Geophysical well-log analysis of fractured granitic rocks at Atikokan, Ontario, Canada

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Authors:Paillet, F. L.; Hess, H. E.
Author Affiliations:Primary:
U. S. Geol. Surv., Lakewood, CA, United States
Source:Reston, VA [Water-Resources Investigations - U. S. Geological Survey, No.WRI87-4154, 36p. Publisher: U. S. Geological Survey,], United States. ISSN: 0092-332X
Publication Date:1987
Note:In English. 24 refs.
Summary:Two boreholes, drilled to approximate depths of 750 and 1,260 m in a granitic intrusion located near Atikokan, Ontario, were studied by obtaining a full suite of conventional borehole geophysical logs. In addition, selected intervals in these boreholes were logged with a borehole acoustic televiewer that produces a high-resolution image of the borehole wall, an acoustic waveform-logging system using 34-kiloHertz magnetostrictive and 5-kiloHertz sparker sources, and a highly sensitive heat-pulse flowmeter. Emphasis was on identifying and characterizing fracture zones that represent groundwater conduits in deeper portions of the granite, and on characterizing the properties of the largest intervals of unfractured granite. Major fracture zones were indicated by correlating geophysical log anomalies detected on the suite of conventional logs (unpublished data from Atomic Energy of Canada). However, several other anomalies, were identified as mafic intrusions of approximately the same thickness as major fracture zones. Geophysical log anomalies were compared for all major fracture zones that could serve as significant groundwater conduits, and fracture zone permeability is estimated on the basis of acoustic tube-wave attenuation in these intervals. Acoustic televiewer logs obtained at depths below 1,000 m in the deeper well indicate that most of the few fractures identified on core at these depths do not remain open enough under in situ conditions to produce detectable anomalies in acoustic refraction. Flowmeter data indicate that some groundwater circulation occurs in the upper portion of both boreholes. Water in the shallower of the two holes was observed to flow at 2.0 L/min; most of this flow entered the borehole at a depth < 25 m, and no flow occurred below a depth of 100 m. Downflow at rates < 0.5 L/min was determined to enter the deeper borehole within 20 m of the surface, and to exist at various fractures down to a depth of 250 m. (Author 's abstract)
Subjects:Acoustical logging; Applications; Electrical logging; Engineering geology; Fractures; Granites; Ground water; Igneous rocks; Plutonic rocks; Radioactive waste; Radioactivity; Site exploration; Surveys; Underground storage; USGS; Waste disposal; Well-logging; Atikokan Ontario; Canada; Canadian Shield; Eastern Canada; Great Lakes region; North America; Ontario; Rainy River District Ontario
Coordinates:N485200 N485500 W0924200 W0924700
Record ID:1988035199
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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