Öl- und Gasforschung

Abstrakt

A Derivative-less Approach for Generating Phase Envelopes

Siddiqui F

Petroleum engineers are often interested in the phase envelope that describes the characteristics of the pore fluids. These phase envelopes are normally generated by conducting laboratory measurements involving expensive PVT equipment and trained personnel. By using an Equation of State (EOS) based computer model that requires some hydrocarbon composition data, these envelopes can be generated almost instantly. An algorithm for generating a complete phase envelope using computer modeling was proposed by Michelsen. His procedure, based on EOS modeling, may sometimes suffer from convergence issues, especially near the critical region. In addition, his procedure requires the partial derivatives of fugacity, which are often difficult to get. In this work a phase behavior model was developed that incorporates some modifications to Michelsen’s algorithm avoiding the need for calculating these derivatives, which in turn put fewer requirements on the data and computation. These modifications allowed running the model successfully for different hydrocarbon systems without any convergence issues. Because the new model does not have to deal with the partial derivatives of fugacity, it can work with any EOS based phase behavior model. The new method has been applied to three different reservoir fluids and shows an exact match with the phase envelope generated using commercial software.