CCS and Power Systems
Carbon Storage - Geologic Storage Technologies and Simulation and Risk Assessment
Area 1: Influence of Local Capillary Trapping on Containment System Effectiveness
Project No: FE0004956
Researchers at the University of Texas at Austin (UT) are conducting simulations and experiments to establish proof-of-feasibility of a novel concept for assessing capillary trapping in storage formation, as well as to confirm that storage formations have characteristic, spatially correlated distributions of transport properties. Local capillary trapping is an important mechanism for immobilization of CO2 in the subsurface. It occurs at scales from centimeters to tens-of-meters during buoyancy-driven movement of CO2 through heterogeneous storage formations. The distribution of transport properties may vary according to the geologic characteristics of each formation. Certain geologic structures within the formation can become local capillary traps for rising buoyant fluid (Figure 1). Project researchers are using numerical simulation and laboratory experiments to analyze the extent to which local traps fill with stored CO2, and are systematically determining the geologic controls on potential capillary trapping structures. This requires detailed characterization of the structure in a storage formation to assess its heterogeneity and complexity. UT Austin researchers are gathering key formation property data from technical literature and using these data in a suite of geostatistical models. Potential local capillary traps will be identified in the models from maps of their capillary entry pressures. Using this method to identify potential traps, UT will study the influence of the geologic setting (dip angle, maximum height of CO2 column) on potential trapping structures and establish a protocol for conducting buoyancy-driven fluid displacements with supercritical CO2 in heterogeneous, bench-scale porous media (Figure 2).
Once potential traps are identified, the researchers will attempt to quantify and upscale local capillary trapping (Figure 2) by (1) conduct bench-scale experiments in which the overlying seal is breached, demonstrating and potentially validating the buoyant phase fluid’s ability to escape from the local capillary traps; (2) determine the influence of CO2 injection operating conditions on local trap filling; and (3) examine the limitations of the filling of capillary traps by buoyancy dominated displacement. UT researchers will then simulate structural filling when CO2 emplacement occurs at a range of gravity numbers, corresponding to a range of injection rates, and will repeat these simulations with various volumes of CO2 added to the storage formation. After researchers establish the extent of capillary trap filling, they will quantify the extent of trapping capacity that persists after the overlying seal fails.
Figure 1. Capillary heterogeneity controls the structure of buoyancy-driven CO2 plume. Left: Schematic of plume re-direction by heterogeneity. Right: Concept is analogous to the spill point in an oil/gas trap.