Thermal flowmeter modification for the addition of a packer and pump

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Abstract
Measuring water movement in boreholes has achieved greater hydrogeologic importance in recent years. Most flowmeters can measure flows greater then 180 cm/min, with some specialized spinner flowmeters with stall velocities as low as 14 cm/min. However, in many cases the injection or removal of water from a well may not be acceptable. For example, groundwater contamination may prohibit ground-surface discharge of borehole fluids, borehole stability may be of concern in uncased boreholes, and cost may limit the use of a pump. Two geophysical logging tools have been developed to measure slow water velocities in boreholes: the thermal-pulse flowmeter (TFM), and the electromagnetic flowmeter. The TFM was used in this study. Measurement accuracy was increased by nearly one order of magnitude by outfitting the thermal-pulse flowmeter (TFM) with an inflatable packer. To accurately measure slow water velocities in boreholes greater than 15 cm diameter, it is necessary to divert borehole fluids through the TFM by inflating a packer. During calibration it was noted that the TFM`s accuracy decreased as the borehole diameter increased. With the packer inflated, the TFM has a useful flow measurement range of 0.08 to 15 l/min (with flow velocities of 0.24 {+-} 0.012 cm/min to 45.7 {+-}more » 0.61 cm/min, respectively, in 20-cm-diameter pipe), compared to 0.8 to 57 l/min for a packerless TFM. A computer interface was added to the TFM to provide a real-time graphical display of the differential voltage output from the TFM, a running mean and standard deviation of the pulse-response time, and mean flow rate and velocity based on calibration curve fits.« less

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