Unravelling wave-velocity and electrical resistivity changes during core flooding experiments on Berea sandstone using in situ micro-CT imaging

Griffiths, L., Soldal, M., Marín-Moreno, H., Park, J., Victor, R.A., Ramos, E. R.F., Menezes, P.T.L., Correa, J.L. and Mane, M.A. (2021) Unravelling wave-velocity and electrical resistivity changes during core flooding experiments on Berea sandstone using in situ micro-CT imaging. In Proceedings of the 55th U.S. Rock Mechanics / Geomechanics Symposium 2021. vol. 5, American Rock Mechanics Association. pp. 3453-3459 .

Abstract

We present electrical resistivity and elastic wave velocities in the axial and radial directions, and static bulk modulus data from three core flooding experiments on Berea Buff sandstone samples. Two experiments involved injecting brine into an oil saturated sample. One of these was performed within a micro-CT scanner to image the fluid front and calculate the fluid saturation throughout the sample volume. The third experiment involved injecting oil into a brine saturated sample. In the brine-into-oil experiments, we observe a flat front of brine migrating upward with a constant velocity and reaching a final brine saturation of around 42 %. Both static and dynamic moduli decrease with volume of injected brine, beyond the values predicted by Gassmann poroelasticity theory. Our experimental data may be explained by a water weakening effect, represented by a saturation dependent reduction in dynamic shear modulus. Our results highlight the sensitivity of electrical resistivity for geophysical monitoring during injection of a conductive fluid into a formation filled with an insulating fluid (as for Enhanced Oil Recovery - EOR). For seismic monitoring, we recommend that water weakening should be accounted for when estimating brine saturation and the geomechanical response to EOR.

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Contributors

Author: H. Marín-Moreno

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