Fracture characterization and fracture-permeability estimation at the Underground Research Laboratory in southeastern Manitoba, Canada

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Authors:Paillet, F. L.
Author Affiliations:Primary:
U. S. Geol. Surv., Denver, CO, United States
Source:Reston, VA [Water-Resources Investigations - U. S. Geological Survey, No.WRI88-4009, 42p. Publisher: U. S. Geological Survey,], United States. ISSN: 0092-332X
Publication Date:1988
Note:In English. 34 refs.
Summary:Various conventional geophysical well logs were obtained in conjunction with acoustic tube-wave amplitude and experimental heat-pulse flowmeter measurements in two deep boreholes in granitic rocks on the Canadian shield in southeastern Manitoba. The objective of this study is the development of measurement techniques and data processing methods for characterization of rock volumes that might be suitable for hosting a nuclear waste repository. One borehole, WRA1, intersected several major fracture zones, and was suitable for testing quantitative permeability estimation methods. The other borehole, URL13, appeared to intersect almost no permeable fractures; it was suitable for testing methods for the characterization of rocks of very small permeability and uniform thermo-mechanical properties in a potential repository horizon. Epithermal neutron , acoustic transit time, and single-point resistance logs provided useful, qualitative indications of fractures in the extensively fractured borehole, WRA1. A single-point log indicates both weathering and the degree of opening of a fracture-borehole intersection. All logs indicate the large intervals of mechanically and geochemically uniform, unfractured granite below depths of 300 m in the relatively unfractured borehole, URL13. Some indications of minor fracturing were identified in that borehole, with one possible fracture at a depth of about 914 m, producing a major acoustic waveform anomaly. Comparison of acoustic tube-wave attenuation with models of tube-wave attenuation in infinite fractures of given aperture provide permeability estimates ranging from equivalent single-fractured apertures of less than 0.01 mm to apertures of > 0.5 mm. One possible fracture anomaly in borehole URL13 at a depth of about 914 m corresponds with a thin mafic dike on the core where unusually large acoustic contrast may have produced the observed waveform anomaly. No indications of naturally occurring flow existed in borehole URL13; however, flowmeter measurements indicated flow at < 0.05 L/min from the upper fracture zones in borehole WRA1 to deeper fractures at depths below 800 m. (Author 's abstract)
Subjects:Crystalline rocks; Distribution; Engineering geology; Fractures; Geologic hazards; Ground water; Interpretation; Movement; Permeability; Radioactive waste; Rock mechanics; Site exploration; Thermomechanical properties; Underground storage; USGS; Waste disposal; Weathering; Well-logging; Canada; Manitoba; Pinawa Manitoba; Underground Research Laboratory; Western Canada; Materials, properties; Southeastern Manitoba
Coordinates:N500000 N503000 W0953000 W0961000
Record ID:1988054902
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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