High-resolution flowmeter log
High-resolution flowmeters that use heat-pulse and electromagnetic methods can measure extremely low vertical flow rates in boreholes. Conventional impeller flowmeters that are widely used in ground-water studies have a lower measurement limit of about 2 meters per minute, whereas the high-resolution flowmeters have lower measurement limits of less than 0.03 meters per minute. Flowmeters can be used to measure borehole flow under ambient as well as pumped conditions. Borehole-flow measurements made under ambient conditions can help to delineate transmissive fractures and other permeable zones and to indicate the direction of vertical hydraulic gradients; they also are useful in interpreting fluid-conductivity logs and borehole water-quality data. Borehole-flow measurements made under pumped conditions can be used to develop hydraulic-conductivity profiles of aquifers.