1988 Fiscal Year Final Research Report Summary
Development of Tri-axial Shear-Shadow Method for Subsurface Crack Measurements.
| Project/Area Number |
62550295
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
計測・制御工学
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
NIITSUMA Hiroaki Faculty of Engineering, Tohoku University, 工学部, 教授 (90108473)
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| Co-Investigator(Kenkyū-buntansha) |
HAYASHI Kazuo Institute of High Speed Mechanics, Tohoku University, 高速力学研究所, 助教授 (30111256)
SATO Motoyuki Faculty of Engineering, Tohoku University, 工学部, 助手 (40178778)
CHUBACHI Noriyoshi Faculty of Engineering, Tohoku University, 工学部, 教授 (20006224)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Subsurface Crack / Seismic Measurement / Shear-shadow / Cross-hole Measurement / Hydraulic Fracturing / Geothermal Development / Hot Dry Rock / 地下工学 |
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| Research Abstract |
Main objective of this project is to develop a new methodology to evaluate both existence and direction of subsurface crack by cross-hole seismic measureement. Tri-axial components of transmitted shear wave through a subsurface crack, which were detected by a downhole tri-axial detector, are analyzed in the method. Main results of this project are as follows:
1. Theoretical approach: Transmitting characteristics of elastic waves at a subsurface single crack have been studied. And a methodology to evaluate a direction of the crack from tri-axial shear-shadow has been deduced theoretically.
2. Development of downhole seismic source: We remodeled an air-gun for downhole use. The remodeled air-gun generates repetitive signals in a 500 m deep borehole.
3. Development of signal analyzing system: Computer based signal analyzing system for tri-axial shear-shadow analysis has been developed.
4. Measurement of subsurface artificial crack in Higashi-Hachimantai field: Direction of an artificial subsruface crack has been evaluated by the method in Higashi-Hachimantai HDR model field. The crack, created in an intact welded tuff by a hydraulic fracturing test, is single and penny shaped. Three dimentional configuration of the crack has been deduced from the tri-axial shear-shadow analysis. The deduced direction by the analysis is almost coincide with that by tree dimentional tectonic stress measurement in the field.
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