Production characteristic investigation of the Class Ⅰ, Class Ⅱ and Class Ⅲ hydrate reservoirs developed by the depressurization and thermal stimulation combined method

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The production characteristics of Class Ⅰ, Class Ⅱ and Class Ⅲ hydrate reservoirs are systematically investigated and compared using the depressurization and thermal stimulation combined method, and the roles of the reservoir and operation parameters in the hydrate reservoir development are discussed. According to different reservoir conditions, three forms of the combined method are selected for study: the wellbore-heating-assisting depressurization method, the hot-water-flooding method and the wellbore heating with depressurization method. Under the conditions in this paper, the results show the following: (1) For the Class Ⅰ hydrate reservoir, the gas production rate is high in the early period, during which most gas is produced; for the Class Ⅱ hydrate reservoir, the gas production rate maintains high throughout the entire production period; for the Class Ⅲ hydrate reservoir, the gas production rate periodically varied. (2) From the production view (gas recovery percent and hydrate dissociation percent), the Class Ⅱ hydrate reservoir is more favorable for development than the Class Ⅰ and Class Ⅲ hydrate reservoirs; from the economic view (energy ratio), the Class Ⅰ hydrate reservoir is better than the Class Ⅱ and Class Ⅲ hydrate reservoirs. (3) In the combined method, thermal stimulation plays an increasingly important role from Class Ⅰ to Class Ⅲ hydrate reservoirs, and the effect of depressurization gradually weakens.