Experimental Studies on Seismic Monitoring of CO₂ in Geological Sequestration

Abstract

Laboratory experiments were conducted to measure P-wave velocity and deformation strain changes during injection of CO₂ into water-saturated Tako sandstone. The rock sample was cylindrical, with its axial parallel to the bedding plane, and fluids of water and CO₂ were injected from bottom end of the sample. P-wave velocity changes caused by CO₂ injection are typically about -10%, and -16% for the injection of supercritical CO₂. Such changes in velocity show that the seismic monitoring method is useful in mapping CO₂ movement in aquifers. Strain measured normal to the bedding plane was greater than that parallel to the bedding plane during CO₂ injection. In the case of supercritical CO₂ injection, bedding plane showed a strong effect on strain measurement. Such strain changes suggest the possibility of monitoring rock mass deformation by using borehole tiltmeters at geological sequestration sites.