A New Model for Well Test Analysis in a Purely Fractured Medium

Abstract

In a porous medium the fiow conduits are small and a large number of conduiw are connected to the well. For this reason the medium appears to behave like a continuum on the scale of the well test, and volumetric averaging and continuum approximations are justified. On the contrary, in a fractured medium, only a small number of fractures may intersect the pumping well. These particular fractures will be stressed by a large gradient under well test conditions. Consequently, the early time behavior will be dominated by these fractures. The volumetrically averaged permeability does not control fiow in the vicinity of an active well. The individual fractures close to the well must be characterized in order to understand the well test behavior especially if the hydraulic parameters of these fractures are significantly different from the average values for the entire system. In the present study, a new analytical model is p r e posed for well test problems in fracture networks where the matrix is impermeable. The model accounts for the difference in the fiow regime around the active well from that of the system as a whole. The analytical solutions are presented in a series of type curves for ranges of dimensionless parameters. The fiow propreties of the fracture system can be determined by curve matching.