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Effect of CO2 on Rock Properties: Frio Crosswell Case Study
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Third EAGE Workshop on Rock Physics, Nov 2015, Volume 2015, p.1 - 6
Abstract
A time- and –space dependent rock physics model using the constant cement model is used to interpret velocity changes observed from the CO2 sequestration site of Frio (Texas, USA). For this site, classical, purely mechanical rock physics models cannot explain the observed changes in both P-wave and S-wave velocities, suggesting changes in the rock frame itself. We introduce a non-elastic factor in the model in the form of cement percent change. The strategy was to estimate changes in the dry-frame from shear-wave measurements given by crosswell traveltime tomography, as the shear moduli is independent of the nature of fluids. Our approach allows variation of cement percent both in time and space, which effectively explains the time-lapse changes observed at the injection well and away from it. The model suggests that a small amount of cement is removed at grain contacts, consistent with minute dissolution.