報告書番号

U99018

タイトル（和文）

高温岩体発電のための貯留層評価技術 --トレ－サテストによる雄勝貯留層の体積評価--

タイトル（英文）

Technology of Reservoir Estimation for Hot Dry Rock Geothermal Power- Volumetric Estimation of the Ogachi Reservoir by Tracer Test -

概要 （図表や脚注は「報告書全文」に掲載しております）

雄勝貯留層の特性を評価する目的で雄勝HDRサイトにおいて抽熱循環時にトレ－サテストを実施した。得られた応答カ－ブから、2流路モデルによる数値解析により、上下部貯留層に対応する応答カ－ブを求め、これらのカ－ブから貯留層体積などの特性を評価した。(1)数値解析のカ－ブフィッティングから、雄勝貯留層は単純な2流路というよりは複数の流路が存在する可能性が高い。(2)貯留層の最も優勢な流路の体積を表すモ－ド体積は、上部で6～12m3、下部で117～289m3であり、下部が上部に比べ極めて大きな値を示す。下部の体積は徐々に小さくなる傾向があり、特に1995年に急激に小さくなっている。(3)分散の定性的な評価の指標となる1/2モ－ド値幅は1994～1995年にかけては徐々に減少し、分散が小さくなるのに対し、1997年は逆に増加することから、サンドプラグのフラクチャへの挟在、沈殿鉱物の生成等に起因する可能性が考えられる。

概要 （英文）

In order to characterize the Ogachi reservoir, four tracer tests have been carried out successfully, twice in 1994, once in 1995 and 1997, respectively, at the CRIEPI's Ogachi HDR site in Akita prefecture, Japan. Since the response curve obtained from the tracer monitoring involves two curves due to the two reservoir, the upper reservoir and the lower reservoir, a numerical simulation of two flow path model was done to separate the response curve each other. Using the response curves obtained by monitoring and calculation, the characteristics of the Ogachi reservoir was estimated. The results are as follows;1) Considering the fitting of the synthesized and observed curves, the Ogachi reservoir is evaluated to have multiple path system.2) Modal volumes of the upper reservoir are estimated 8.4m3 in 1994's 1st test, 11.7m3 in 1994's 2nd test, 6.6m3 in 1995, and those of the lower are estimated 289m3, 236m3,117m3, respectively. Through the circulation tests, the modal volume of the lower reservoir decreases gradually, and in 1995 test, the modal volume decreases remarkably, because of permeability improvement of the lower reservoir performed before the circulation.3) Values of width at 1/2 height which is assumed to represent dispersion of the reservoir decreases between 1994 and 1995, but the value increases in 1997. This increase is supposed to be based on the pluging to the fracture of the sand which is used before circulation, or the precipitation in the fracture because of the cooling down in the reservoir due to huge water injection to the reservoir before circulation.

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