Abstract: Under the conditions of higher pressure and lower temper-ature, the hydrate may be formed within the transporting pipe,wellbore, and multi-pore medium, when the nature gas contains some water, the gas hydrate will be dangerous for the produc-tion. Structures of hydrate have three types I, II and H. At
present, most hydrate theoretical prediction models have been developed based on the Vander Waals model. In this paper, based on the statistical thermodynamics, a new hydrate phase e-quilibrium model was derived. The new model is applied not on-ly to the prediction hydrate formation conditions for wellbore and transporting pipe, but also for the calculation of the phase
equilibrium of hydrate types I, II and H. It is proved that the model is good agreement with field data.

Key words: wellbore, pipeline, hydrate, phase equilibri-um theoretical model, prediction