Applications of Reduced Order Models for Groundwater Impacts Due to Leaking Brine or Carbon Dioxide

Abstract:

The National Risk Assessment Partnership has developed a suite of reduced-order models (ROMs) that can be used to predict the impact of CO₂ and brine leaks on overlying aquifers. The these computationally-efficient models are based on field-scale reactive transport simulations. The ROMs reproduce the ensemble behavior of large numbers of simulations very well and thus are well-suited to applications that consider a large number of scenarios such as sensitivity analysis, risk assessment, and uncertainty analysis. In this presentation, we seek to demonstrate applicability of ROM-based ensemble analysis. We consider two questions. First, what types of decisions could these analyses support? Second, what types of aquifers could these ROMs be applied to?

Four examples are presented for applying these ROMs, in ensemble mode, to supporting decisions in the early stages in a hypothetical geologic CO₂ sequestration project. These decisions pertain to site selection, site characterization, monitoring network evaluation, and health impacts. In all these cases, we consider potential brine/CO₂ leak rates at the base of the aquifer to be uncertain. We show that derived probabilities provide information relevant to the decision at hand.

Although the ROMs were developed using site-specific data from two aquifers (the High Plains, and the unconfined, carbonate portion of the Edwards), the models accept aquifer characteristics as variable inputs and so they may have more broad applicability. Of the nine water quality metrics the ROMs can predict (pH, TDS, 4 trace metals, 3 organic compounds) we conclude that pH and TDS predictions are the most transferable to other aquifers. Guidelines are presented for determining the aquifer types for which the ROMs should be applicable.