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

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).