Applications of the Thermal-Pulse Flowmeter in the Hydraulic Characterization of Fractured Rocks

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Abstract
The U.S. Geological Survey has developed a thermal-pulse flowmeter capable of detecting borehole flows to as small as 0.04 L/min. This new flowmeter provides much greater sensitivity to slow vertical flow than that available using conventional spinner flowmeters. This paper describes five applications of the thermal-pulse flowmeter in the characterization of the hydrology of fractured rocks. These applications include measurement of flows in boreholes driven by ambient hydraulic-head differences, identification of fractures contributing flow during production tests, inference of fracture interconnections during aquifer tests, interpretation of water-quality contrasts in boreholes, and identification of fractures affected by hydraulic stimulation procedures. Each of the five applications is illustrated by specific examples selected from ongoing research activities at various fracture hydrology study sites.