FEASIBILITY OF CO2 SEQUESTRATION IN DEEP SALINE RESERVOIRS IN THE MIDWESTERN USA

An evaluation of hydrogeologic, geochemical, engineering, monitoring, and cost issues related to CO₂ sequestration in saline reservoirs is underway at Battelle with U.S. Department of Energy funding. The Mt. Simon Sandstone, a regionally extensive saline reservoir in the Midwest, is being evaluated as a potential host reservoir. The regional-scale sequestration capacity estimates based on formation thickness, depth, porosity, sand to shale ratio, and sweep efficiency show that the potential CO₂ storage capacity in the Mt. Simon Sandstone is sufficient for several decades of CO₂ emissions from the power plants in the region. These regional estimates however, do not account for local uncertainties in parameters such as thickness, depth, porosity, permeability, injection pressure, and seismic features that may have a greater influence on site-selection decisions and sequestration cost.

Local-scale hydrogeologic constraints on CO₂ disposal were evaluated using the University of Texas Compositional Simulator (UTCOMP) and data from active subsurface waste disposal facilities. The UTCOMP code was modified to account for environmental aspects of CO₂ sequestration such as solubility, dispersion, diffusion, and calculation of CO₂ mass balance. The radial model simulations conducted for several locations show that the variations in formation thickness and permeability in the region have a significant impact on injectivity of CO₂ and thus the feasibility of sequestration in the reservoir.

The simulations also calculate the mass of CO₂ dissolved in the brine over time. The dissolved CO₂ becomes available for geochemical reactions and possible permanent sequestration in solid phase. A large number of laboratory experiments were conducted at high pressure to evaluate the potential geochemical reactions. These experiments and the geochemical simulations showed that in general the CO₂ injection is compatible with formation brines and minerals and that there are no potential adverse reactions between these media.

The project also included a preliminary assessment of the potential for induced seismicity due to deep well injection of CO₂. In addition, an engineering and economic assessment to determine the costs associated with CO₂ capture, transport, injection, and monitoring was conducted.