報告書番号

U91008

タイトル（和文）

高温岩体発電のための岩盤破砕・評価技術の開発－水圧破砕に伴うＡＥと破壊メカニズムに及ぼす岩石の粒径と破砕流体の粘性効果

タイトル（英文）

DEVELOPMENT OF FRACTURE EVATUATION TECHNIQUEFOR HDR GEOTHERMAL ENERGY EXTRACTION-CHARACTERISTICS OF AE INDUCED BY HYDRAULIC FACTURING

概要 （図表や脚注は「報告書全文」に掲載しております）

水圧破砕法は高温岩体発電の人工貯留層の造成法として利用される。しかし，水圧破砕の破壊機構はまだ不明な部分もあるため，岩種や破砕流体の粘性をパラメータとした実験を行い，これらが水圧破砕の破壊機構に及ぼす影響について検討した。その結果，（１）細粒の大理石や斑晶質の安山岩では，ＡＥは岩石が割れる瞬間のみ発生するのに対し，粗粒の花崗岩では岩石が破壊する少し前からＡＥが発生し始め，破壊後も活発に発生する。（２）粘性が水より大きい油を岩石試料に圧入すると，大理石や安山岩の試料でも岩石が割れる前からＡＥが発生し始める。また，水を注入した場合，ほとんどのＡＥはせん断破壊により発生するのに対し，油を圧入した場合では，亀裂の先端で発生するＡＥは引張り破壊で発生する。このように，岩石中の結晶の大きさや圧入する流体の粘性の程度により，水圧破砕に伴うＡＥの発生状況や割れ目の出き方に大きな相違の出来ることが判った

概要 （英文）

SOME LABORATORY HYDRAULIC FRACTURING EXPERIMENTS WERE CARRIED OUT ON 20-CM SQUARE BLOCKS OF FINE-GRAINED MARBLE,COARSE-GRAINED GRANITE AND ANDESITE TO CLARIFY THE EFFECTS OF THE ROCK GRAIN SIZE AND THE VISCOSITY OF THE INJECTED FLUID ON THE FRACTURE MECHANISM. EIGHT TRANSDUCERS WERE USED TO DETECT ACOUSTIC EMISSION (AE) EVENTSASSOCIATED WITH THE FAILURE,AND TO RELATE THE AE ACTIVITY TO THE HYDRAULIC FRACTURING PROPERTIES. THE RESULTS ARE AS FOLLOWS: (1) ROCK SAMPLES WERE HYDROFRACTURED USING WATER. THERE WAS LITTLE AE ACTIVITY IN FINE-GRAINED MARBLE OR ANDESITE AND AE OCCURRED WHEN FRACTURING OCCURRED. ON THE OTHER HAND,THERE WAS A LOT OF AE ACTIVITY IN THE COARSE-GRAINED GRANITE AND AE OCCURRED AT ABOUT 90% OF THE FRACTURE PRESSURE. (2) THEREWAS MORE AE ACTIVITY IN THE MARBLE,ANDESITE AND GRANITE AND IT OCCURRED BEFORE THE FRACTURING WHEN OIL WAS USED AS THE FRACTURING FLUID. (3) ALL AE EVENTS IN THE THREE TYPES OF ROCKS WERE CAUSED BY SHEAR FAILURE WHEN THE FRACTURING FLUID WAS WATER. FROM THE RADIATION PATTERN OF THE FIRST P-WAVE MOTION THERE WAS NO EVIDENCE OF TENSILE FAILURE IN THESE SAMPLES. ON THE OTHER HAND,AE EVENTS WERE PRIMARILY DUE TO TENSILE FAILURE INFERRED FROM THE FOCAL MECHANISM WHEN OIL WAS USED AS THE FRACTURING FLUID. (4) THIS RESULT SUGGESTS THAT THE HYDRAULIC FRACTURING MECHANISM IS STRONGLY INFLUENCED BY THE ROCK GRAIN-SIZE,THE VISCOSITY OF THE INJECTED FLUID,AND THE STRESS CONDITION OF THE ROCK. (5) THE FRACTURE PLANE ESTIMATED FROM AE HYPOCENTER DISTRIBUTIONS AGREED WELL WITH THAT OBSERVED FROM THE SURFACE OF ROCK SPECIMENS AND CORES. THEREFORE,AE IS VERY USEFUL FOR MONITORING THE EXTENSION OF HYDRAULIC FRACTURING.

報告者

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