Regular Article

CO₂ hydrate formation in NaCl systems and undersaturated aqueous solutions

¹ Hydrates, Flow Assurance & Phase Equilibria Research Group, Institute of GeoEnergy Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK
² Mines ParisTech, PSL University, CTP – Centre of Thermodynamics of Processes, 35 Rue Saint, Honoré 77305, Fontainebleau Cdex France
³ Equinor ASA, Arkitekt Ebbells veg 10, 7053 Ranheim, Trondheim, Norway

^* Corresponding author: a.chapoy@hw.ac.uk

Received: 26 September 2022
Accepted: 2 March 2023

Abstract

A high-pressure experimental setup was used to obtain experimental data on the Hydrate Equilibrium (melting) Temperature (HET) of aqueous phases undersaturated with CO₂, at different CO₂ saturation levels and with different aqueous phase compositions (sodium chloride and sodium chloride/calcium chloride). This paper details the experimental equipment, methods, test fluids, and results. To study the phase equilibria of CO₂-brine systems and further validate the results, hydrate dissociation conditions of CO₂ in different concentrations of NaCl aqueous solutions were measured in the low-temperature region and over a wide range of pressure. Experimental results were compared against predictions of the simplified Cubic Plus Association Equation of State (sCPA-EoS) coupled with the van der Waals and Platteeuw solid solution theory.