Laboratory Assessment of Colloidal Borescope and Heat-Pulse Flowmeters in Measuring Horizontal Flow in Fractured-Rock Simulators

The U.S. Geological Survey (USGS), at the request of the U.S. Army Environmental Command (USAEC), evaluated the capabilities of two borehole technologies to measure horizontal groundwater velocity and direction of flow in a parallel-plate fractured-rock simulator. A colloidal borescope flowmeter (HB) and a heat-pulse flowmeter (HH) were deployed in 4-inch and 6-inch inner-diameter simulated uncased wells that spanned 0.39- and 1.0-inch apertures with simulated groundwater velocities ranging from 2 to 958 feet per day. Measurements were made at the USGS Hydrologic Instrumentation Facility in the Hydraulics Laboratory and the Indianapolis office of the USGS Ohio-Kentucky-Indiana Water Science Center. Ten measurements were made with the HB in the 1-inch fracture aperture intersecting a 6-inch inner-diameter well. Seven measurements were made in the 0.39-inch fracture aperture intersecting a 4-inch inner diameter well and six were made in the 0.39-inch aperture 6-inch inner-diameter well. All measurements were within the velocity limits specified by the manufacturer. Results from these measurements using the HB can be found in the child item, 'Simulation Results for Colloidal Borescope Flowmeter'. Thirty-seven measurements were made with the HH in the 1-inch fracture aperture intersecting a 6 inch inner-diameter well. Eight measurements were made in the 0.39-inch fracture aperture intersecting a 4-inch inner diameter well and eight were made in the 0.39-inch aperture 6-inch inner-diameter well. The tested velocity range (2 to 958 ft/d) was similar to the range examined with the HB (34 to 958 ft/d) but exceeded the range suggested by the manufacturer (0.5-100 ft/d). Results from these measurements using the HH can be found in the child item, 'Simulation Results for Heat Pulse Flowmeter'. Seven measurements were made with the HB using various vertical placements relative to the fracture. Results from these vertical measurements using the HB can be found in the child item, 'Simulation Results for Vertical Placement of Colloidal Borescope Flowmeter'. The flowmeter systems used in this study are described in Bayless and others (2011), available at https://doi.org/10.1111/j.1745-6592.2010.01324.x.