報告書番号

U86032

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－水圧破砕で発生するＡＥの特性と破壊メカニズム－

タイトル（英文）

SOURCE LOCATION AND FOCAL MECHANISM OF AE EVENTS DURING THE HYDRAULIC FRACTURING

概要 （図表や脚注は「報告書全文」に掲載しております）

水圧破砕法は岩盤応力測定や石油井および地熱井の刺激法として利用される他，最近では高温岩体発電システムの中核をなす人工貯留層の造成法としても注目されているが，水圧破砕によるき裂の発生と進展のメカニズムについては不明の点が多い。このため，水圧破砕による岩盤破壊メカニズムの解明と造成された人工貯留層の進展や広がりを評価する技術の開発を目的として，野外で小規模な実験を行い，主としてＡＥを用いて水圧破砕によるき裂の進展過程を調べた。その結果，ＡＥの震源分布や発電機構などの解析から，今回の実験で発生したき裂は引張り破壊によるものではなくせん断型であることが判明した。また，ＡＥの震源分布は既存の節理方向と良い一致を示すことから，水圧破砕による岩盤のき裂の進展や広がりを予測するうえで，節理分布の把握が重要であると考えられる。

概要 （英文）

A SMALL SCALE HYDRAULIC FRACTURING EXPERIMENT WAS CARRIED OUT TO CHARACTERIZE THE AE ACTIVITY ASSOCIATED WITH THE HYDRAULIC FRACTURE PROCESS. IN TOTAL,34 AE SENSORS WERE INSTALLED IN THEBORE HOLETO SURROUND THE HYDRAULIC FRACTURE ZONE AND DETERMINE LOCALIONS OF AE HYDOCENTERS PRECISELY. THE RESULIS OF THE EXPERIMENT ARE SUMMRIZED AS FOLLOWS. (1)AE ACTIVITY SEEMS TO DEPEND ON THE INCREASE OF THE FLOW RATE. IF FLOW RATE WAS INCREASED THEN AE ACTIVITY WAS ALSO INCREASED. AE ACTIVITY OCCARRED REMARK ABLELY WHEN THE FLUID PRESSURE REACHED THE BREAK DOWN PRESSURE. (2)THE TIME HISTORY OF THE EVENTS WAS THAT THEY STARTED AT THE BOREHOLE AND MIGRATED AWAY FROM THE BOREHOLE. DISTRIBUTION OF THE HYPOCENTER LOCATIONS OF 4 AE EVENTS AT THE VARIOUS DEPTHS MADE THE PLANES AT THE SAME DIRECTION AND DIP ANGLE. THE ORIENTATION OF FRACTURES DETERMINED FROM AE MAPPING WERE CONSISTENT WITH THOSE OF THE PRE-EXISTING NATURAL JOINTS REVOALED BY THE OBSERVATION WITH A BOREHOLELELEVISION. (3)THE RADIATION PATTERNS INDICATED THAT MOST OF AE EVENTSOCCURRED WITH SHEAR FRACTURE. DIRECTION OF TENSION AND COMPRESSIONAXISDETERMINED BY THE FOCAL MECHANISM SOLUTIONS WERE CLOSE TO THOSE OF PRINCIPLE STRESS OBTAINED BY THE HYDRAULIC FRACTURING TECHNIQUE. THEREFOR,THE HYDROFRACTURED PLANES IN THIS EXPERIMENT WERE CREATED WITH SHEAR FRACTURE AND PROPAGATED ALONG PRE-EXISTING NATURAL JOINTS. (4)THIS STUDY DEMONSTRATES THAT AE MONITORING CAN BE USED TO DEFINE THE GEOMETORY OF THE HYDRAFRACTURE AND PROVIDE USEFULL IMFORMATION ON THE MECHANISM OF HYDRAULIC FRACTURING.

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