Comparison of Borehole Flow Measurements Obtained by Heat Pulse Flowmeter and Dilution Logging in a Fractured Bedrock Aquifer

We compare flow measurements made under ambient and pumping conditions in a bedrock borehole using high-resolution flow (heat pulse flowmeter) and fluid column dilution (repeat conductivity profiles after brine emplacement) methods. A second round of brine emplacement was avoided by using the fluid column conditions at the end of the ambient part of the dilution experiment as the initial condition for the pumping part of the dilution experiment. The estimates of flow by both methods yielded results that were in close agreement. The dilution method yielded direct estimates of flow based on the movement of interfaces, but logistics would have required the experiment to be repeated at two different pumping rates for most accurate results. The flowmeter yielded interval-averaged estimates of flow that agreed with the dilution results, but there was scatter of as much as 100% among the individual flow measurements. The flowmeter also required measurements under more than one pumping rate, and this was logistically much easier to accomplish than for the dilution experiment. We conclude that the methods are largely equivalent, with offsetting advantages and disadvantages for each method such that best results would be obtained using both methods in the same borehole.