CO2 hydrate saturation, permeability and injectivity in the saline environments

Abstract

In depleted or low-pressure subsurface reservoirs, the formation of CO₂ hydrate at low temperatures, induced by vaporization and isenthalpic expansion during dense CO₂ injection, can significantly impair well injectivity. The formation of CO₂ hydrates is governed by multiple factors, including CO₂ availability and its solubility, the properties of the surrounding fluids, and the characteristics of the rock. A key parameter influencing water activity and CO₂ solubility is the salinity of in-situ brine, which affects both the thermodynamics and kinetics of hydrate formation. The impact of salinity varies with the type and concentration of dissolved salts. This study investigates the impacts of two prevalent formation water salts, NaCl and CaCl₂ on CO₂ hydrate induction time, hydrate saturation, rock permeability reduction, and their implications for CO₂ injectivity. Coreflood experiments were performed under dynamic flow conditions, supplemented by computed tomography (CT) scanning to provide in-situ saturation profiles. The primary aim is to establish a correlation between the aforementioned parameters and mean ionic activity, thereby facilitating a generalized application of the results irrespective of the specific salt type. Empirical results indicate a marginally extended induction period at elevated initial salinity levels. Furthermore, an increase in mean ionic activity correlates with a decrease in hydrate saturation, which consequently leads to less significant reductions in permeability and injectivity.