Importance of fracture deformation throughout hydraulic testing under in situ conditions

Abstract

In this work, we propose a hydro-mechanical simulation model to study the strong interaction of fluid flow and fracture deformation under in-situ stress conditions. The general model is reduced under physics-based assumptions to provide an efficient numerical approach for inverse analysis of experimental studies and is applied to experimental field data obtained from hydraulic tests conducted at the Grimsel Test Site (GTS), Switzerland. The present set of hydro-mechanical measurement data provides not only valuable information about the transient pressure and flow evolution but also the transient change of fracture deformation. We aim to introduce a strongly-coupled hydro-mechanical model to numerically characterize the fractured reservoir based on experimental data below the limit of hydraulically induced irreversible changes of the reservoir’s properties. Insights into the leading mechanisms of flow processes throughout hydraulic testing under in-situ conditions are then gained by best numerical fits of the measurement data. Based on the experimental and numerical findings, this study emphasizes the importance of a consistent consideration of local and non-local fracture deformation throughout inverse analysis of hydraulic testing data to a) better understand hydro-mechanical flow processes in fractured reservoirs and b), to increase the estimation quality of hydraulic properties of tested fractures.