Continuous seismic monitoring of hydraulic fracturing reveals complex subsurface dynamics: observations using distributed acoustic sensing and surface orbital vibrators

Understanding hydraulic fracturing is crucial to improving the stimulation of unconventional reservoirs and increasing fluid production. This study proposes a novel seismic monitoring technology, using distributed acoustic sensing (DAS) and surface orbital vibrators (SOV), to capture fracture seismic response and mechanical properties at high temporal intervals. We analyze continuous time-lapse Vertical Seismic Profiling (VSP) data acquired every hour during the first nine days of treatment of an unconventional reservoir in the Austin Chalk/Eagle Ford Shale Laboratory. The VSP data contains clear seismic signals scattered from the activated fractures. The spatiotemporal changes of the fracture reflectivity revealed by the SOV/DAS data correlate well with the observations of fracture locations inferred from low-frequency DAS data. These results capture the fracture opening and closure processes, as well as highlighting potential pre-stage activations of the fractures due to hydraulic connectivity with pre-existing fracture systems. Therefore, analysis of the presented data set provides a unique opportunity to understand fracture initiation and subsequent evolution, not only in the context of unconventional resources, but also in enhanced geothermal systems.