Investigating the Influence of Geological Heterogeneity on Capillary Trapping of Buoyant CO2 Using Transmitted-light Flow Visualization Experiments

Abstract

Small scale heterogeneity characteristic of clastic formations has been well known to affect CO2 migration pathways during geologic carbon sequestration. Especially far field from the injection sites, when buoyancy and capillary forces take over from the injection pressure gradients, the effects of such geological features on the CO2 plume movement become compounded. Numerical simulations have established that accumulation and trapping of the buoyant plume is primarily due to the contrast in capillary entry pressures of different rock layers. Capillary trapping can help maximize the storage capacity of reservoirs and hence it is essential to understand the dynamics of CO2 movement and trapping under the influence of small scale heterogeneity and quantify its effects. In this work we propose buoyancy driven migration experiments and simulations conducted at the meter scale using glass beads packed in a quasi 2D glass cell. Using a combination of two linear axis actuators, we demonstrate an automated glass bead filler system that can generate 2D heterogeneous structures in a reproducible manner. A fluid pair that mimics the phase densities and viscosities of CO2-Brine at reservoir pressures and temperatures is employed. Light transmission technique is used for visualization, and to calibrate and quantify saturation of the trapped non-wetting fluid during the experiments. Invasion Percolation is used to simulate the buoyancy driven flow. With the ability to generate different types of heterogeneous structures in a reproducible manner, and by comparing experiments and simulations, a systematic investigation of the effect of heterogeneity on capillary trapping becomes possible.