Multi-Phase Multi-Component Equilibrium Flash Calculations for CompFlow Bio using Modified Volume-Translated Peng- Robinson Equation of State

Abstract

Numerical modelling of fluid flow and transport in reservoir engineering problems is a challenging task, given variability and uncertainty in the physical properties of rock, the complexities of multi-fluid interaction at elevated pressure and temperature and limited computational resources. Nonetheless, this thesis seeks to provide a basis for expansion of our modeling capabilities in the context of hydrocarbon mixtures at equilibrium conditions. We briefly describe the numerical simulator CompFlow Bio and propose a package, with the solid thermodynamics background required for dealing with highly non-ideal mixture behavior, to amend this simulator. Herein we present the governing equations of phase equilibrium and key expressions for calculating equilibrium mole fractions and phase properties over a broad range of pressure and temperature. We employed the traditional flash calculations model used in the petroleum industry and redesigned its procedure in order to accommodate the special design of CompFlow Bio and verify this modified model against a well-known commercial simulator results. In this proposed model, we use a modified Peng-Robinson equation of state improved by volume-translations for performing equilibrium flash calculations. Then, we describe three different case studies developed in order to investigate the accuracy of the proposed model, as well as describe the complexity of hydrocarbon mixture behavior at reservoir conditions. Our findings indicate that: our model’s performance is in close agreement with the commercial simulator software. Furthermore, these findings highlight various aspects of hydrocarbon behavior at high pressure and temperature, such as: decrease in non-aqueous phase mass density with increase in pressure while a gaseous phase is disappearing; a growing gas phase can dry out of the aqueous phase until it disappears; injection of carbon dioxide for enhanced oil recovery does not guarantee swelling of the non-aqueous phase and gas phase mass density increase with the injection of carbon dioxide, depending on the light hydrocarbon content of the gaseous phase.