報告書番号

N05022

タイトル（和文）

クーパーベイズンにおけるオーストラリア高温岩体地熱開発の第一期貯留層の評価

タイトル（英文）

Evaluation of the first-stage reservoir in the Australian Hot Dry Rock geothermal energy development beneath the Cooper Basin

概要 （図表や脚注は「報告書全文」に掲載しております）

オーストラリアCooper Basinにおいて実施中の深さ4,500ｍ級の坑井による高温岩体発電開発では、Geodynamics社により2003年12月に総量２万トンの水の圧入による貯留層造成が行われた。AEの解析結果によれば、貯留層は注入井から北北東および南南西へそれぞれ約1,600ｍ広がり、深さは4,100～4,600ｍの範囲にあること、振幅が大きなAEはその後の亀裂の進展方向と関係があることなどが推定された。また、既往文献や注入井の掘削ズリの解析結果によれば、高温岩体と見なされている花崗閃緑岩は、熱的に安定しており、非常に大きな広がりであることから熱的ポテンシャルは膨大であると評価される。さらに、電磁探査の結果、深さ5,000ｍ程度までの比抵抗構造が推定された。これにより、将来比較的高比抵抗の地表水が大量に地下に圧入されると、その分布が比抵抗探査により評価できる可能性がある。

概要 （英文）

A new Hot Dry Rock (HDR) geothermal power generation project has been conducted at Cooper Basin, South Australia by Geodynamics limited (GDY) since 2002 after the renewable energy electricity ACT2000 enacted. In this project, a water injection well, Habanero #1, was drilled to a depth of 4,421 m. The bottom-well temperature was estimated more than 250 degree C. A first-stage HDR reservoir was created by hydraulic stimulation with a total of 20,000 tons of water in 2003. The reservoir was evaluated to have enough volume for expected heat extraction in the first-stage. A production well, Habanero #2, was drilled to intersect the reservoir based on the AE hypocenter locations in 2004. The Central Research Institute of the Electric Power Industry (CRIEPI) has joined the Cooper Basin project under the collaboration agreement with GDY and Commonwealth Scientific and Industrial Research Organization (CSIRO). In this collaboration CRIEPI has applied the methods which were developed in the HDR projects at Ogachi and Hijiori in Japan to evaluate the geological structure and the reservoir artificially created at Cooper Basin. CRIEPI has conducted the geological analysis of cuttings from Habanero #1, the electromagnetic method for investigating the resistivity structure in the site and the AE measurement for the created reservoir evaluation. From the geological analysis it was inferred that the basement rock (granodiorite) at the site has large volume and has been kept high temperature for long time, about 80 million years. This means huge thermal potential in the site. Feldspar veins rich in albite are thought to be key fractures for reservoir propagation. From the electromagnetic survey results of the CSAMT and TDEM methods the underground resistivity structure was estimated. The structure shows to have very low resistivity continued to deep underground of 5,000 m. The resistivity structure will be used as an original condition for evaluating injected water distribution in the future. From the AE measurement results the reservoir was evaluated to have lengths of 3,200 m in northeast-southwest direction and 1,800 m in northwest-southeast direction from 4,100 m to 4,600 m in depth. This extension size is thought to be enough for the expected fist-stage scale.Referring the results obtained by CRIEPI, GDY has drilled a production well, Habanero #2 and been conducting water communication tests between Habanero #1 and #2 through the reservoir. After completion of constructing a water circulation system, GDY plans to conduct continuous steam production for two or three months near future.

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