Vol.5 No.2 2012

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研究論文:Development of methane hydrate production method(長尾)−91−Synthesiology Vol.5 No.2(2012)eastern Nankai Trough. For the first time, the validity of the depressurization method was verified by means of an onshore gas hydrate production field test conducted in March 2008 in a permafrost zone in Canada. In phase 2, from FY 2009 to 2015, the use of methane hydrate extracted off the shores of Japan will be evaluated as a highly reliable energy resource. In addition, although it has been known that the depressurization is a useful method for gas production from methane hydrate reservoirs by laboratory characterization of core samples, the technical difficulties of commercializing gas production from methane hydrate reservoirs will be studied, where the commercialization will be inducted by public and private sectors in phase 3 from FY 2016. The MH21 Research Consortium has set up four 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

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