Measuring well hydraulic connectivity in fractured bedrock using periodic slug tests

•Periodic slug tests were conducted in an isolated fracture.•A computer controlled winching system produces clear observable signals.•The phase shift and attenuation of observations signals were used to estimate T and S.•Periodic tests appear to be more sensitive to local heterogeneity than traditional tests.

SummaryPeriodic hydraulic experiments were conducted in a five-spot well cluster completed in a single bedding plane fracture. Tests were performed by using a winch-operated slug (submerged solid cylinder) to create a periodic head disturbance in one well and observing the phase shift and attenuation of the head response in the remaining wells. Transmissivity (T) and storativity (S) were inverted independently from head response. Inverted T decreased and S increased with oscillation period. Estimated S was more variable among well pairs than T, suggesting S may be a better estimator of hydraulic connectivity among closely spaced wells. These estimates highlighted a zone of poor hydraulic connection that was not identified by a constant rate test conducted in the same wells. Periodic slug tests appear to be a practical and effective technique for establishing local scale spatial variability in hydraulic parameters.