Thermodynamic properties of acid gas containing systems:: Literature review

The need for a description of the properties of mixtures containing acid gases with hydrocarbons and water is increasing. These needs are well identified in the field of acid gas injection, either for enhanced hydrocarbon recovery and/or for responding to environmental constraints. In particular, an improved knowledge of fluid mixtures (injected gas + hydrocarbons in place + aquifer) behaviour in the reservoir conditions is needed for the design of the process. In addition, the capability of these gases to form corrosive mixtures in aqueous solutions may have major consequences on the choice of the materials to be used. This paper presents the state of the art concerning the thermodynamic properties of such systems. In a first section, the available data, dealing with phase equilibria and volumetric properties, are reviewed Many low pressure binary data are available. However, few phase envelopes of real systems have been gathered, and in particular water dew point data. Moreover, while it is well known that systems containing CO2 can form liquid-liquid equilibria at moderate pressures, very few indications concerning such a behaviour with H2S exist. The second part of this paper deals with the models that are generally used for describing the phase behaviour of the above-mentioned systems. We conclude that cubic equations can describe correctly the systems not containing water. In the presence of water, however, the coupling of specific models for the hydrocarbon and the aqueous phase is needed.