Improving Point-Sensor Image Resolution with Distributed Acoustic Sensing at Brady's Enhanced Geothermal System

Abstract

To date, investigations into the deployment and ability of surface horizontal distributed acoustic sensing (DAS) fiber to characterize reservoirs has been lacking compared to borehole DAS configurations, which has been more prevalent for well diagnostics and vertical seismic profiles. Existence of three-component (3C) geophones and surface DAS fiber at Brady's enhanced geothermal system motivates this study. We review principles of compressional wave (P-wave) and shear wave (S-waves; SV and SH) particle motion and how these waves are recorded on horizontal DAS fiber as a function of their emergent angle. Note that vertical (P-wave) and orthogonal horizontal (S-wave) vibrators were used at Brady's making the consideration of S-waves potentially important. We then use elastic synthetic prestack modeling and prestack elastic Reverse-Time-Migration (RTM) to explore the joint use of geophone and DAS data for subsurface seismic imaging. In particular, we use different combinations of the geophone and DAS data as input to RTM, and then document the extent to which the Brady fault model geometry is recovered by the imaging. The migrated images demonstrate that surface DAS can improve imaging resolution over that obtained from sparse geophones alone.