Peng-Robinson Equation of State Predictions for Gas Condensate Before and After Lumping

Abstract

Gas condensate compositional simulation studies are conducted to evaluate gas and condensate reserves and make comparisons of production methods for the economic development of a reservoir. The data needed for the evaluation are dew point pressure, gas compressibility factor, liquid volume and produced gas. Hosein and Dawe showed that compositional analysis greater than Single Carbon Number 24 (SCN24) is required for accurate prediction of these data by a tuned Equation of State (EOS). However they did not demonstrate the accuracy of their tuning technique with lumped components which are applied when performing simulation studies to reduce cost and computer time involved. Simple and complex schemes for lumping of the SCN groups into less than 6 Multiple Carbon Number (MCN) groups have been devised. However there are currently no criteria for selecting the best lumping scheme that will give similar accuracy to using many SCN groups except by trial and error, or by algorithms designed to test a number of schemes and to select the best one. In this paper we have used Whitson’s lumping scheme which is in the form of a simple mathematical expression in comparison to other lumping schemes from the open literature. The tuning technique of Hosein and Dawe was applied and differences of less than ±4.0 % from tuned EOS predictions before and after lumping of the SCN groups were obtained. These results indicate that the tuning technique of Hosein and Dawe could be used to perform accurate simulation studies of lean and rich gas condensate systems using MCN groups lumped by the Whitson’s lumping scheme. Complex algorithms are not necessary to select an appropriate lumping scheme. Key words: Gas condensate; Equation of state; Predictions; Single carbon number; Lumping