Transportation Method of Methane Hydrate Collected in the Recovery Area of Sea of Japan based on Energy Payback Ratio (EPR)

Background In recent years, much focus is being placed on methane hydrate as a new energy resource. Bearing of methane hydrate in the surrounding sea areas of Japan has been confirmed, and surface type methane hydrate is frequently discovered in the Sea of Japan side. These methane hydrates exist on the surface of seafloor and, also in shallow areas, approximately within 100m under seafloor in clumps and veins. Starting in FY2016, the Japanese government chose 6 institutions for their 3-year project for each institution to investigate a method to recover surface type methane hydrate. Tokyo University of Marine Science and Technology, 1 of the 6 institutions, exercised EPR and economic evaluations on a method to transport methane hydrate from offshore platform to the vessel, and another method using seafloor pipelines. Development of the recovery techniques of surface type methane hydrate will finally begin in FY2020.

Purpose The purpose of this study is to determine the most suitable transport method of methane hydrate with high EPR, collected in the Sea of Japan, in order to use it as an energy resource. Transport method based on EPR will be necessary in order to consider a method to transport methane hydrate from Umitaka Spur.

Method Energy Payback Ratio (EPR) is calculated by dividing the total energy produced by the amount of energy used. The amount of energy used can be grouped into facility energy and operation energy. Facility energy includes material energy, production energy, transport energy, and construction energy, whereas operation energy consists of mining energy and repair maintenance energy. Recovery method, number of methane hydrate sites, distance from methane hydrate recovery area to the nearest coast are used as parameters to assess energy payback ratio. As for the recovery method, the recovery speed of methane hydrate is relatively fast, therefore, a method which one site can recover methane hydrate in 10 years was selected. Recovery speed of tractor method is 270 m3/day and the recovery speed of shaft wall mining method is 314 m3/day. If 5 or 6 machines are operated simultaneously, the recovery will be completed in approximately 10 years. The number of methane hydrate sites will be 5 different cases with 1 to 5 points per case. The distance from the closest coast to the site is an important factor to specify the length of the pipeline and it will affect the construction cost and facility energy significantly. In this study, the author will discuss 10 cases in the range of 10km～100km. Methane hydrate will be transported to the offshore platform and transported on either a vessel or through a pipeline. Transportation methods will be ① compressed natural gas (CNG) carrier, ② pipeline via Iwafune offshore oil-gas field, ③ pipeline to Higashi Niigata thermal power station, ④ pipeline via submarine canyon in the east side of Itoigawa.  Result By examining the four transport methods, the author was able to conclude the transport method with the highest EPR. The result of the most suitable transport method to use methane hydrate recovered in the Sea of Japan as an energy resource will be announced in the presentation at AGU.