Boulder, Colo., USA: Europe's largest gas field, the Groningen field in the Netherlands, is widely known for induced subsidence and seismicity caused by gas pressure depletion and associated compaction of the sandstone reservoir. Whether compaction is elastic or partly inelastic, as implied by recent experiments, is key to forecasting system behavior and seismic hazard.
Bart Verberne and colleagues sought evidence for a role of inelastic deformation through comparative microstructural analysis of unique drill-core, recovered from the seismogenic center of the field in 2015, 50 years after gas production started, versus core recovered before production (1965). Quartz grain fracturing, crack healing, and stress-induced Dauphiné twinning are equally developed in the 2015 and 1965 cores, with the only measurable effect of gas production being enhanced microcracking of sparse K-feldspar grains in the 2015 core.
Interpreting these grains as strain markers, Verberne and colleagues suggest that reservoir compaction involves elastic strain plus inelastic compression of weak clay films within grain contacts.
Drill core from seismically active sandstone gas reservoir yields clues to internal deformation mechanisms
Berend A. Verberne; Suzanne J.T. Hangx; Ronald P.J. Pijnenburg; Maartje F. Hamers; Martyn R. Drury; Christopher J. Spiers
Utrecht University, Dept. of Earth Sciences, Utrecht.
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