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Short-term Flow Tests of Exploratory well for Geothermal Energy Development conducted in the Oyasu region of Akita Prefecture

Since 2011, Idemitsu Kosan Co.,Ltd. (Head Office: Chiyoda-ku, Tokyo; Representative Director and CEO: Takashi Tsukioka), INPEX Corporation (Head Office: Minato-ku, Tokyo; Representative Director, President & CEO: Toshiaki Kitamura), and Mitsui Oil Exploration Co., Ltd. (Head Office: Minato-ku, Tokyo; President and CEO: Mitsuo Hidaka) have, with the assistance of the Japan Oil, Gas and Metals National Corporation(JOGMEC), been carrying out joint exploration of geothermal energy development in the Oyasu region of Akita Prefecture, Japan. Recently, short-term flow tests of geothermal exploratory well were conducted to measure the capacity of well.

1. Conditions affecting geothermal energy development

Japan is home to approximately 10% of the world’s geothermal energy resources, giving it the third largest geothermal potential in the world after the United States and Indonesia.
Geothermal power generation is attracting attention as a renewable energy source capable of delivering stable supplies of electricity unaffected by weather conditions. Thanks to deregulation of geothermal energy development in national and quasi-national parks since the Great East Japan Earthquake and the enactment of feed-in tariff system for renewable energy, today geothermal exploration and development are underway across Japan. The three companies noted above, each of which possesses geothermal expertise in areas such as exploration of underground resources, drilling wells, and steam supply, have been engaged in joint development efforts in the Oyasu region since 2011.

2. Overview of these exploration efforts through now

(1) Stage 1: Completed in FY2011

Surface surveys (ground-surface geological survey, gravitational exploration, electromagnetic exploration, etc.)

(2) Stage 2: FY2012-2017 (planned)

(i) Drilling survey, building of roads for bringing in equipment, etc.
Exploration wells* OYE-1-7 are being drilled to investigate matters such as the geological structure, underground temperatures, and water permeability.
* Drilled exploration well: A well drilled in the initial stages of exploration to investigate matters such as the underground structure and retention of geothermal heat

(ii) Hot-spring monitoring survey
Hot-spring temperatures, yields, and chemical composition are being monitored in nearby hot-spring wells.

3. Details and objectives of these efforts

Among the drilled exploration wells since FY2012, short-term flow tests of exploratory well*were conducted at Well OYE-6, drilled in FY2016. Through these experiments, we are carrying out detailed verification of well production capacity (volume of steam), underground temperature, chemical composition of geothermal fluid, water permeability in the vicinity of the well, and other matters.

* Short-term flow tests of exploratory well: Short-term experiments used to check for steam, conducted together with drilling well.

4. Future schedule

We have decided to advance to Stage 3 studies (including drilling of additional exploratory wells*, production and injection experiments, evaluation of reservoir capacity, and environmental assessment) based on the results of these short-term flow tests of exploratory well and future study during FY2017.

* Additional exploratory wells: A well of the same size as a production or injection well, used to test production and injection over several weeks
Outline of these short-term flow tests of exploratory well
Outline of these short-term flow tests of exploratory well
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