1998 Fiscal Year Final Research Report Summary
Estimation of In Situ Rock Stress at a Great Depth by Means of Drilling Induced Tensile Fractures
| Project/Area Number |
08559001
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
広領域
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| Research Institution | Tohoku University |
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Principal Investigator |
HAYASHI Kazuo Tohoku University, Institute of Fluid Science, Professor, 流体科学研究所, 教授 (30111256)
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| Co-Investigator(Kenkyū-buntansha) |
OKABE Takashi Geothermal Energy Research and Develop-ment Co.Ltd., Dept.of Research & Develop-, 技術開発部, 研究員
ITO Takatoshi Tohoku University, Institute of Fluid Science, Associate Professor, 流体科学研究所, 助教授 (00184664)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Tectonic Stress / Rock Stress / In Situ stress / Geothermal Energy / Drilling Induced Tensile Fracture / DTF / DTIF / Borehole Breakout |
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| Research Abstract |
The main objective of the present project is the development a new technique estimating in situ stress in rock masses at great depths under high temperature and high confining pressure conditions, by taking advantages of drilling-induced tensile fractures (DTF). DTF is characterized by two factors, i.e. circumferential position of two macroscopic longitudinal fractures on the borehole wall and inclination of short cracks consisting of the macroscopic longitudinal fractures. Thus, at each depth range of a borehole, two sets of information are available for estimating stress state. Therefore, if there are more than three depth ranges with DTF's, it is possible in principle to set up more than six observation equations for six unknown stress components. Based on this fact, an inverse problem has been constructed, as well as the new technique for solving the inverse problem, where a statistical approach is employed to overcome the ambiguity due to the errors that are inevitably included in DTF data observed. Furthermore, a program code that is applicable for solving the inverse problem by using personal computers, has also been developed. Data of borehole breakout can also be incorporated in the new technique, if available. The validity has been confirmed by applying the technique to fictitious data sets that were constructed numerically. Finally, the new technique was applied to field DTF data obtained from three boreholes to demonstrate the applicability of the new technique to field data. The three boreholes are TG-2 of Yunomori HWR test site, HDR-2 of Hijiori HDR test site and RH-15 of British HDR test site. All these trials are satisfactory.
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Research Products
(12 results)
