2007 Fiscal Year Final Research Report Summary
Specification of borehole mode contributes to frequency domain acoustic logs
| Project/Area Number |
18560778
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Earth system and resources enginnering
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| Research Institution | Hirosaki University |
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Principal Investigator |
SAITO Hiroyuki Hirosaki University, Hirosaki University, Graduate School of Science and Technology, Associate Professor (70264091)
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| Project Period (FY) |
2006 – 2007
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| Keywords | Acoustic logging / Borehole mode / Stoneley mode / Subsurface fracture / Permeability |
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| Research Abstract |
The ability of the frequency-domain Stoneley wave log to detect formation boundaries have been tested with field data. The dominant frequencies of Stoneley waves are highly dependent on formation properties. Formation boundaries detected from the frequency-domain Stoneley wave logs are in excellent agreement with the logs of degree of welding and lithology in the well EE-4 of the Higashi-Hachimantai geothermal field.
And, a new technique to detect thin permeable fractures in a well in which the elastic properties of the surrounding rock vary widely has been proposed. The method utilizes several Stoneley wave amplitude logs at different frequencies. The location of a permeable fracture detected with this technique agrees with the result of acoustic logging with full well-bore pressurization.
In addition, overshoot and its oscillation appearing on the transmission coefficient of Stoneley wave have been investigated. The overshoot and its oscillation are attributable to backflow of borehole
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fluid from the permeable fracture zone. The characteristic of oscillation in the backflow wave is similar to the refection wave, though the magnitude of the backflow wave is larger than that of refection wave. Therefore, the period of oscillation appearing on transmission coefficient is concerned with the thickness of a permeable fracture zone. The detailed modelling of backflow wave is important for developing a new characterization method of the permeable fracture zone.
These examples demonstrate that the frequency-domain Stoneley wave log can be used as an effective method for detection of formation boundaries and permeable fractures. The proposed technique does not require knowledge of the wave source spectrum. Only multiple Stoneley amplitude logs at different frequencies are required. The proposed technique is therefore applicable not only to logging data obtained with a broad-band logging tool, but also to the use of a variable-frequency logging tool, although in the latter case repeated measurements at different frequencies are required. Less
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Research Products
(8 results)
