From CO₂ Transportation in Pipelines to Storage in Geological Formations: The Whole Picture of a Carbon Capture and Storage (CCS) Process with Chemical Thermodynamics

The aim of this study is to illustrate how brine composition could affect the CO2 solubility in the aqueous phase (which could affect the performance of installed flow meters on the pipelines), geochemical trapping mechanisms, and rock-fluid interactions and induced pore structure alteration of the host rock. This will be achieved through a combination of thermodynamic modelling and experimental work on reservoir rock dissolution owing to solubility of CO2 in brine and resulted pH variations. Herein, we have described and evaluated different equations of state (EoS) which utilise robust thermodynamic basis for demonstrating the solubility of gas species in the aqueous phase and integrated with Pitzer’s theory for determination of the activity coefficients of the ionic species involved. This methodology proved to be able to describe the chemical equilibria of the ionic species in the aqueous phase under HPHT conditions and in systems of interest with presence of gas, which can lead to rock dissolution phenomenon through rock-acidic fluid interactions. Generally, good agreements between predictions and experimental results are observed, and the thermodynamic modelling results could explain one of the dominating drivers of the rock dissolution phenomenon, which is pH alteration.