Tight Oil Potential in Japan

Abstract

The Onnagawa Shale is bio-siliceous, Monterey-like and the main source rock in Japan, particularly in Akita basin, with fairly high potential. It is 500m thick in average and has TOC of 2 % in average, up to 5 % in part, and HI of 500 mg/gC typically. The Onnagawa is under review in the light of Shale oil/gas, comparing the Monterey shale. As the first step, we have reviewed the Yuihara-Ayukawa field, where the largest commercial oil & gas production from the Onnagawa Shale is ongoing. In the field, various reservoirs, including Dolerite, Tuff and quartzose porcelanite probably fractured, seem to have a common gas-oil contact. In other words, they constitute one pressure system. The maturity of the hydrocarbon in this system is much higher than that of source rocks close to the reservoirs, which indicates normal migration process. We also have sub-commercial production or intense oil show from relatively tight reservoirs that is typically alternation of porcelanite and tuff. The maturity of the oil, however, is lower than that of commercial oils and close to that of early-matured source rocks around. In summary, we have two different hydrocarbon accumulations in one field. One is productive, mature and probably migrated, and another is sub-commercial or non-productive so far, less matured and indigenous. In addition, we have other similar examples in the Akita basin and we think this less-matured oil group as a part of basin-wide shale oil system, where our field is located in the transition zone just above oil generation window. We expect a potential with an order of 100 million bbl in this basin including the kitchen. Now the first pilot test is being planned to apply horizontal drilling and massive stimulation treatment to "shale oil or tight oil" in this basin.