Hydrologic and Elastic Properties of CO2 Injected Rock at Various Reservoir Conditions: Insights into Quantitative Monitoring of Injected CO2

Abstract

We calculated CO2 displacements in 3D natural sandstone (digital rock model) under various reservoir conditions using two-phase lattice Boltzmann (LB) simulations, and characterized the influence of reservoir conditions upon CO2 - water flow. The results of LB simulations under >50 conditions were used to classify the resulting two-phase flow behaviors into typical fluid displacement patterns on the diagram of capillary number (Ca) and viscosity ratio of the CO2 and water (M). In addition, the saturation of CO2 (nonwetting phase) was calculated and mapped on the Ca–M diagram. These results demonstrated that CO2 saturation is controlled by Ca and M, and the optimum CO2 saturation scales with Ca and M. When we applied similar analysis to the different type of rock, we found that CO2 saturation and behaviors are significantly different. These important differences could be due to the heterogeneity of pore geometry in the natural rock and differences in pore connectivity. By quantifying CO2 behavior in the target reservoir rock under various conditions (i.e., saturation mapping on the Ca-M diagram), our approach provides useful information for investigating suitable reservoir conditions for effective CO2 storage (e.g., high CO2 saturation). We further calculated seismic velocity of the digital rocks with injected CO2 under various reservoir conditions (e.g., Ca and M) using dynamic wave propagation simulation. By using the relation between seismic velocity and CO2 saturation parameterized by reservoir conditions, we could quantify in situ CO2 saturation in reservoir from monitoring data (seismic velocity).