A double-process hydrate initiation mechanism is proposed for gas hydrate formation: ①?a quasi-chemical reaction process to form basic hydrate and ② an adsorption process of smaller gas molecules in linked cavities existing in basic hydrate

causing the entire hydrate nonstoichiometric. Based on this new mechanism

a thermodynamic model has been developed. Extensive test results indicate that the new model is superior to the traditional van der Waals-Platteeuw typed models and adequate for predicting the hydrate formation conditions even for complex fluid mixtures

such as natural gas

gas condensate and crude oil.