Geophysical well-log analysis of fractured crystalline rocks at East Bull Lake, Ontario, Canada

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Authors:Paillet, F. L.; Hess, A. E.
Author Affiliations:Primary:
U. S. Geol. Surv., Denver, CO, United States
Source:Reston, VA [Water-Resources Investigations - U. S. Geological Survey, No.WRI86-4052, 37p. Publisher: U. S. Geological Survey,], United States. ISSN: 0092-332X
Publication Date:1986
Note:In English. 22 refs.
Summary: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)
Subjects:Acoustical logging; Crystalline rocks; Deformation; Distribution; Engineering geology; Field studies; Fractures; Gabbros; Ground water; Igneous rocks; In situ; Instruments; Mafic composition; Mechanical properties; Migration; Patterns; Permeability; Plutonic rocks; Pollution; Radioactive waste; Radioactivity; Rock mechanics; Site exploration; Techniques; Testing; USGS; Waste disposal; Well-logging; Canada; Eastern Canada; Ontario; Chalk River region; Intrusive rocks; Southern Ontario
Record ID:1987052063
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from USGS product, Selected Water Resources Abstracts, Reston, VA, United States
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