Evaluating Constant Volume Depletion Data

This paper presents results of analyzing constant volume depletion data obtained from experimental analyses of gas condensates and volatile oils. Theoretical and practical developments are supported by analyses of experimental data from two North Sea condensate reservoirs. The three major contributions of this work are: (1) presentation of material balance equations used to calculate fluid (particularly liquid) properties from measured constant volume depletion data, (2) a simple method for calculating "black oil" formation volume factors and solution gas-oil ratios for volatile systems using material balance results and a separator flash program, and (3) investigation of the Peng-Robinson equation of state as a tool for matching measured PVT data and studying vapor-liquid equilibria phenomena during constant volume depletion. The main example presented is a rich gas condensate whose measured, calculated and simulated phase behavior are fully documented in tables and figures. Complete description of the heptanes-plus fraction is also included so that other engineers can check, modify and hopefully improve fluid characterization using the Peng-Robinson (or any other) equation of state.