Modeling Basin‐ and Plume‐Scale Processes of CO₂ Storage for Full‐Scale Deployment

Abstract

Integrated modeling of basin-and plume-scale processes induced by full-scale deployment of CO 2 storage was applied to the Mt. Simon aquifer in the Illinois Basin. A 3D mesh was generated with local refinement around 20 injection sites, with ~30 km spacing. A total annual injection rate of 100 Mt CO 2 over 50 years was employed. The CO 2 -brine flow at the plume scale and the single-phase flow at the basin scale were simulated. Simulation results show the overall shape of a CO 2 plume consisting of a typical gravity-override subplume in the bottom injection zone of high injectivity and a pyramid-shaped subplume in the overlying multilayered Mt. Simon, indicating the important role of a secondary seal with relatively low permeability and high entry capillary pressure. The secondary seal effect is manifested by retarded upward CO 2 migration as a result of multiple secondary seals, coupled with lateral preferential CO 2 viscous fingering through high-permeability layers. The plume width varies from 9.0 to 13.5 km at 200 years, indicating the slow CO 2 migration and no plume interference between storage sites. On the basin scale, pressure perturbations propagate quickly away from injection centers, interfere after less than a year, and eventually reach basin margins.The simulated pressure buildup of 35 bar in the injection area is not expected to affect caprock geomechanical integrity. Moderate pressure buildup is observed in Mt. Simon in northern Illinois. However, its impact on groundwater resources is less than the hydraulic drawdown induced by long-term extensive pumping from overlying freshwater aquifers.

On scale and magnitude of pressure build‐up induced by large‐scale geologic storage of CO2

“…In the other scenario, where a higher injection rate is assumed, the pressure buildup in the core injection area is a limiting factor for dynamic storage capacity, even when the pressure bleed-off effects are considered. In the base case, the contributions to accommodating the 5.43 km 3 resident brine displaced by free-phase and dissolved CO 2 at 50 years include (1) While these total volumes of fluid migration are large, they correspond to very small flow velocities and displacement lengths that would not cause environmental concerns 6 . For example, the average flow velocity across the lateral boundary of the model domain is less than 0.01 mm/year, and the maximum rate of fluid migration through the caprock is only 0.65 mm/year.…”

“…In the latter, the injection time could be increased up to 1200 years while keeping the fractional pressure buildup lower than the regulated value. (This calculation is based on a linear correlation between pressure buildup and log(t) at later time; see Figure 9a in Zhou et al 6 .) This leads to a dynamic storage capacity close to the upper bound of the static storage capacity.…”

“…The relevant physical processes include (1) lateral propagation of pressure buildup within the storage formation away from injection sites to the margins of a sedimentary basin, (2) attenuation of pressure buildup caused by basinscale migration of resident brine into and through the caprock and basement rock, (3) superposition of pressure buildup from neighboring injection sites 6 , and (4) boundary effects at basin margins. Such boundary effects are apparent in a closed or partially closed storage system 3,15 .…”

“…The pressure buildup (as well as CO 2 plume evolution) was simulated numerically based on detailed site characterization data. The first study considered a hypothetical future full-scale deployment scenario in the Mount Simon Sandstone in the Illinois Basin, which represents a laterally extensive open system [5][6] . The second case study involved CO 2 storage in the partially compartmentalized Vedder Sand in the southern San Joaquin Basin in California 15,20 .…”

“…Recent modeling studies on open systems have indicated that the storage capacity for CO 2 may be limited by pressure effects in response to the injection and storage of additional fluid volumes, because the pressure buildup in a storage formation cannot exceed a maximum tolerable pressure gradient that would assure geomechanical integrity of the caprock [4][5][6] . Brine migration through localized pathways (e.g., leaky faults and wells) driven by elevated pressure may degrade shallower groundwater resources, further limiting effective storage capacity.…”