013).…”