Phase-Behavior Study of Hydrocarbon/Water/Methanol Mixtures at Reservoir Conditions

This paper presents a study of gas/condensate hydrocarbon mixtures and the effect of water, methanol, and isopropanol on their phase behavior. Only sparse data are available on the phase behavior of hydrocarbon/water/methanol mixtures at the high temperatures typical of these reservoirs. Such data are needed for compositional reservoir simulations of well treatments to optimize the performance of solvent treatments of blocked wells. Constant-composition expansion (CCE) experiments were performed to measure the phase behavior of hydrocarbon/water/methanol mixtures up to 300 F. The effects of temperature, pressure, and water and methanol concentration on the phase behavior were measured. The Peng-Robinson equation of state (EOS) was used to model hydrocarbon/water/methanol mixtures. The binary interaction parameters were tuned to fit the data and were found to show a linear variation with temperature. The binary interaction parameters and temperature-dependent volume-shift parameters are the key parameters to model these complex polar mixtures. Both the classical van der Waals and the Huron-Vidal (Huron and Vidal 1979) mixing rules were used and were found to give good agreement with the data. Phase-behavior experiments performed on hydrocarbon/water/isopropanol mixtures showed that isopropanol decreases the aqueous-phase volume fraction and increases the liquid-hydrocarbon-phase volume fraction compared with the analogous hydrocarbon/water/methanol mixtures. These data are needed to predict the conditions under which methanol/isopropanol treatments can be applied successfully in gas wells to remove water and condensate blockage.