CROSS-HOLE SEISMIC SURVEYS: APPLICATIONS FOR STUDYING SUBSURFACE FRACTURE SYSTEMS AT A HOT DRY ROCK GEOTHEMAL SITE

The use of cross hole seismic surveys for delineating the location and size of subsurface fracture systems is investigated. The radiation pattern for P and S waves emitted by a seismic source in a borehole is derived. Experimental work in relatively homogeneous granite suggests that the derived relationship adequately describes the radiation patten for both explosive sources and acoustic transducers placed in fluid-filled boreholes. Using the above functional expressions for the S- and P-wave amplitudes, we have developed a technique to estimate Q and locate discrete fractures in crystalline rock that compose the Hot Dry Rock Geothermal Reservoir at Fenton Hill, New Mexico. To calculate Q, we measure the P- and S-wave amplitudes as a function of distance and geometrical spreading effects, and match the relative attenuation to a function of the form exp (-1R/QV) using a least-squares regression technique. For undisturbed parts of the reservoir, we obtain values of Q on the order of 160 for P waves and from 170 to 150 for S waves. Using our method we are able to detect a decrease in the average Q due to extensive fracturing following heat extraction from the Fenton Hill reservoir. We have also been able to locate discrete large-scale fractures in the reservoir by noting regions characterized by a sudden change in signal amplitude, waveform or frequency content that cannot be explained by radiation pattern effects or increases in source-receiver separation. These localized attenuating regions in the Fenton Hill Hot Dry Rock reservoir are probably open fractures. (Author)

• Availability:
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• Corporate Authors:

  American Geophysical Union

  2000 Florida Avenue, NW
  Washington, DC  United States  20009-1277
• Authors:
  • Fehler, M
  • Pearson, C
• Publication Date: 1983-12-13

Media Info

• Pagination: p. 984
• Serial:
  • EOS Transactions
  • Volume: 64
  • Issue Number: 50
  • Publisher: American Geophysical Union
  • ISSN: 0096-3941

Subject/Index Terms

• TRT Terms: Amplitude; Crossheadings; Electromagnetic frequencies; Electromagnetic radiation; Fracture mechanics; Geological surveying; Granite; Least squares method; Presplitting; Seismicity; Transducers; Waveform analysis
• Uncontrolled Terms: Change; Fracture; Seismic investigations
• Old TRIS Terms: Cross hole; Subsurface explorations; Waveform
• Subject Areas: Geotechnology; Highways; I41: General Soil Surveys;

Filing Info

• Accession Number: 00381246
• Record Type: Publication
• Files: TRIS
• Created Date: Mar 30 1984 12:00AM