The Analysis of Pulse Interference Tests Conducted in a Fractured Rock Aquifer Bounded by a Moving Free Surface

Pulse interference tests are a common method of determining the hydraulic properties such as the transmissivity and storativity of a geological formation between two wells. An analytical model is presented for the analysis of pulse interference tests conducted in a fractured porous medium with connection to a free surface boundary at the water table. The solution is applicable to open borehole pulse interference tests due to the accommodation of multiple horizontal fractures intersecting each well bore and a connection from the top horizontal fracture to a free surface boundary. Wellbore storage is included at the source and observation wells using an approximate superposition technique. The water table is formulated as a free surface boundary accompanied by delayed drainage from the vertical fractures, which is modelled using an expression based on equivalent porous media.  The solution is derived using the Laplace transform method and evaluation of the solution is performed by numerical inversion using the Talbot algorithm. An approach is presented for the determination of a unique value of specific yield based on a particular pair of transmissivity and vertical hydraulic conductivity values. Although unique values for storativity and specific storage are not determined using this method, a sensitivity analysis shows that unique values for transmissivity and vertical hydraulic conductivity are predicted over a range of realistic values for storativity and specific storage. Field examples are presented to illustrate the application of the model and its capability to estimate unique values of specific yield even in fractured rock settings with relatively low vertical permeability.