Vol.5 No.2 2012

16/66

Research paper : Development of methane hydrate production method (J. Nagao)−90−Synthesiology - English edition Vol.5 No.2 (2012) research groups: the Research Group for Field Development Technology, the Research Group for Production Method and Modeling, the Research Group for Resource Assessment and the Administrative Coordination Section. The Research Group for Field Development Technology, coordinated by the Japan Oil, Gas and Metals National Corporation (JOGMEC), will implement offshore production tests, characterize the methane hydrate resource field, investigate offshore development systems, analyze the findings of a second onshore gas hydrate production test and implement long-term tests. The Research Group for Resource Assessment coordinated by JOGMEC will evaluate methane hydrate distribution off the coast of Japan and investigate methane hydrate systems. Within the Administrative Coordination Section, an R&D team that assesses environmental impacts has been organized to analyze environmental risks and investigate appropriate countermeasures, develop technology to measure the environmental impact, assess environmental impacts in offshore production tests and make a comprehensive assessment of the environment and optimize the assessment methods used for developing methane-hydrate-bearing layers.The MHRC at AIST coordinates the Research Group for Production Method and Modeling. The aim of this group is to establish an economical and efficient gas production method by developing technologies for advanced production methods, evaluating technologies for productivity and production behaviour and evaluating technologies for sedimentary characteristics. Research activities related to each of these R&D issues are described below.(1)Development of technologies for advanced production methodsAs mentioned above, the depressurization method can be applied to a methane-hydrate-bearing layer consisting of alternating layers of sand and mud. In such a case, the higher the initial reservoir temperature, the higher the rate of methane gas production and recovery.[12] As gas hydrate dissociation is an endothermic reaction, the gas production rate gradually decreases as the reservoir temperature decreases. Therefore, to guarantee continuous gas production by maintaining reservoir temperature at a certain range, the development of a combined production method coupling depressurization with the other production methods is being investigated. Furthermore, to ensure long-term stable methane gas production, factors that reduce permeability of the methane-hydrate-bearing reservoir should be quantitatively analyzed, e.g. impact of sand production,[13] skin formation and flow obstructions resulting from methane hydrate reproduction.(2)Development of evaluation technologies for productivity and production behaviourIn order to provide reliable predictions of productivity and production behaviours for various reservoir characteristics, the MH21-HYDRES production simulator will be upgraded. To enhance the sensitivity and accuracy of gas production behaviour, analytical models and/or routines relating to issues such as permeability of the reservoir, thermal characteristics and consolidation properties will be developed.[14] To evaluate production damage, the calculation parameters will be justified through the verification of onshore gas hydrate production tests and offshore production tests. To evaluate production behaviours in a wide area and over a long-term period, three-dimensional reservoir models that consider discontinuity, faults and heterogeneity of the reservoirs will be developed and loaded into MH21-HYDRES. On the basis of these results, a comprehensive evaluation of the production method will be performed and an optimized economical system according to the reservoir characteristics will be developed.(3)Development of evaluation technologies for sedimentary 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,

※このページを正しく表示するにはFlashPlayer9以上が必要です