Investigation of the effects of fractured porous media on hydraulic tests - an experimental study at laboratory scale using single well methods

Abstract

In this paper, a study of detailed pneumatic tests at laboratory scale is presented. The study comprises two different test methods, which were conducted on an unsaturated fractured sandstone block of about I m 3 volume. First, a steady-state flow field with constant gas injection pressure and consequently constant gas flow rates was applied to the fractured sandstone block via a vertical borehole. The discharge of the injected gas was measured at the block surface. Second, a constant gas pressure was injected over the borehole and the transient pressure buildup was recorded at the block surface. It was the objective of the study to investigate the effects of the fractured porous system on pneumatic measurements and to provide an insight into processes occurring during flow and pressure buildup in fractured porous media. This is an essential prerequisite for a reliable validation of different modeling approaches, and it can further assist to improve techniques for the determination of the heterogeneity of hydraulic parameters in fractured porous media. The analysis of the distribution of the flow field and the temporal and spatial evolution of pressure buildup during the hydraulic tests shows that the direction and contribution of the flow field is highly depending on the spatial distribution and the characteristics of the fracture network as well as on the position of the observation points with respect to highly conductive structures. Finally, the introduced test methods are suitable tools for the characterization of the heterogeneous nature of fractured porous media and for the interpretation of the effects of the heterogeneous system on hydraulic tests. (C) 2004 Elsevier B.V. All rights reserved.