Deep saline aquifers have been identified as highly promising reservoirs for geological storage of carbon dioxide as the end stage of carbon capture and storage operations. In order to design safe, effective and efficient storage processes and to predict the long-term fate of injected CO2, it is necessary to have a good quantitative understanding of a host of thermophysical properties of CO2 and, importantly, its mixtures with the host formation fluids and minerals. The thermophysical properties of interest include those controlling diffusive mass transfer between CO2- and brine-rich phase (principally mutual solubility and diffusion coefficients), those controlling convective mass transfer (principally viscosity and density) and those controlling capillary pressure (principally interfacial tension and contact angle). The effects on impurities that may be present in the CO2 stream is also an important factor.
In this contribution, I will summarise recent results and review the current state of knowledge related to interfacial properties of CO2-brine-mineral systems with and without diluent-gas impurities [1-3]. A large body of experimental fluid-fluid interfacial-tension (IFT) data have been gathered for CO2-brine systems at temperatures up to 448 K and pressures up to 50 MPa with a wide range of brine chemistry [4, 5]. The effects of diluent gases have been studied in CO2-diluent-water systems over similar ranges of temperature and pressure with argon, nitrogen and hydrogen as the diluent. Furthermore, contact angles on pure calcite have been measured for a CO2-brine system and the results show water-wet behaviour but with regions of mixed wettability. The experimental challenges of these measurements are manifold. Modelling of the interfacial properties also presents significant challenges. Results will be discussed from the application of gradient theory, with the SAFT-VR Mie equation of state, to the IFT of CO2-diluent-water systems. This approach is quite successful but has not yet been extended to brine systems. On the other hand, a simple but effective empirical correlation has been developed for the IFT of CO2-brine systems, covering a wide range of brine chemistry, although this has not yet been extended to include the effects of diluents.
References
[1] A. Georgiadis, G. Maitland, J.P.M. Trusler, A. Bismarck. J. Chem. Eng. Data, 55 (2010) 4168-4175.
[2] X. Li, E. Boek, G.C. Maitland, J.P.M. Trusler. J. Chem. Eng. Data, 57 (2012) 1078-1088.
[3] X. Li, E.S. Boek, G.C. Maitland, J.P.M. Trusler. J. Chem. Eng. Data, 57 (2012) 1369-1375.
[4] Y.T.F. Chow, D.K. Eriksen, A. Galindo, A.J. Haslam, G. Jackson, G.C. Maitland, J.P.M. Trusler. Fluid Phase Equilib., 407 (2016) 159-176.
[5] Y.T.F. Chow, G.C. Maitland, J.P.M. Trusler. J. Chem. Thermodyn., 93 (2016) 392-403.
