Phase equilibria modelling of petroleum reservoir fluids containing water, hydrate inhibitors and electrolyte solutions

Abstract

Formation of gas hydrates can lead to serious operational, economic and safety problems in the petroleum industry due to potential blockage of oil and gas equipment. Thermodynamic inhibitors are widely used to reduce the risks associated with gas hydrate formation. Thus, accurate knowledge of hydrate phase equilibrium in the presence of inhibitors is crucial to avoid gas hydrate formation problems and to design/optimize production, transportation and processing facilities. The work presented in this thesis is the result of a study on the phase equilibria of petroleum reservoir fluids containing aqueous salt(s) and/or hydrate inhibitor(s) solutions. The incipient equilibrium methane and natural gas hydrate conditions in presence of salt(s) and/or thermodynamic inhibitor(s) have been experimentally obtained, in addition to experimental freezing point depression data for aqueous solution of methanol, ethanol, monoethylene glycol and single or mixed salt(s) aqueous solutions, are conducted. A statistical thermodynamic approach, with the Cubic-Plus-Association equation of state, has been employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. Predictions of the developed model have been validated against independent experimental data from the open literature and the data generated in this work. The predictions were found to agree well with the experimental data.