PC Leary, PE Malin, PA Geiser, and CJ Sicking –-- September 2023 Two spectral and coda wave empirics of seismic background wavefields recorded by 1.5-2.5km deep sensors at Enhanced Geothermal System (EGS) microseismicity (Meq) stimulation projects are key to understanding surface seismic sensor imaging of ambient crust fluid flow structures. First, deep crustal stimulation Meq processes generate hHz-kHz wavefields that are not directly visible on standard surface seismic sensors. Second, multi-scale seismic scattering of primary hHz-kHz wavefields generates persistent semi-coherent ascending daHz background wavefields that do register on surface seismic sensors. The hHz-kHz deep background wavefields are coherent across sensors to 40-50m offsets, while the deep background daHz wavefields are coherent across 300-400m sensor offsets. Multi-scale seismic scattering coda wave amplitude decline empirics and the spatial correlation empirics of stimulation Meqs are consistent with the ambient crust power-law-scaling poro-permeability κ(x,y,z) ~ exp(αφ(x,y,z)) distributions given by pink-noise porosity φ(x,y,z) with poro-connectivity parameter α values that render κ(x,y,z) lognormal. Further, the coda wave amplitude declines are congruent with the oil field production flow decline analysis introduced by Arps. Our deep sensor background wavefield empirics demonstrate that stimulation Meq event hHz-kHz wavefields invisible to surface sensors grade into ascending background daHz wavefields visible to surface seismic sensors. The physical connection between stimulation Meqs and ambient crust poro-permeability structures allows stimulation Meq residual daHz wavefields recorded on surface sensor arrays to be processed into maps of subsurface crustal flow structures at 20-40 m spatial resolution as fixed by deep sensor hHz-kHz wavefield cross-sensor coherence. Surface seismic flow structure maps of convective geothermal flow systems will enable tracking of EGS stimulation flow enhancement and practical production well targeting for improved drilling efficiency in convective geothermal resource development. We end our presentation with a demonstration of ambient seismic imaging at the Newberry Geothermal Field.

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