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High-resolution flow logging for hydraulic characterization of boreholes and aquifer flow zones at contaminated bedrock sites

Williams, J.H., jhwillia@usgs.gov, U. S. Geological Survey, 425 Jordan Road, Troy, NY 12180 United States
Johnson, C.D., U. S. Geological Survey, 11 Sherman Place, Storrs, CT 06269 United States
Paillet, F.L., University of Maine, 111 Bryand Global Science Center, Orono, ME 04469 United States

Abstract

In the past, flow logging was largely restricted to the application of spinner flowmeters to determine flow-zone contributions in large-diameter production wells screened in highly transmissive aquifers. Development and refinement of tool-measurement technology, field methods, and analysis techniques has greatly extended and enhanced flow logging to include the hydraulic characterization of boreholes and aquifer flow zones at contaminated bedrock sites. State-of-the-art in flow logging will be reviewed, and its application to bedrock-contamination investigations will be presented. In open bedrock boreholes, vertical flows are measured with high-resolution flowmeters equipped with flexible rubber-disk diverters fitted to the nominal borehole diameters to concentrate flow through the measurement throat of the tools. Heat-pulse flowmeters measure flows in the range of 0.05 to 5 liters per minute, and electromagnetic flowmeters measure flows in the range of 0.3 to 30 liters per minute. Under ambient and low-rate stressed (either extraction or injection) conditions, stationary flowmeter measurements are collected in competent sections of the borehole between fracture zones identified on borehole-wall images. Continuous flow, fluid-resistivity, and temperature logs are collected under both sets of conditions while trolling with a combination electromagnetic flowmeter and fluid tool. Electromagnetic flowmeters are used with underfit diverters to measure flow rates greater than 30 liters per minute and suppress effects of diameter variations while trolling. A series of corrections are applied to the flow-log data to account for the zero-flow response, bypass, trolling, and borehole-diameter biases and effects. The flow logs are quantitatively analyzed by matching simulated flows computed with a numerical model to measured flows by varying the hydraulic properties (transmissivity and hydraulic head) of the flow zones. Several case studies will be presented that demonstrate the integration of flow logging in site-characterization activities to: 1) delineate aquifer flow zones, estimate zone transmissivity and hydraulic head, and conceptualize the hydrogeologic framework; 2) evaluate cross-connection effects and determine flow-zone contributions to water-quality samples from open boreholes; and 3) design discrete-zone hydraulic tests and monitoring-well completions.


Final copy as submitted to the American Geophysical Union for publication as: Williams, J.H., Johnson, C.D., and Paillet, F.L., 2004, High-resolution flow logging for hydraulic characterization of boreholes and aquifer flow zones at contaminated bedrock sites: Eos Trans. American Geophysical Union, 85(17), Jt. Assem. Suppl., Abstract NS23A-07.


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