| Summary: | 碩士 === 國立成功大學 === 資源工程學系碩博士班 === 91 === The purpose of this study is to investigate the dissociation mechanism in connection with its physical and/or chemical properties and then to estimate the gas production using thermal recovery and depressurization recovery. A simple energy balance method is used to calculate the recovery of gas hydrates. In additions, hot steam injection method, Huff and Puff method and depressurization method are also used to calculate the decomposition of gas hydrates, radius change with time and the quantity of natural gas released from gas hydrate.
In the study of simple energy balance method, the net gas recovery efficiency is probably below 10% in which the heat injection efficiency and the combustion efficiency are both 50% (the cost and recovery time do not take into consideration).
The modified model (Marx and Langenheim, 1959) had been used in this study to calculate the dissociation area and the cumulative methane gas production changing with time. It is assumed that the thickness of reservoir is 30m, the reservoir porosity is 30%, the saturation of gas hydrates is 20%, and the hot steam injected into the reservoir with constant rate (the hot steam injection rates are between 208B/D and 1040B/D). When the hot steam injected into the reservoir about 16 years, the dissociated radius of hydrates are between 23m and 51m, and released natural gas about 2.5*106 SCM to 1.3*107 SCM.
In using the Huff and Puff recovery technique with hot steam injection for 16 years, the dissociated radius of hydrates is about 45m and released natural gas about 2.5*106 SCM. The heat loss in the hot steam injection and in the reservoir is a large portion.
In the depressurization method, hydrates dissociate by means of decrease the reservoir pressure, and the effect on the gas production by several pressure drops is studied. By the assuming reservoir parameters and the reservoir permeability of 1mD, the radius of dissociated hydrates are between 41 m and 93.7m, for the case of producing the gas for 16 years at constant production rate (the rates are between 300SCMD and 1500SCMD). The pressures of the reservoir are between 42 atm and 49 atm.
Based on the results of this study, there is no feasibility to recovery gas hydrate by using thermal recovery and depressurization recovery under current technology. More economic and efficiency recovery methods should be studied.
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