Application of Advanced Geophysical Logging Methods in the Characterization of a Fractured-Sedimentary Bedrock Aquifer, Ventura County, California
by John H. Williams, John W. Lane, Jr., Kamini Singha, and F. Peter Haeni
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 00-4083
ABSTRACT
An integrated suite of advanced geophysical logging methods was used to characterize the
geology and hydrology of three boreholes completed in fractured-sedimentary bedrock in Ventura
County, California. The geophysical methods included caliper, gamma, electromagnetic induction,
borehole deviation, optical and acoustic televiewer, borehole radar, fluid resistivity, temperature,
and electromagnetic flowmeter. The geophysical logging 1) provided insights useful for the overall
geohydrologic characterization of the bedrock and 2) enhanced the value of information collected
by other methods from the boreholes including core-sample analysis, multiple-level monitoring, and
packer testing.
The logged boreholes, which have open intervals of 100 to 200 feet, penetrate a sequence of
interbedded sandstone and mudstone with bedding striking 220 to 250 degrees and dipping 15 to 40
degrees to the northwest. Fractures intersected by the boreholes include fractures parallel to bedding
and fractures with variable strike that dip moderately to steeply. Two to three flow zones were
detected in each borehole. The flow zones consist of bedding-parallel or steeply dipping fractures or
a combination of bedding-parallel fractures and moderately to steeply dipping fractures. About 75
to more than 90 percent of the measured flow under pumped conditions was produced by only one of
the flow zones in each borehole.
Citation: Williams, John H., Lane, John W., Jr., Singha, Kamini, and Haeni, F. Peter, 2002, Application of Advanced Geophysical Logging Methods in the Characterization of a Fractured-Sedimentary Bedrock Aquifer, Ventura County, California: U.S. Geological Survey Water-Resources Investigations Report 00-4083, 28 p.
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