Experimental and modeling investigation of gas hydrate phase equilibrium for methane/propane/n-heptane (MPH) ternary hydrates

High-gravity associated gases (wet natural gases), which are liberated from the oil, can form sII clathrate hydrates and may be represented through methane/propane/heptane (MPH) mixtures. The hydrate equilibrium conditions of three ternary mixtures of MPH containing up to two percent of heptane are measured using the isochoric pressure searching method while the experimental apparatus calibrated against literature data for pure methane, pure propane, and a binary mixture of 0.90 of methane and propane. The results indicated that the hydrate phase boundary of wet natural gas mixtures mainly depended on its composition, where the content of heptane played a more important role than that of propane. A thermodynamic framework based on the van der Waals and Platteeuw model was used to predict the hydrate equilibrium condition of MPH mixtures. The proposed approach demonstrates a good fit with the commercial packages PVTsim, Multiflash, and CSMGem, producing an acceptable AARD% based on the experimental data and literature for this study.