Geophysical well-log analysis of fractured crystalline rocks at East Bull Lake, Ontario, Canada
Water-Resources Investigations Report
86-4052
By: Frederick L. Paillet and A.E. Hess
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Abstract
Various conventional geophysical borehole measurements were made in conjunction with measurements using a recently designed, low-frequency, acoustic-waveform probe and slow velocity flowmeter for characterization of a fractured mafic intrusion in southern Ontario, Canada. Conventional geophysical measurements included temperature, caliper, gamma, acoustic, single-point resistance, and acoustic televiewer logs. Hole stability problems prevented the use of neutron and gamma-gamma logs, because these logs require that a radioactive source be lowered into the borehole. Measurements were made in three boreholes as much as 850 m deep and penetrating a few tens of meters into granitic basement. All rocks within the mafic intrusion were characterized by minimal gamma radiation and acoustic velocities of about 6.9 km/sec. The uniformity of the acoustic velocities and the character of acoustic-waveform logs made with a conventional high-frequency logging source correlated with the density of fractures evident on televiewer logs. Sample intervals of high-frequency waveform logs were transformed into interpretations of effective fracture opening using a recent model for acoustic attenuation in fractured rocks. The new low-frequency sparker source did not perform as expected at depths below 250 m because of previously unsuspected problems with source firing under large hydrostatic heads. A new heat-pulse, slow velocity flowmeter was used to delineate in detail the flow regime indicated in a general way by temperature logs. The flowmeter measurements indicated that water was entering 2 of the boreholes at numerous fractures above a depth of 200 m, with flow in at least 2 of the boreholes exiting through large isolated fractures below a depth of 400 m. (Author 's abstract)
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | Geophysical well-log analysis of fractured crystalline rocks at East Bull Lake, Ontario, Canada |
| Series title | Water-Resources Investigations Report |
| Series number | 86-4052 |
| DOI | 10.3133/wri864052 |
| Edition | - |
| Year Published | 1986 |
| Language | ENGLISH |
| Publisher | U.S. Geological Survey, |
| Description | vi, 37 p. :ill., maps ;28 cm. |
| Google Analytic Metrics | Metrics page |