Few, if any, blackoil-type correlations are available for describing the PVT behaviour of Gas Condensates and Volatile Oils. Such near-critical fluids are generally modelled using multi-component Equations of State (EoS). However, EoS require detailed laboratory analyses to be performed on actual reservoir fluids. For modelling production wells, this data is often of poor quality or not available at all.
In a production system, there is usually a regular measurement of the post-separator condensate and gas gravities (stock tank oil and gas) and the total Condensate-Gas-Ratio (CGR). In this study, this data was used to generate a four pseudo-component description that was then used with a conventional EoS to make predictions of fluid behaviour.
The basis for the selection of the four pseudo-components is discussed as is the calculation of the component mole fractions using the two stock tank gravities, the CGR and the additional constraint of the mole fractions summing to unity.
The EoS model was tuned to data obtained from a North Sea Gas Condensate well. The tuned model was then used with an appropriate flow correlation to successfully predict top hole conditions, having specified measured bottom hole conditions.