| Summary: | 碩士 === 國立成功大學 === 資源工程學系 === 107 === Gas hydrates are solid ice-like component composed of water molecules and small size gas molecules, which exist in the condition of high pressure and low temperature. Due to the stable condition of hydrate, it is an unconventional gas resources that widely spread over deep oceanic sediments and permafrost regions. According to the exploration, there are also gas hydrate resources in southwestern Taiwan. There are 3 classes of gas hydrate deposits. Because of the existent of free gas zone beneath the hydrate layer, the class 1 gas hydrate is considered to be the most profitable production target. Most of the marine hydrate resources are found in unconsolidated sedimentary formation. Therefore, there is a risk of potential geohazard caused by seafloor subsidence and hydrate dissociation during the hydrate deposit production. Targeting at the marine class 1 hydrate deposits, the purpose of this study is to establish a safety operation strategy to produce the gas resource from the free gas zone. The CO2 EGR strategy is applied to stabilize the reservoir pressure preventing seafloor subsidence during the gas production. CMG STARS simulator is used to calculate the reservoir production and the geomechanics behavior of the formation. In this study, different operation strategies are tested and discussed to figure out the relevance between the operation methods and the production performances. The results suggest that the CO2¬ breakthrough control is essential to the application of CO2 EGR strategy. Later CO2¬ breakthrough results in greater gas production. By applying CO2 injection delay or lower injection pressure, the production can be extended and result in higher production with more severe situation of formation subsidence and hydrate dissociation. Allowing more CO2 content in produced gas can benefit the overall production without subsidence.
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