Browsing by Author "Liu, Xuejian"

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    Understanding Subsurface Fracture Evolution Dynamics Using Time-Lapse Full Waveform Inversion of Continuous Active-Source Seismic Monitoring Data
    (Wiley, 2023) Liu, Xuejian; Zhu, Tieyuan; Ajo-Franklin, Jonathan
    Predicting the behavior, geometry, and flow properties of subsurface fractures remains a challenging problem. Seismic models that can characterize fractures usually suffer from low spatiotemporal resolution. Here, we develop a correlative double-difference time-lapse full waveform inversion of continuous active source seismic monitoring data for determining high-spatiotemporal-resolution time-lapse Vp models of in-situ fracture evolution at a shallow contamination site in Wyoming, USA. Assisted by rock physics modeling, we find that (a) rapidly increasing pore pressure initializes and grows the fracture, increasing the porosity slightly (from ∼13.7% to ∼14.6%) in the tight clay formation, thus decreasing Vp (∼50 m/s); (b) the fluid injection continues decreasing Vp, likely through the introduction of gas bubbles in the injectate; and (c) final Vp reductions reach over ∼150 m/s due to a posited ∼4.5% gas saturation. Our results demonstrate that high-resolution Vp changes are indicative of mechanical and fluid changes within the fracture zone during hydrofracturing.