Measurements and Predictions of Gas Hydrate Phase Equilibria for CO₂-Rich Gas Mixtures

Gas hydrates are an ever-present concern in oil and gas production, as their undesirable formation results in flowline blockage, creating a significant operational loss and hazardous conditions. While the predictions of gas hydrate phase equilibria are mostly reliable, the data for hydrate phase equilibria in the literature are mostly limited under typical natural gas mixtures with a low CO2 content. Uncertainties in the predictions are significant when considering CO2-rich systems at high pressures and high concentrations of thermodynamic hydrate inhibitors (THIs). This study assesses the reliability and accuracy of hydrate dissociation conditions for CO2-rich gas mixtures in the presence of THIs with experimental measurements of hydrate dissociation and comparisons to prediction tools. Hydrate phase equilibria for four gas mixtures of CO2 + CH4 (20/80 and 80/20 mol %) and CO2 + CH4 + C3H8 (20/75/5 and 60/37/3 mol %) with monoethylene glycol and methanol were determined at pressures up to 50 MPa and compared with four different prediction tools: PVTsim, Multiflash, Hu-Lee-Sum (HLS) correlation, and the ice melting point method. Among the predictions, the HLS correlation and ice melting methods showed a higher prediction accuracy than that of PVTsim and Multiflash. Overall, the determination and predictions of the phase equilibria in the conditions in this study are significant for CO2-rich systems, applicable to many of the current fields rich in CO2 and suitable for applications such as CO2 transportation for reinjection into the reservoir for greenhouse gas abatement.