Temporal-Spatial Evolution of Anisotropic Rock Properties During Hydraulic Fracture Stimulations at the First EGS Collab Testbed

Abstract

The EGS Collab project acquired continuous active-source seismic monitoring (CASSM) data before, during, and after hydraulic stimulations at the first testbed at the depth of 4850 ft at the Sanford Underground Research Facility in Lead, South Dakota, for monitoring fracture creation and evolution. CASSM monitoring used 24 hydrophones, 18 accelerometers, and 17 dipole sources within four fracture-parallel wells and two orthogonal wells. 3D anisotropic traveltime tomography and anisotropic elastic-waveform inversion of the campaign cross-borehole seismic data show that the rock within the stimulation region is a heterogeneous horizontal transverse isotropic medium. We use these inversion results as the initial models and apply 3D anisotropic first-arrival traveltime tomography and 3D anisotropic elastic-waveform inversion to the CASSM data acquired after each stimulation in May, 2018 and December, 2018. We observe the temporal and spatial evolution of seismic velocities and anisotropic parameters caused by hydraulic fracture stimulations, showing the regions of rock alternation caused by hydraulic fracture stimulation.