Abstract

Determining the viability of, risks in, and optimal locations for sequestering CO₂ in the subsurface requires detailed knowledge of the complex interactions among CO₂, rock matrix, and pore fluids under appropriate in-situ pressure and temperature conditions. Many physical and chemical processes are known to occur both during and after geologic CO₂ injection, including diagenetic chemical reactions and associated permeability changes. Although it is commonly assumed that CO₂ sequestered in this way will ultimately become mineralized, the rates of these changes, including CO₂ hydration in brines, are known to be relatively slow. Together with hydrated CO₂, cations from brines may form solid-state carbonate minerals, ostensibly providing permanent sequestration.

Results of a series of laboratory CO₂-brine flow tests in rock core are being used to calibrate a recently coupled reactive transport simulator, TRANSTOUGH. TRANSTOUGH is a combination of the TOUGH2 simulator, for coupled groundwater/brine and heat flow, with the LANL chemistry code TRANS for chemically reactive transport. This paper presents laboratory test results and compares these to the model predictions. Variability in response among rock types suggests that CO₂ injection will induce ranges of transient and spatially dependent changes in intrinsic rock permeability and porosity. Determining the effect of matrix changes on CO₂ mobility is crucial in evaluating the efficacy and potential environmental implications of storing CO₂ in the subsurface.