Effects of rate law formulation on predicting CO2sequestration in sandstone formations

Abstract

Injection of CO2 into confined geological formations, given their massive carbon storage capacity and widespread geographic distribution, represents one of the most promising options for CO2 sequestration. Reactive transport models have been constructed to understand the process of carbon storage and predict the fate of injected CO2. Model results, however, differ dramatically because of the large uncertainties attributed to reaction kinetics. The root of this problem is partly related to the one of the biggest challenges in modern geochemistry: The persistent two to five orders of magnitude discrepancy between laboratory-measured and field-derived feldspar dissolution rates. Recently, advances in reaction kinetics research suggest that the slow precipitation of secondary minerals produces negative feedback in the dissolution–precipitation loop, which reduces the overall feldspar dissolution rates by orders of magnitude. In this study, we focused on how the coupling between feldspar dissolution and secondary mineral precipitation, as well as mineral carbonation, is affected by rate law uncertainties. Reactive transport models with four different rate law scenarios were used for CO2 sequestration in a sandstone formation resembling the Mt. Simon saline reservoir in the Midwest, USA. The results indicate that (1) long-term mineral trapping is more sensitive to rate laws for feldspar dissolution than to rate laws for carbonate mineral precipitation and (2) negligence of the sigmoidal shape of rate – ∆Gr relationships and the mitigating effects of secondary mineral precipitation can overestimate both the extent of feldspar dissolution during CO2 injection and in turn mineral trapping. Copyright © 2015 John Wiley & Sons, Ltd.