A Study on Phase Behavior and its Application to Cryogenic Technologies for Treatment of High CO2 Gas Fields

Abstract

In Malaysia more than 13 Tscf of natural gas reserve remain undeveloped due to high carbon dioxide (CO2) content of up to 70 mole% (Darman & Harun, 2006). High CO2 content gas fields will have to be developed to meet gas demand in Malaysia despite the technical and economical challenges. Cryogenic technology has been identified to be the most suitable technology for offshore since it is capable of handling a wide range of CO2 content. However, proper phase behavior study should be undertaken as CO2 may freeze-out to become solid at certain cryogenic conditions. The objective of this study is to validate the prediction of commonly used Equation of State (EOS) models on the Vapor, Liquid & Solid Equilibrium (VLSE) of CO2 - hydrocarbon system against existing experimental data and to simulate cryogenic process to remove CO2 for offshore application. Primary focus is given to the accurate prediction of solid CO2 behavior using conventional EOS models. Based on the selected EOS model, a phase behavior study under cryogenic condition has been conducted on a gas field containing CO2 level up to 52 mole% in the wellstream. A process simulation model is developed based on Ryan Holmes and Controlled Freeze Zone#x2122; (CFZ#x2122;) processes. In this study various feed and process conditions were evaluated to determine the optimal removal of CO2 from the wellstream. The proper representation of the actual high CO2 gas reservoir VLSE phase behavior using the available EOS model is very important to avoid unnecessary facility problem for a cryogenic technology application. From this study, advanced Redlich-Kwong-Soave (RKSA) model is recommended to be used for high CO2 fluid characterization and simulation.