An Examination of the Ternary Methane + Carbon Dioxide + Water Phase Diagram using the SAFT-VR Approach

Abstract

In this work, the molecular based Variable Range Statistical Associating Fluid Theory (SAFT-VR) has been used to estimate the global phase equilibria diagram of the ternary mixture water + carbon dioxide + methane, over a wide pressure and temperature range. An accurate determination of the phase equilibria of this mixture is relevant in Petrophysics, as, for instance, in enhanced natural gas recovery from low permeability reservoirs (the so-called tight gas reservoirs), or in geology, as it is the basic composition of many geological fluids. A previous study on the phase behavior of the binary mixtures involved is presented, using in a transferable manner the characteristic molecular parameters for the three molecules involved. The ternary mixture presents a very rich and complex phase behavior, with a wide region of the thermodynamic space of phases (at higher pressures) presenting a large gap of ternary liquid-liquid equilibria, that upon descending pressures leads to the transition to a three-phase liquid-liquid-vapor equilibria region, and both regions are separated by a continuous critical end point line. The ability of the theory to describe this complex multicomponent mixture phase transition with a reduced and physically sound set of characteristic parameters must be underlined.

Calculation of vapor–liquid equilibrium and PVTx properties of geological fluid system with SAFT-LJ EOS including multi-polar contribution. Part III. Extension to water–light hydrocarbons systems

“…It is important to accurately describe the fluid phase equilibria of the water-hydrocarbon systems (i.e. the mutual solubilities of hydrocarbons and water) for the exploration of petroleum, natural gas and so-called nonconventional sources (such as gas hydrates, shale gas, and the tight gas reservoirs), for enhanced oil recovery, and for the design and operation of natural gas facilities, crude oil refineries, and petrochemical plants (Guillaume et al, 2001;Lin et al, 2007;Oliveira et al, 2007;Miguez et al, 2011). Understanding of the phase behavior of the water-hydrocarbon systems is also important for environmental purpose (Oliveira et al, 2007;Zoghi et al, 2011).…”

Experimental and Molecular Modeling Study of the Three-Phase Behavior of (n-Decane + Carbon Dioxide + Water) at Reservoir Conditions

“…We compare our experimental findings with the predictions of SAFT-VR. 37,38 We use this method as it has already been shown in a number of studies [67][68][69][72][73][74] to provide an accurate description of the phase behaviour of mixtures consisting of alkanes, CO 2 and water, for wide ranges of thermodynamic conditions. Finally, where possible, further comparisons with data for the binary subsystems are also presented.…”

Experimental and molecular modelling study of the three-phase behaviour of (propane+carbon dioxide+water) at reservoir conditions

“…We compare our experimental findings with the predictions of SAFT-VR [74,75]. We use this method as it has already been shown in a number of studies [4,66,68,69,71,72,[76][77][78] to provide an accurate description of the phase behaviour of mixtures consisting of alkanes, CO 2 and water, for wide ranges of thermodynamic conditions. Finally, where possible, the agreement or deviations from published binary experimental data are further studied to analyse the effect of adding a third component and a third coexisting phase in the phase equilibria of the system.…”

“…Certain challenges were highlighted in these systems, such as the difficulty of modelling mutual solubilities of phases of very different nature, as represented by large variations between the dielectric constant of each phase and/or dipole moment of the molecules. Previous attempts to model the phase behaviour of ternary systems of the type of interest here are again limited, but the work of Míguez et al [72] and Kontogeorgis et al [73] on the system (methane + carbon dioxide + water) are of relevance. Two different models are used in these works.…”

“…Two different models are used in these works. Míguez et al [72] use the SAFT-VR equation of state with a limited adjustment of cross interaction parameters to have a global estimation of the phase diagram, while in [73] the cubic plus association (CPA) equation of state is chosen along with a different interpretation of the unlike interactions between CO 2 and water, which are represented based on a cross-associating model.…”