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Importance of Equations of State in Petroleum Engineering

O'Reilly, Daniel

Engineering Honours Degree 2007

University of Adelaide


Equations of State (EOS) are applied throughout many areas of the petroleum industry. Due to the narrowness and complexity of the field there is major shortage of engineers who have a thorough knowledge of EOS. This paper was written as a “ground up” introduction to the theory and application of EOS in the petroleum industry. Very little prior knowledge is required for readers who already have some familiarity with the industry. The paper may be read as an introduction to the field of EOS.

After a review of basic reservoir thermodynamics, the history and development of EOS are presented. The mathematical foundation of several popular equations is covered and simple numerical comparisons between equations are graphed to provide a feel for which equations are most accurate. Two popular EOS present in commercial PVT simulators are covered to provide up-to-date information on the field.

A new PVT simulation program was also developed by the author to educate readers on the theory behind EOS and its application to mixture thermodynamics. The program was very successful in simulating saturation pressures and critical properties for basic hydrocarbon mixtures. It was tested thoroughly against experimental data and commercial PVT packages. The majority of figures in this report were created using this simulator or a commercial counterpart – only a small number of figures originate from outside literature.

Acquisition of the input data required to run an EOS simulation has been covered in detail. This entails the necessary laboratory experiments and associated quality control measures for PVT data. Furthermore, the author has recognised the importance of EOS tuning in the industry, and presents several popular methods. It is widely known that an EOS should never be applied to a field before it has been properly tuned against experimental PVT data. Some example laboratory data has been successfully tuned by the author for illustration purposes.

Despite being very difficult to summarise in a short paper, some field applications of EOS have also been covered. An EOS can be used in a variety of situations in petroleum engineering, and some interesting examples from literature show this diversity. The importance these equations have in the petroleum industry has been summarised through many different means.

Australian School of Petroleum



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