Constraints on Hydraulic Anisotropy from Periodic Pumping Tests Using a Double-Packer System

Periodic pumping tests are now being used to characterize subsurface hydraulic parameters owing to several advantages over conventional tests, for example, option of superposing periodic excitations on transients by the data processing in the frequency domain. We derive an analytical model of periodic pumping tests using a double-packer system to isolate an injection interval in a borehole penetrating either a confined or un-confined anisotropic aquifer. The model, which is apt for injectivity analysis and axial interference analysis, was evaluated by comparing it to previously presented solutions of the hydraulic diffusion equation considering appropriate limits regarding interval length, storage capacity of the interval, and the aquifer specific yield. The axial interference analysis constrains the ratio of axialto-radial hydraulic conductivity. Radial conductivity and specific storage are constrained by the injectivity analysis prescribing conductivity anisotropy ratios. The combination of the two analyses narrows down the range of estimated hydraulic properties. The application of our model to field data from a fault zone in crystalline rocks yields a subvertical conductivity at least 10 times greater than the horizontal value, which agrees qualitatively with the fault geometry. By proper choice of the pumping period, axial interference analysis can be used to not only assess the integrity of packers and their immediate surrounding but also to extend our understanding of subsurface features.