Gas pressure depletion and seismicity

New study published in Geology

GEOLOGICAL SOCIETY OF AMERICA

Research News

 

IMAGE: A SECTIONED QUARTZ-QUARTZ GRAIN CONTACT REVEALING A THIN CLAY FILM (RIBBON-LIKE STRUCTURE). COMPACTION AND SHEAR OF THESE THIN CLAY FILMS HAS PLAYED A KEY ROLE IN CONTROLLING COMPACTION OF THE... view more 

CREDIT: MICROSTRUCTURES WERE OBTAINED BY B.A. VERBERNE.

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.

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FEATURED ARTICLE
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

Paper URL:
https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G48243.1/593344/Drill-core-from-seismically-active-sandstone-gas

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CAPTION

Idealized volume of reservoir sandstone undergoing vertical compaction with zero horizontal strain, typical of producing gas reservoirs. Note, in this simplification, all grain surfaces are coated with uniform clay films. In a real sandstone reservoir, clay films are discontinuous and locally absent, especially in distal regions of the field (orange--load-supporting quartz framework; blue--sparse feldspar grains; red--clay films).

CREDIT

The conceptual model was developed by B.A. Verberne, S. Hangx, and C. Spiers.

USAGE RESTRICTIONS

Credit B.A. Verberne, S. Hangx, and C. Spiers.