Vol.7 No.4 2015

Research paper : Applicability of the technologies to the assessment of methane hydrate sediments (N. TENMA)−227−Synthesiology - English edition Vol.7 No.4 (2015) AuthorNorio TENMAJoined the Agency of Industrial Science and Technology’s National Institute for Resources and Environment in 1990. Specialized in numerical modeling and evaluation of heat extraction characteristics of geothermal reservoirs, and engaged in the development of numerical simulators. Transferred to AIST’s Methane Hydrate Research Center in FY 2009 to engage in the development of a geo-mechanical simulator for MH development. Currently aims to develop the evaluation technologies for sedimentary characteristics.Discussions with Reviewers1 Overall commentComment (Hiroshi Tateishi, AIST Chubu; Yusaku Yano, AIST)This paper gives an overview of the developmental technology system for the “evaluation technology of sedimentary characteristics” within the R&D process at AIST’s Methane Hydrate Research Center. The paper aptly summarizes the role of the Center in MH21, which is the administrative center of the national project for MH resource exploration, and the development of a geo-mechanical simulator which is the core technology, and evaluation of well integrity and wide-area deformation based on simulations. We consider this paper appropriate for Synthesiology.2 The global positioning of MH developmentQuestion (Yusaku Yano)This paper discusses the technological development of MH exploration in Japan, which I believe is a challenge not faced anywhere else in the world in terms of new technology development. The readers may wish to know about the positioning of this technological development on the global stage. As background, in which regions or countries are MH resources distributed, and what is the level of technological development in other countries? What is the positioning of the Japanese technology concerning MH? Also, although MH21 has written a roadmap for development in Japan, are there any international research collaborations with the rest of the world? Is there a global roadmap?Answer (Norio Tenma)For the exploration of MH as a new resource, surveys are being carried out in the United States, Russia, Canada, China, and India, but their aims are chiefly to study the volumes of resource. Actual production technology is not being researched elsewhere in the world. Therefore, as concerns to global positioning, I have added the paragraph: “Similar research is in progress around the world, such as in the United States, Korea, China, and India. For example, Korea is engaging in a gas hydrate survey in the Tsushima Basin, and the US is surveying reserves, along with the earthquake exploration surveys, in the Gulf of Mexico, however, no offshore production tests have yet been conducted.”3 Relationship to existing resource exploration researchQuestion (Yusaku Yano)On the point of using wells for production, MH is similar to conventional oil and natural gas, but I think you are adding a unique MH technological system to existing advanced technological systems for oil and natural gas production. Unlike the construction of a technological system from blank, when adding a new technological system onto a large existing technological system, I believe one thinks of doing it more efficiently and effectively. For the development of evaluation technologies for sedimentary characteristics, is there previous research on oil and natural gas that could be referenced, and is the research progressing effectively by improving on such earlier research? Are you actually engaging in such activity?Answer (Norio Tenma) We believe that sediment deformation, such as subsidence while applying the depressurization method, is an important challenge when investigating the potential for long-term, stable production. The topic of subsidence, for example, has been investigated in the field of water-soluble natural gas exploration. We assume that a similar phenomenon will occur in MH exploration. We engaged in R&D to gain an understanding of the mechanical characteristic of the MH bearing sediment and to evaluate using numerical simulation, using approaches similar to those employed for natural gas extraction. For example, when understanding the mechanical characteristics of MH, we assumed that MH had been newly added to the sediment layer, so the research was done in reference to the test methods used in soil mechanics. Specifically, since our MH samples are affected by pressure and temperature, we investigated a method of conducting mechanical tests while controlling these factors. As described in subchapter 3.1, “Development of the geo-mechanical simulator,” the MH simulated sample was made by injecting gas into the frozen sand sample. There was no method for calculating the specific physical property values until this method had been established, so we regard it as a major accomplishment. However, we have conditions that are not encountered in conventional research, such as the target of exploration being a non-consolidated layer several hundred meters below the seabed floor, not to mention the near-explosive depressurization that takes place when using the depressurization method (about 7 MPa depressurization in the first offshore production test). We are now conducting our research taking these differences into full account.4 Relationship with the offshore production testQuestion (Hiroshi Tateishi)In the offshore production test in March 2013, what preliminary contribution did this research make? Or was the simulator unable to make specific predictions since it was incomplete? As about one year has elapsed since the test, can you make any remarks about the results or their interpretation? I do understand that you may not be able to talk about the results for reasons of confidentiality, but considering the fact that you are two years into Phase 2 according to the schedule, I get the impression from this paper that it started with a bang but ended in a whimper.Answer (Norio Tenma)The analysis results were used as basic data for designing the wells for the first offshore production test and for setting the monitoring wells. However, a range of verifications are being carried out using the data from the first offshore production test, and as mentioned in this paper, we are still in the process of data verification for constructing and analyzing the numerical model and laboratory experiments. Therefore, the paper is simply a report on the current status.5 Significance of development of the simulatorComment (Hiroshi Tateishi)While I understand that the development of a simulator is a key pillar of this research, the role and significance of the


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