Hydrogeologic Characterization of Six Sites in Southeastern Minnesota UsingBorehole Flowmeters and Other Geophysical Logs

摘要

Caliper, gamma, normal resistivity, fluid column temperature and resistivity, andteleviewer logs were combined with borehole flow logs to infer the nature of water-producing intervals in six observation boreholes at sites in southeastern Minnesota. Flow profiles were obtained with either the electromagnetic or heat-pulse flowmeters, depending upon equipment availability at the time of logging. Gamma and resistivity logs were used to determine the stratigraphic position of open intervals in each of the boreholes. Water-producing intervals identified using the flowmeter logs were characterized as permeable coarse-clastic beds, solution openings along bedding planes, fractures, or karstic horizons on the basis of gamma, caliper, and televiewer logs. Flow log interpretation theory demonstrates that the hydraulic head and transmissivity of water-producing intervals intersecting an open borehole can be estimated if flow logs are obtained under two different quasi-steady conditions, and if the difference in open-borehole water level between the two conditions can be measured. If logistical conditions prevent flow logging under more than one condition, water-producing zones can be identified, but relative transmissivity values cannot be estimated.