Identifying hydraulically conductive fractures with a slow-velocity borehole flowmeter

Abstract

The U.S. Geological Survey used a recently developed heat-pulse flowmeter to measure very slow borehole axial water velocities in granitic rock at a site near Lac du Bonnet, Manitoba, Canada. The flowmeter was used with other geophysical measurements to locate and identify hydraulically conducting fractures contributing to the very slow vertical water flow in the two boreholes selected for study. The heat-pulse flowmeter has no moving parts and operates on the tag–trace principle. It is an improved version of the flowmeter developed by the Water Research Centre in England in 1975. The U.S. Geological Survey's heat-pulse flowmeter has a flow-measuring range in water of 0.06–6 m/min, and can resolve velocity differences as slow as 0.01 m/min. This is an order of magnitude slower than the stall speed of spinner flowmeters. The flowmeter is 1.16 m long and 44 mm in diameter. It was calibrated in columns of 76 and 152 mm diameter, to correspond to the boreholes studied. The heat-pulse flowmeter system is evaluated, and problems peculiar to the measurement of very slow axial water velocities in boreholes are discussed. Key words: flowmeter, borehole flow, low flow, borehole geophysics.

Hydrogeologic characterization of six sites in southeastern Minnesota using borehole flowmeters and other geophysical logs

“…High-resolution borehole flowmeters, such as the heat-pulse (HPFM; Hess, 1986;Paillet and Crowder, 1996) and the electromagnetic flowmeter (EMFM; Molz and Young, 1993;Molz and others, 1994), can be used to determine the permeability of intervals intersecting open intervals of boreholes. In the simplest situations, flow profiles indicate intervals where flow enters the borehole under a given hydraulic condition.…”

Basalt features observed in outcrops, cores, borehole video imagery and geophysical logs, and basalt hydrogeologic study at the Idaho National Engineering Laboratory, Eastern Idaho

“…(Young, 1992). Spinner flowmeters are available that can measure vertical borehole water velocities of 2 m/min (7 ft/min) and greater, and some spinners have been made with stall speeds as slow as 0.6 m/min (2 ft/min) although many geologic formations have slower flow rates (Hess, 1986). This relationship is:…”

“…The intersection of the extended line to the axis is done to obtain an add-on constant related to, but not always equal to the stall speed. This is done by adding the intercept value to the cps-cable speed relationship: borehole diameter (mm) (Hess, 1986). The "785" arises from rc/4 in calculating the crosssectional area of the borehole.…”

“…Very slow borehole fluid velocities of a few meters per day have been measured by using tracer techniques (Hess, 1986). However, the use of radioactive solutions in groundwater is now subject to strict regulations, brine solutions are useful only in fresh water, and both techniques are subject to considerable measurement errors caused by the differences in density between the trace solution and the borehole fluid (Hess, 1986). Both Barraclough and others (1965) and Morris and others (1964) have done a large number of wells in various locations around the site.…”

“…The thermal flowmeter used by Morin and others had a inflatable packer system which served as a flow concentrator, channeling flow from a larger cross-sectional area to a smaller one and increasing the sensitivity of the instrument to very slow fluid velocities . Some heatpulse flowmeters have a useful flow-measuring range of 0.06 to 10 m/min (0.2 to 33 ft/min) (Hess, 1986).…”