Comparative PVT Simulation: An Application to Australasian Fluid Samples

Abstract

Abstract This paper investigates the effectiveness of Equations of State (EOS) when used to simulate Pressure-Volume-Temperature (PVT) experiments. The phase behaviour and volumetrics of six EOS and three EOS modifications (9 models in total) has been examined using a newly developed package inside the MATLAB software. The simulator is an expandable system designed to compare different EOS and fluid characterisation schemes. Comparison will be made between the Soave-Redlich-Kwong (SRK), Peng-Robinson (PR), Adachi-Lu (AL), Patel-Teja (PT), Schmidt-Wenzel (SW) and Esmaeilzadeh-Roshanfekr (ER) EOS, for which the SRK, PR and ER equations optionally include published volumetric shift parameters. Local Australasian fluid samples are studied to illustrate strengths and weaknesses of different EOS, using several fluid types. It was found that the Esmaeilzadeh-Roshanfekr EOS is most accurate for predicting gas-condensate properties, while the original SRK and PR equations remain reliable for oil samples. The purpose of the study is twofold: (1) Increasingly companies are optimising experimental PVT studies by simulating subsequent experiments using EOS1,2, or they are using preliminary simulation to evaluate the need for further experiments. This is particularly true for multi-contact miscibility experiments such as the Rising Bubble Apparatus or slim-tube test, which are time-consuming and costly. Furthermore, (2) there is reason to believe that thermodynamic models which provide better representation of PVT experiments without matching will perform best after complete matching has occurred. Matching EOS simulation with experiment, known as tuning or regression, is used in industry before application in compositional simulation. Obviously, this is only possible if PVT studies are available.