Experimental procedure and results to measure the composition of gas hydrate, during crystallization and at equilibrium, from N2–CO2–CH4–C2H6–C3H8–C4H10 gas mixtures

Mixed Clathrate hydrates are an important issue in many fields, like flow assurance in the oil industry, as well as gas capture and storage, air conditioning, etc … Usually, studies of gas hydrates from hydrocarbon gas mixtures do not mention the volume of hydrate, nor the hydrate composition, and ternary or quaternary mixtures are not considered. Also, data involving propane and butane are limited. Therefore, we suggest both an experimental and modeling study of mixed clathrate hydrates from N2–CO2–CH4–C2H6–C3H8–C4H10 gas mixtures, in temperature range of [0.8–19 °C] and pressure range of [1.4–66 bars]. The experimental work provides 78 equilibrium points. Two procedures were used to perform crystallizations. The main procedure (71 equilibrium data) corresponds to a method at high crystallization rate (high supersaturation, or high ΔP). The first objective is to study the gas hydrates formation in usual dynamic conditions (start-up or reboot of an oil exploitation). The second method, 7 data, corresponds to a low rate of crystallization. This second objective is to investigate the impact of the speed of crystallization on the final equilibrium. For both procedures, P-T data are given, as well as the compositions of each phase at equilibrium. At last, thermodynamic modeling is used to compare the experimental results of both procedures. Kihara parameters of N2, CO2 and CH4 are taken from the literature, while parameters for C2H6 are regressed and given in this work. Results show a better agreement of the thermodynamic modeling with experimental study for pure gas hydrate and mixed gas hydrates at low crystallization rate. This observation suggests that mixed gas hydrates might form at thermodynamic equilibrium only at low crystallization rate.