報告書番号

U96030

タイトル（和文）

高温岩体発電のための貯留層評価技術－雄勝地点水圧破砕時の貯留層の地化学的特徴－

タイトル（英文）

RESERVOIR ESTIMATION FOR HOT DRY ROCK GEOTHERMAL POWER.-GEOCHEMICAL CHARACTERISTICS OF RESERVOIRS DURING HYDRAULIC FRACTURING TESTS AT OGACHI SITE.

概要 （図表や脚注は「報告書全文」に掲載しております）

雄勝ＨＤＲサイトで上部・下部の２層の人工貯留層を造成するために実施された水圧破砕実験時に流体の地下での挙動さらには貯留層の特徴を把握する目的で地化学調査を行った。注入水，戻り水の化学分析の結果，戻り水は地下におけるＣｌに富んだ層間水と注入水の混合および割れ目に充■された硬石膏（ＣａＳＯ４），石膏（ＣａＳＯ４・２Ｈ２Ｏ）等と注入水の反応に起因していることが明らかとなった。この観点から下部と上部の貯留層を比較した場合，下部の戻り水が混合および反応の影響をより多く受けていると判断された。これら地化学調査の結果，さらには坑井地質調査，ＡＥモニタリング等の調査結果から，上部貯留層では何種類かの方向性を有する割れ目のうち，充■鉱物の幅が大きい東西性の割れ目に沿って亀裂が伸展し，下部貯留層では，南北性の破砕帯に沿って亀裂が伸展した可能性が高い。

概要 （英文）

IN 1991 AND 1992,TWO HYDRAULIC FRACTURING EXPERIMENTS WERE CARRIED OUT TO MAKE TWO ARTIFICIAL RESERVOIRS AT DEPTHS OF 710 M(UPPER)AND 1000 M(LOWER)AT THE OGACHI HDR SITE,JAPAN. DURING THESE TESTS,A GEOCHEMICAL SURVEY WAS CONDUCTED TO EXAMINE THE FLUID BEHAVIOR IN BOTH RESERVOIRS,AND THE RESERVOIRS CHARACTERISTICS.CHEMICAL ANALYSIS OF THE INJECTED AND RETURNING WATER SHOWED THAT THE RETURNING WATER WAS DERIVED BOTH FROM MIXTURE OF THE INJECTED WATER AND THE HIGH-SALINE FORMATION WATER,AND THE INTERACTION BETWEEN THE INJECTED WATER AND ALTERED MINERALS SUCH AS ANHYDRITE(CASO4)AND GYPSUM(CASO4･2H2O)FILLING CRACKS.COMPARING BOTH RESERVOIRS,THE WATER RETURNING FROM THE LOWER RESERVOIR WAS INFLUENCED BY MIXTURE AND INTERACTION MUCH MORE THAN THAT FROM THE UPPER RESERVOIR,BECAUSE THE CHLORIDE CONTENT IN THE FORMER WATER WAS ABOUT 10 TIMES HIGHER THAN THAT IN THE LATTER AND TH CALCIUM AND SULFATE IONS IN THEWATER RETURNING FROM THE LOWER RSERVOIR INCREASED RAPIDLY COMPARD TO THAT FROM THE UPPER RESERVOR. FROM THE GEOCHEMICAL RESULTS AN THE RESULTS OF OTHER EXPERIMENT,SUCH AS AE MONITORING,FLOW MEASREMENT OF RETURNING WATER AND GELOGICAL SURVEYS,THE FRACTURE PRORESSIONS OF BOTH RESERVOIRS ARE VALUATED FLOWS: (1)IN THE UPPER RESERVOIR,THE FRCTURE EXTENDS ALONG E-W CRACKS WTH THE MOST ALTERED MINERALS OF LL CRACKS OBSERVED IN THE CORE SCTION OF THE HYDRAULIC FRACTURIN WELL. (2)IN THE LOWER RESERVOIR,THE FRCTURE EXTENDS ALONG EXISTING CRAKS CONNECTING THE FRACTURED ZONEIN A NORTH-SOUTH DIRECTION.

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