Acoustic Response of Brine Saturated Reservoir Rocks During Injection of Supercritical Carbon Dioxide

M. Lebedev¹, V. Mikhaltsevitch¹, and B. Gurevich¹

Abstract

Quantitative knowledge of the acoustic response of rock from an injection site on supercritical CO₂ saturation is crucial for understanding the feasibility of time-lapse seismic monitoring of CO₂ plume migration. Ultrasonic experiments were conducted on CO₂ flooded sandstone core samples. The purposes of these laboratory tests were to investigate the effect of brine, liquid CO₂, supercritical CO₂ (scCO₂), and mixture of scCO₂ with brine, on the acoustic response of sandstones to provide an information of the sensitivity of time-lapse seismic (4D) imaging of the CO₂ plume. Samples were tested in a triaxial pressure cell at room and elevated temperatures; cell was equipped with core flooding equipment, and has an innovative arrangement of ultrasound transducers. The sandstone samples varied in porosities between 14 and 23% and permeabilities between 4 mD and 2.7 D. Independent control of confining and pore pressures, combined with temperature control allowed to simulate reservoir conditions insitu. Pore pressures and temperatures were varied from 4 MPa to 10 MPa, and 23°C to 45°C respectively to cover both vapour and supercritical regions of CO₂ phase diagram. Both compressional, P and shear waves, S were acquired at a range of effective pressures up to 60 MPa. An applicability of implementation of fluid substitution using Gassmann’s theory for has been proved in the experiments. Finally, more than 10% of decreasing of the compressional velocity during injection of scCO₂ into initially brine saturated samples was observed for some samples.

AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain