Experiments and modeling of hydrate phase equilibrium of CH4/CO2/H2S/N2 quaternary sour gases in distilled water and methanol-water solutions

Preventing hydrate plugging is of great concern in the natural gas production and transportation industries. In this paper, hydrate formation conditions of three CH4/CO2/H2S/N2 sour gases with different H2S and CO2 contents in both distilled water and methanol-water solutions were measured. The temperature range was varied from 270.15 to 292.15 K, and three mass fractions (15 wt%, 20 wt% and 30 wt%) of methanol in methanol-water solutions were considered. The experimental results showed that the hydrate formation conditions of tested quaternary sour gases are related to the concentrations of gas components to a large extent, in which H2S played the most important role. The addition of methanol in water significantly increased the gas mixtures' hydrate formation pressures, in which the inhibiting effect of methanol on the hydrate formation pressures showed a nonlinear relation to its concentration in the aqueous solution. For simulating the hydrate formation of tested sour gases in distilled water, both the PVTSim and Chen-Guo model showed acceptable prediction precisions in water, but they did not perform well for the methanol-water mixtures. At the same time, a calculation method based on the original Chen-Guo model for predicting the hydrate formation conditions of CH4/CO2/H2S/N2 quaternary sour gases in methanol-water solutions was proposed in this work. The modeling results are in excellent agreement with the experimental data.