Accurate phase equilibria predictions for hydrates of multi-component natural gases

The sour natural gas at higher temperatures and lower pressures readily forms hydrates and stays stable and hence are responsible for plugging and causing flow assurance related issues. Predictions of formation and dissociation conditions of these hydrates are necessary in applications for preventing such hazards primarily due to the blockages of pipelines. However, natural gases from the gas reservoirs can have combinations of different concentrations of each of the following constituents, CH4, C2H6, C 3H8, C4H10, N2, C0 2 and H2S. Presence of C02 and/ or H 2S in the natural gas leads to the corrosion of the offshore pipelie installations, which are difficult to access and fix. Presence of high concentrations of C02 and/ or H2S along with other components often found in natural gas, confines the accurate functioning of several of the available phase behavior models. The major limitation for their inaccuracy can be attributed to the association of C02 and H 2S in hydrate system. In the present work, a new thermodynamic computing approach is developed for predicting the phase equilibria for hydrates of multicomponent sour natural gases (with C02 and H2S) from different natural gas systems. The model of Chen and Guo is extended for multicomponent sour natural gas hydrate system using the Kihara potential functions to model the guest-host interaction energies. Adjacently, a semi-empirical form is proposed to calculate the equilibrium hydrate temperature for hydrates of natural gas with and without C02 and H2S. The developed model is fitted with experimental data on the phase equilibria of sour natural has hydrate system and found to be satisfactory. The average absolute deviation pressure percentage (AADP %) for most of the cases studied is observed to be well within 10%, thus proving its efficiency. The present model can, therefore, find prospective applications for developing mitigation techniques to address flow assurance issues as well as for robust natural gas and hydrate reservoir models containing sour gases. Copyright 2014, Offshore Technology Conference.