The prediction of volumes, compressibilities and thermal expansion coefficients of hydrocarbon mixtures

Abstract

Accurate predictions of volumetric behavior for reservoir fluids are necessary for many calculations in petroleum engineering. The methods presented here employ the concept of residual quantities for prediction of volumetric behavior. An equation developed for methane predicts the molal volumes with an average absolute deviation of 0.15%, when applied to 442 PVT points. An equation developed for gaseous hydrocarbon mixtures predicts molal volumes with an average absolute deviation of 0.73% when applied to 264 natural gas and condensate systems including 2,043 PVT points. Another equation developed for liquid hydrocarbon mixtures predicts the molal volumes with an average absolute deviation of 1.12%, when applied to 346 crude oil systems including 1,759 PVT points. Both equations require composition of the mixture expressed as mole fraction of methane through heptanes-plus, nitrogen, carbon dioxide and hydrogen sulfide together with the characteristics of the heptanes-plus fraction, in order to calculate molal volume at the desired temperature and pressure. The equations cover wide ranges of the variables involved and their accuracy of prediction is considerably better than that of other available methods. The equations may be easily differentiated to calculate the coefficients of isothermal compressibility and the coefficients of isobaric thermal expansion.* Equations to calculate these quantities have been presented. *In the following, the coefficient of isothermal compressibility and the coefficient of isobaric thermal expansion will be referred as compressibility and thermal expansion coefficient, respectively.