Accurate Prediction of Dissociation Pressures of Natural Gas Hydrates Containing Carbon Dioxide and Hydrogen Sulfide for Efficient Flow Assurance Phenomena

摘要

Information on the phase behavior of gas hydrate is vital for several mitigation techniques to control their formation in pipelines and surface facilities for efficient flow assurance during the production and transportation of natural gas and reservoir fluids. The pipeline environment (high pressure and low temperature) favors the formation of natural gas hydrate, which is one of the main elements in the flow assurance issues and this has to be taken in to account very seriously. Depending upon the composition of the gas produced, hydrates can form different physical structures and thus require careful attention whole modeling their phase behavior. The better thermodynamic models are necessary to design and understand the phase behavior of produced trapped natural gas from natural gas hydrates from subsea environments. Most of the models available in an open literature are primarily applicable at relatively low pressure condition. In this work, model of Chen and Guo along with the three famous Equation of States (EoS), namely, Peng-Robinson (PR), Peng-Robinson-Stryjek-Vera (PRSV) and Soave-Redlich-Kwong (SRK), are used to model the hydrate phase behavior at high pressure conditions. Their efficacy to model phase behavior for hydrates of pure natural gases and gas mixture containing H2S and CO2 is presented and tested against the experimental data available from open literature at high pressures conditions. The developed model uses the published Lennard-Jones cell potentials of typical gas species that form hydrates assuming the adsorption would be carried out in the cavities of hydrate structures. We optimized the computed phase diagrams based on three EoS with experimental phase diagram data from literature and determined the model parameters with less percentage average deviation. The present papers discusses about modeling of the phase behavior of binary gas mixture hydrates like CH4-C2H6, CH4-CO2 and CH4-H2S. Model predictions are validated against the experimental data from the literature, and observed to be in well agreement for high pressure range which helps in the flow assurance. Such models shows potential of their application in understanding flow assurance phenomena at higher pressure.