Vol.5 No.2 2012

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研究論文:Development of methane hydrate production method(長尾)−92−Synthesiology Vol.5 No.2(2012)characteristicsTo assess environmental impacts such as the stabilization of production wells, the probability of landslides and the risk of methane gas leakages from methane-hydrate-bearing sediment layers during gas production, evaluation routines called COTHMA will be developed for the sediment deformation simulator. Through a comprehensive evaluation of the mechanical properties of deep-water unconsolidated sedimentary layers by using COTHMA, the geo-mechanical stress around wells and border areas as well as long-term sediment deformation will be ascertained.3 Development of a large-scale laboratory reactor for methane hydrate production testTo commercialize gas production from a methane hydrate reservoir, the technical issues described above need to be investigated. In addition, optimal production conditions that are adaptive to prevailing methane hydrate reservoir characteristics need to be ascertained. For this purpose, production tests in reservoir fields, core analyses and predictions of gas production and geo-mechanical properties obtained using MH21-HYDRES and COTHMA will yield important results, particularly when coupled with the results of investigations of the methane hydrate reservoir structure. Field production tests will yield real productivity data on real methane hydrate reservoirs, which will enhance the accuracy of numerical simulators. However, it is difficult to conduct reproducible tests under various production conditions. Numerical simulations can provide a prediction of the productivity and the stability of a methane hydrate sedimentary layer. In addition, by introducing parameters into the numerical calculations, suitable conditions of gas production for various reservoirs can be predicted. However, these parameters are obtained from methane-hydrate-bearing core analyses, and the obtained results will be evaluated and fine-tuned through comparisons with results from the real field production tests. A dissociation experiment on methane-hydrate-bearing cores in a laboratory is useful for determining chemical and structural properties and understanding dissociation behaviour of methane hydrate distributed within pore spaces. However, because of the size of methane-hydrate-bearing cores (of the order of a few centimetres), heat transfer becomes a predominant factor. As mass transfer dominates the dissociation process in an actual reservoir field, the difference in dominant factors between core-scale experiments and field-scale production would result in a difference in gas production behaviours. As mentioned above, these R&D concepts have advantages and disadvantages and are closely related to each other, as shown in Figure 3.Fig. 3 Large-scale laboratory reactor for resolving disadvantages of production tests, core analyses and production simulations These issues are the main research concepts for establishing gas production methods and evaluating conditions in methane-hydrate-bearing layers.

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