Continuum scale modelling of salt precipitation in the context of CO2 storage in saline aquifers with MRST compositional

Abstract

Carbon capture and storage (CCS) would contribute considerably towards climate change mitigation, if it would be implemented on a very large scale; at many storage sites with substantial injection rates. Achieving high injection rates in deep saline aquifers requires a detailed assessment of injectivity performance and evaluation of the processes that alter the permeability of the near-well region. One of the most common forms of the injectivity loss in the context of CO2 storage in saline aquifers is salt precipitation driven by the evaporation of brine into the relatively dry injected CO2 stream. We present a novel compositional transport formulation based on overall-composition variables which models salt as a separate solid phase which could potentially form through two essentially different ways, i.e., kinetic or equilibrium. To model formation drying-out and subsequent halite-precipitation, an accurate and reliable fluid model ePC-SAFT, which can effectively account for ionic effects, is applied. In addition, a volume balance approach (i.e., depending on how far the salt saturation is from the solubility limit) is implemented to estimate solid saturation in a simulation cell. The resulting simulator is benchmarked against several well-known examples, with analytical solutions demonstrating the ability of the code to cover a variety of physical mechanisms. Finally, injection of dry CO2 into a brine-saturated core-scale domain is simulated and sensitivity analyses over various parameters are performed. We show that the new model is capable to quantitatively represent the physics of salt precipitation (for example salt self-enhancing) under different reservoir conditions.