Reactive transport modeling is a powerful tool to understand coupling of hydrology and geochemistry. During modeling activities, multiple input parameters are either assumed or adjusted to generate output results. To understand and compare impacts of input parameters on the final results, sensitivity analysis is typically carried out. However, most of these analyses for reactive transport models are done around a local point in the overall parameter space, probably because of the delicate reaction network that is hard to maintain during numerous simulations required for analyzing sensitivities globally. In this study, a new global sensitivity analysis method, the distance-based generalized sensitivity analysis (DGSA) method, was developed for analyzing parameter sensitivities over the entire parameter space. This new method is applied to a reactive transport model that explores chemical reactions in shale matrices during hydraulic fracturing. This reactive transport model looks at alteration in shale matrices when contacted with a water-based hydraulic fracturing fluid. Key mineral reactions include calcite dissolution, pyrite oxidation, iron oxide precipitation, and barite formation. After the global sensitivity analysis, input parameters for the model are ranked with their importance in affecting output results, in our case, the amount of flow-blocking barite mineral scale. This DGSA method can be adapted to sensitivity analyses of any model that requires adjustment of multiple input parameters.

An efficient global sensitivity analysis method for a reactive transport model on shale-fluid interactions

ACS Spring 2022

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