Comparison of drilling reports and detailed geophysical analysis of ground-water production in bedrock wells
- Geological Survey, Denver, CO (United States)
- Walt Banyan Drilling, Inc., Oakhurst, CA (United States)
The most extensive data base for fractured bedrock aquifers consists of drilling reports maintained by various state agencies. They investigated the accuracy and reliability of such reports by comparing a representative set of reports for nine wells drilled by conventional air percussion methods in granite with a suite of geophysical logs for the same wells designed to identify the depths of fractures intersecting the well bore which may have produced water during aquifer tests. Production estimates reported by the driller ranged from less than 1 to almost 10 gallons per minute. The moderate drawdowns maintained during subsequent production tests were associated with approximately the same flows as those measured when boreholes were dewatered during air percussion drilling. They believe the estimates of production during drilling and drawdown tests were similar because partial fracture zone dewatering during drilling prevented larger inflows otherwise expected from the steeper drawdowns during drilling. The fractures and fracture zones indicated on the drilling report and the amount of water produced by these fractures during drilling generally agree with those identified from the geophysical log analysis. Most water production occurred from two fractured and weathered zones which are separated by an interval of unweathered granite. The fractures identified in the drilling reports show various depth discrepancies in comparison to the geophysical logs, which are subject to much better depth control. However, the depths of the fractures associated with water production on the drilling report are comparable to the depths of the fractures shown to be the source of water inflow in the geophysical log analysis.
- OSTI ID:
- 7239801
- Journal Information:
- Ground Water; (United States), Journal Name: Ground Water; (United States) Vol. 32:2; ISSN GRWAAP; ISSN 0017-467X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effects of longwall mine subsidence on overlying aquifers in western Pennsylvania. Open file report 26 September 1979-25 January 1984
Conjunctive use of air photo interpretation and geophysics to evaluate fractured bedrock aquifers
Related Subjects
540210* -- Environment
Terrestrial-- Basic Studies-- (1990-)
58 GEOSCIENCES
580000 -- Geosciences
FLUID FLOW
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
GRANITES
GROUND WATER
HYDRAULIC CONDUCTIVITY
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SURVEYS
WATER