(496e) Numerical Estimates for CO2 Leakage through Geological Seals Considered for Saline Reservoir Sequestration of Carbon Dioxide

The U.S. Department of Energy (DOE) currently has several field and large-scale candidate demonstration sites for saline reservoir sequestration of CO₂. The DOE demonstration projects have a programmatic goal of achieving 99% storage permanence of injected CO₂ over 100 and 1,000 years. In order to ensure the permanence of injected CO₂, the physical and chemical properties of the geological seals overlying the storage formation have to be evaluated for their ability meet the programmatic objectives. The goal of this study is to determine allowable limits for CO₂ leakage through geological seals considered at eleven candidate sites using common reactive minerals, structural, and hydraulic properties relevant to assessing their ability to prevent leakage.

Common seal characteristics were used to generate several equally probable realizations of a geological seal used at candidate sites for saline sequestration. CO₂ leakages through the generated seals were modeled using numerical simulations of a governing equation of a one-dimensional vertical Advection-Dispersion-Reaction (ADR) contamination transport model in a stochastic framework. Probability distributions are assigned to each parameter within the ADR to account for uncertainty and inter-individual variability and were sampled randomly using Monte Carlo simulation. The range of kinetics rates modeled were of dominant mineral phases undergoing dissolution through an acid-mechanism, in order to represent extreme cases. Scale-dependent parameters, like transverse dispersivity, were defined using correlations for macrodispersion as a function of field scale. Sensitivity analysis used to identify variables that exert the greatest influence on the calculated leakage distribution. Tornado plots with regression coefficients were used to identify linear correlations between each input variable and estimated CO2 leakage.

The simulations are intended to provide estimates for the expected ranges of CO₂ leakage, their associated probability, and to identify critical parameters and leakage processes common to geological seals considered for saline CO₂ sequestration. The results lead to a better understanding of the physical and chemical factors contributing to uncertainty in predicted CO₂ leakage and can be used for further modeling the risk associated with this climate mitigation strategy. Initial results show predominant dependence on fracture and fault flow over matrix fluid flow and dissolution effects.