Vol.7 No.4 2015
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Research paper : Applicability of the technologies to the assessment of methane hydrate sediments (N. TENMA)−220−Synthesiology - English edition Vol.7 No.4 (2015) method was proposed for reasons of its energy efficiency. In Phase 2, the depressurization method is being applied to further develop the complex production method (combined method) to stably produce large volumes of methane gas, to improve the production simulator (MH21-HYDRES) by looking at how closely its predictions match the actual production tests, and to evaluate wide-area sediment deformation that takes place during methane gas production. Specifically, methods of obtaining a high productivity and recovery rate are being developed as “technologies for advanced production methods,” and long-term, stable production is attempted through the development of quantitative analysis and numerical models of the production impediment factors such as sand problems, skin formation, fine-grain sand accumulation, decreased permeability due to compression, or flow blockages that occur during MH reformation, as well as the development of technologies to control and counter such impediments. We also engage in research into “evaluation technologies for productivity and production behavior” with the aim of developing a practical simulator by increasing the accuracy of the production simulator, through the development of a reservoir model to which the discontinuity and heterogeneity of the reservoir are introduced as parameters, and its degree of matching with laboratory experiments. Research on “evaluation technologies for sedimentary characteristics” is also being done to guarantee the long-term safety of the sediment deformation and consolidation behavior due to methane gas production from the MH layer.3 Evaluation technologies for sedimentary characteristicSince sediment deformation accompanying gas production from the MH layer is predicted, the development of technology that ensures safe and secure production in the development areas over the long-term is important for reasons of social and legal acceptability. This is particularly true for the development areas as shown in Fig. 3, in which it is necessary to evaluate the effects of fault discontinuity and sediment heterogeneity on seabed floor subsidence or sediment deformation, along with deformation behavior within the MH layer. It is also necessary to analyze the changes in deformation and strength of the sediment from the early stage of development to be able to evaluate the long-term effects through comparison of factors before development to after well abandonment. Moreover, since there will be large stress differences in the well during the application of the depressurization method, it is necessary to analyze the stress on the well and to evaluate well integrity throughout the production period. To solve these issues through “sedimentary characteristic evaluation technology,” the Research Group for Production Method and Modeling is engaged in: (1) development of a geo-mechanical simulator, (2) evaluation of well integrity, and (3) evaluation of wide-area deformation, on which the R&D is being carried out in collaboration with private companies and universities within the MH21 framework.Specifically, for (1) the development of the geo-mechanical simulator, the COTHMA, which will be explained later, is being developed. Various mechanical parameters of the MH layer are also being collected to enable the assessment of the deformation and compression behavior of the MH in the simulator.In (2), the evaluation of well integrity, the sediment deformation and stress distribution in the vicinity of the production well during the application of the depressurization method are analyzed and evaluated based on the geo-mechanical simulator. Physical properties of wells for well integrity estimation are also being collected.Moreover, in (3) evaluation of wide-area deformation, the method of analyzing the effects of discontinuities such as faults and sediment heterogeneity on seabed floor subsidence or sediment deformation are being surveyed and investigated; and sensitivity analysis using the simulator is being carried out. The sediment deformation and change in strength during the period from start of development to well abandonment are analyzed, and the long-term effect of development is evaluated by comparison with the situation before MH development. These subjects are interrelated as shown in Fig. 4. The goal is to develop a “geo-mechanical simulator” that combines the knowledge of “evaluation of well integrity” with “evaluation of wide-area deformation” (which will be explained below), and ultimately to provide various information necessary to plan the MH development.With the framework of MH21, the Reservoir Simulator Team of MHRC collects mechanical parameters through laboratory experiments for (1) the development and advancement of the geo-mechanical simulator, and applies integrated evaluation of the mechanical characteristics of the deep-water unconsolidated deposit layer that is unique to MH Fig. 3 Development of evaluation technologies for sedimentary characteristics in the MH developmentTo establish a long-term, safe, and secure production method, it is necessary to solve various issues on sedimentary characteristics.Migration of CH4 and waterGeological characteristicHydrate dissociationReservoir deformationMH reservoirFault characteristicSeabed surface subsidenceWell integrityMH developmentResearch element

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