石油技術協会誌

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Methane Hydrate （MH） is well known as one of the unconventional resources, which is confirmed to exist abundantly offshore in Japan. A variety of studies have suggested that the depressurization is the most effective method for developing MH from the commercial and technical points of view. In the development of MH by the depressurization method, the dissociation and production of MH must greatly influence the geo-mechanical behaviors such as compaction/deformation of formations and vice versa. Hence, to rigorously predict the MH reservoir performances, it is essential to take account of the flow and geo-mechanical behaviors simultaneously.

First, we developed a program for coupling the MH flow simulator （MH21-HYDRES） and the geo-mechanics simulator （COTHMAs）, which were developed under The Research Consortium for MH Resources in Japan （MH21 Research Consortium）, enabling simple explicit coupling （ECM） and iterative coupling （ICM）. As a result of the simulations using this program, it was confirmed that ICM could precisely predict MH reservoir performances in conjunction with geo-mechanical behavior, but the computation became far slower than uncoupled simulations by MH21-HYDRES.

Second, we incorporated two functions into the program to improve the practicality, that is hybrid coupling （HCM） and dual-grid system （DGS）. In the simulations using the HCM, the ICM is applied only to the grid blocks （or elements） with noticeable strain/deformation, while the ECM is applied to those with negligible strain. In the DGS, the sizes of flow simulation grid blocks and geo-mechanics simulation elements can be defined independently. The simulation studies using the program revealed that the HCM could remarkably shorten the computational time without compromising calculation accuracy. It was also confirmed that the combination of the HCM and the DGS could dramatically reduce the computational time, although the calculation results were slightly different from those with smaller elements

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