COMPARISON OF FLOWMETER ESTIMATES OF FRACTURE ZONE PERMEABILITY WITH CONVENTIONAL STRADDLE PACKER INJECTION TESTS
Frederick L. Paillet and Barbara A. Allen
U. S. Geological Survey
Denver, CO
Borehole flow profiling with recently developed high-resolution flowmeters has been proposed as an inexpensive alternative to conventional straddle packer testing of bedrock aquifers. Analyses of flowmeter measurements have been shown to give quantitative estimates of in situ permeability, but these analyses as reported in the literature are restricted by certain assumptions that may impact the reliability of the permeability estimates. We also show that the potential measurement error in flowmeter interpretations is a function of borehole specific capacity. The practical effects of these potential sources of error in flow profile interpretations are examined by comparing permeability profiles interpreted on the basis of U. S. Geological Survey heat-pulse flowmeter logs obtained during borehole pumping to permeability distributions given by the analysis of straddle packer isolation and injection tests. The flowmeter profiles and hydraulic test data were obtained in a set of 11 boreholes in the FSE borehole array at the Mirror Lake, New Hampshire research site. Borehole televiewer logs were used to identify from 20 to more than 50 apparently permeable fractures intersecting each borehole. Interval transmissivity values given by the straddle packer tests ranged from almost 10-4 to less than 10-9 m2/s. Relative inflow from each producing interval was normalized to an assumed net borehole pumping rate of 5 liters per minute, and showed a much closer correlation with hydraulic test data than other estimates of fracture permeability such as fracture density inferred from borehole image logs. Flowmeter data were used to generate interval averaged transmissivity distributions in each borehole by assigning a percent of total borehole inflow during quasi-steady pumping or recovery after pumping to specific intervals. The percent values were translated to units of transmissivity by multiplying the fractional inflow in each interval by the total aquifer tramsmissivity estimated from borehole production tests. In all 11 boreholes, the flow profile analysis consistently identified the most transmissive zones indicated by the straddle packer test results. The dependence of measured inflows on background aquifer conditions had only a minor effect on transmissivity estimates. The primary limitation on the flowmeter estimates of transmissivity was imposed by the dynamic range of flowmeter measurements. This limitation results from the range of flowmeter sensitivity from 0.05 to 10 liters per minute. Aquifer test conditions were usually adjusted to cause inflow from the most productive fractures to fall within the range of maximum flowmeter sensitivity, so that less productive intervals were not detected. Other error is attributed to measurement error or limited data obtained while monitoring water level during pumping. These results demonstrate that properly analyzed flowmeter data can give approximate By useful estimates of fracture zone transmissivity in open boreholes, and may be especially useful in identifying zones for long-term aquifer monitoring.Back to Table of Contents