Passive seismic multicomponent imaging using geometrical optics theory

Abstract

Here, a method of passive seismic imaging using multicomponent (3-C) data is presented. It is a Beamforming/Kirchhoff type migration, which is based upon the isotropic elastic wave equation within geometrical optics theory. To account for the effects of the source mechanism, polarity corrections are applied. Mathematically, the goal in a passive seismic survey is to characterize the source term in elastic wave equation, given seismic velocities and measured displacements at some number of observation points. Following Haldorsen et al. (2013) approach, using Helmholtz decomposition (Muller, 2007), the source wavefield can be decomposed into a curl-free longitudinal component (L) and divergence-free transverse (T) components. They are utilized to locate and characterize the seismic event that sourced the wavefield. The method can be implemented for both surface and downhole receiver array geometries. Here we are presenting the method as it applies to downhole surveys. Both the synthetic and field data examples are demonstrated. The synthetic example proves feasibility of the imaging technique, by producing the resulting image exactly in the place of the modeled synthetic event. We also confirm the accuracy of the approach with a real world example where the validity of the results are confirmed by quality-control of the steps of the imaging procedure, by the relative position to a treatment well of the event locations, and by the match of the imaged perforation shot to its known location.

3D passive wavefield imaging using the energy norm

“…Different imaging conditions acting directly on the wavefield displacement have been proposed for estimating the source locations in passive wavefield imaging (Steiner et al, 2008;Jeremic et al, 2015). For instance, Steiner et al (2008) propose to use the absolute value of the particle velocity, i.e., the time derivative of the displacement vector field, whereas Saenger (2011) presents an imaging condition based on the product between the stress and strain fields.…”