Hydraulic testing using a versatile straddle packer system for improved transmissivity estimation in fractured-rock boreholes

Abstract

Equipment has been developed for straddle packer testing in fractured-rock boreholes to conduct four types of tests (constant-head step tests, slug tests, constant-rate pumping tests, and recovery tests) without deflating the packers or adjusting equipment in the hole between tests. The goal is to achieve improved accuracy and precision in the determination of transmissivity (T). Water-pressure measurements are recorded using pressure transducers positioned above and below the test interval to identify connections from the test interval to the open borehole. Insights concerning the nature of test conditions are gathered with this equipment to assess errors related to deviations from assumptions inherent in the mathematical models used to determine T, including validation of the Darcian flow assumption, validation of slug test assumptions, cross-connection to the open borehole, inadequate borehole development, and dual permeability, thereby giving greater confidence in the calculated T values. When the errors indicated above are minimized, the constant-head step tests, slug tests and constant-rate pumping/recovery tests give nearly identical values. This multiple-test approach to fractured-rock studies increases confidence in test results, which is important when the goal is characterization of fracture networks for contaminant transport and fate assessment.