Enhanced estimate of fracture network dimensions by injection of non-Newtonian fluids

Abstract

Lugeon tests, also known as water pressure tests, are widely used to estimate the transmissivity of rock-fracture networks and are considered standard testing for grouting of dam foundations. The Lugeon test consists of injecting water into an isolated borehole section intersecting several fractures and monitoring water pressure and flow rate over time to estimate the rock fractures’ transmissivity. An average fracture aperture for the whole section is then estimated from the transmissivity value, which is used for selecting the appropriate grout mix. However, the current procedure does not provide any information on the variability in aperture sizes within the investigated rock interval. This paper presents a new approach for performing Lugeon testing that allows for providing a probabilistic distribution of fracture apertures by injecting bio-degradable non-Newtonian fluids at different pressures/flow rates. The theoretical framework demonstrating the ability to estimate the dimensions of multiple fractures, in parallel and in series, from non-Newtonian fluid injection tests is presented. Then, experimental results on different combinations of simple fractures, made of parallel plates, are used to validate the derived model and evaluate its performance.