Dependence of CO_2-brine interfacial tension on aquifer pressure,temperature and water salinity

摘要

The displacement of brine by CO_2 during CO_2 injection and migration,and the displacement of CO_2 by invading brine in the wake of migrating CO_2 depend on the interfacial tension of the CO_2-brine system. An extensive laboratory program was conducted for the measurement of the interfacial tension (IFT) between CO_2 and water or brine covering the ranges of 2 to 27 MPa pressure,36C to 125C temperature,and 0 to 334,000 mg/l water salinity. The laboratory experiments were conducted using the pendant drop method combined with the solution of the Laplace equation for capillarity for the profile of the brine drop in the CO_2-rich environment. The analysis of the results reveals that: 1) for conditions of constant temperature and water salinity,IFT decreases steeply with increasing pressure in the range PPc,with an asymptotic trend towards a constant value for high pressures; 2) for the same conditions of constant pressure and temperature,IFT increases with increasing water salinity,reflecting decreasing CO_2 solubility in brine as salinity increases; 3) IFT increases with increasing temperature for T>Tc,with an asymptotic trend towards a constant value for high temperatures. These results indicate that,in the case of CO_2 storage in deep saline aquifers,trapping of CO_2 at irreducible saturation,storage efficiency and safety,and the evolution of the plume of injected CO_2 depend on the in-situ conditions of pressure,temperature and water salinity through the effects that these primary variables have on the IFT between CO_2 and aquifer brine. In addition,it was found that the IFT of CO_2-brine systems correlates well with CO_2 solubility in brine,which also depends on the same primary variables of pressure,temperature and water salinity.