About the hydro-mechanics of fractures and fracture networks in rocks

A comprehensive understanding of the physical properties of seismic waves (like dispersive phase velocities and/or attenuation) in fractured porous rocks is important in various fields like hydrocarbon and geothermal exploration/exploitation or water reservoir management. E.g. characterization of subsurface fluid flow requires accounting for hydromechanical coupling between fluid-pressure variations in conduits and related rock deformation.
In this presentation, modeling aspects and numerical simulations of a (weakly) compressible fluid along compliant hydraulic conduits, such as joints or fractures/fracture networks, are investigated. In order to efficiently describe transport processes andpressure diffusion through fractures with realistic geometries, i.e., characterized by high aspect ratios, a hybrid-dimensional approach is discussed and applied to harmonic pumping tests. Further, it will be shown that this modeling approach could be also applied to derive effective hydro-mechanical properties of reservoir rocks on the REV scale in an
efficient way. The consistent computational homogenization approach is therefore based on an extended Hill-Mandel macrohomogeneity condition. In the numerical studies, synthetic fracture networks in a periodic unit cell are stochastically generated representing typical reservoir scenarios. The resulting fluid-filled (fractured) poroelastic rock is numerically investigated by coupled Finite Element Methods. From the numerical results in the time-domain, we determine an effective pseudo-Skempton coefficient using computational homogenization approaches to replace the heterogeneous medium by a macroscopic, homogeneous viscoelastic substitute medium. The effective pseudo-Skempton coefficient captures two viscous attenuation phenomena, pressure diffusion
parallel to the fractures and leak-off perpendicular to the fractures. The two attenuation mechanisms are caused by viscous solid-fluid momentum interaction but are related to different inherent diffusion lengths and characteristic times (or frequencies). We discuss how the analysis of the effective pseudo-Skempton coefficient in frequency space provides a valuable tool for the analysis of interconnectivity of fracture networks and for the determination of aspect ratios of fractures in reservoirs.

Short Bio : Prof. Dr.-Ing. Holger Steeb got his Civil Engineefing Degree from University of Stuttgart, Germany in 1995. In 2002 he obtained his doctoral degree in Engineering from University of Stuttgart and in 2008, his habilitation degree in Mechanics, at Saarland University, Saarbrücken, Germany.
In 2004 he was a Post-Doc Fellow at Faculty of Applied Mathematics and Phisics, NTUA Athens, Greece and between 2002-2008 Academic Staff and Lecturer at Saarland, University, Saarbrücken.
From 2008-2009 he was an assistant Professore for Multi-Scale Mechanics at University of Twente, Enschede, The Netherlands. From 2009-2015 he was Professor for Continuum Mechanics, Ruhr-University Bochum, Germany and since 2015 he is Professor for Computational Continuum Mechanics, Institute of Mechanics, University of Stuttgart.