Author(s)

Marte Gutierrez, Daisuke Katsuki, Abdulhadi Almrabat

Civil and Environmental Engineering Colorado School of Mines, St. Golden, USA.

Geological sequestration (GS) of carbon dioxide (CO₂) is considered as one of the most promising technologies to reduce the amount of anthropogenic CO₂ emission in the atmosphere. To ensure success of CO₂ GS, monitoring is essential on ascertaining movement, volumes and locations of injected CO2 in the sequestration reservoir. One technique is to use time-lapsed seismic survey mapping to provide spatial distribution of seismic wave velocity as an indicator of CO₂ migration and volumes in a storage reservoir with time. To examine the use of time-lapsed seismic survey mapping as a monitoring tool for CO₂ sequestration, this paper presents mathematical and experimental studies of the effects of supercritical CO₂ injection on the seismic velocity of sandstone initially saturated with saline water. The mathematical model is based on poroelasticity theory, particularly the application of the Biot-Gassmann substitution theory in the modeling of the acoustic velocity of porous rocks containing two-phase immiscible pore fluids. The experimental study uses a high pressure and high temperature triaxial cell to clarify the seismic response of a sample of Berea sandstone to supercritical CO₂ injection under deep saline aquifer conditions. Measured ultrasonic wave velocity changes during CO₂ injection in the sandstone sample show the effects of pore fluid distribution in the seismic velocity of porous rocks. CO₂ injection was shown to decrease the P-wave velocity with increasing CO₂ saturation whereas the S-wave velocity was almost constant. The results confirm that the Biot-Gassmann theory can be used to model the changes in the acoustic P-wave velocity of sandstone containing different mixtures of supercritical CO₂ and saline water provided the distribution of the two fluids in the sandstone pore space is accounted for in the calculation of the pore fluid bulk modulus. The empirical relation of Brie et al. for the bulk modulus of mixtures of two-phase immiscible fluids, in combination with the Biot-Gassmann theory, was found to satisfactorily represent the pore-fluid dependent acoustic P-wave velocity of sandstone.

Biot-Gassmann Theory; CO₂ Geological Sequestration; Poroelasticity; Porous Rocks; Two-Phase Fluid Flow; Seismic Velocity

M. Gutierrez, D. Katsuki and A. Almrabat, "Effects of CO₂ Injection on the Seismic Velocity of Sandstone Saturated with Saline Water," International Journal of Geosciences, Vol. 3 No. 5A, 2012, pp. 908-917. doi: 10.4236/ijg.2012.325093.