Emerging Scientists Session
Predicting the Hydro-Mechanical behavior of fractured rocks: the importance of estimating a representative Biot coefficient
- Dr. Silvia De Simone
- Spanish National Research Council
Biography
Silvia De Simone is a researcher at the Institute of Environmental Assessment and Water Research of the Spanish National Research Council (IDAEA-CSIC, Spain).
She obtained her Bachelor’s and Master's degrees in Civil and Environmental Engineering at the University of Naples Federico II (Italy), and her PhD in Geotechnical Engineering at the Polytechnical University of Catalonia UPC (Spain). As a postdoctoral researcher, she was enrolled in the Subsurface CO2 group at Imperial College London (ICL, UK) and at the Geosciences Rennes Institute of the French National Centre for Scientific Research (CNRS, France).
Her research focuses on quantitative hydrogeology and computational geomechanics, with special emphasis on coupled Thermo-Hydro-Mechanical (THM) processes occurring in deep fractured and porous formations during the development of geo-energy activities.
Introduction of the Lecture
Understanding and predicting the hydro-mechanical (HM) behavior of subsurface porous and fractured formations is key to a number of engineering applications, including fluid injection/extraction, construction/excavation, geo-energy production and deep geological disposal. The interaction between fluid pressure, deformations and stresses is particularly affected by the subsurface heterogeneity, which may lead to non-intuitive responses, such as effective stress reduction and pressure increase during fluid extraction. While the impact of large-scale heterogeneities is acknowledged in most studies and modeling efforts, the presence of heterogeneities at smaller scales cannot be included in reservoir-scale models and it must be encompassed into equivalent properties assigned to uniform materials.
In this talk, I will focus on the Biot effective stress coefficient, a central property determining the HM behavior of fluid-saturated geological media. When not simply assumed as equal to 1, this coefficient is estimated experimentally at the laboratory sample-scale or analytically through expressions valid for isotropic homogeneous materials. However, these approaches are not able to estimate a representative equivalent coefficient for fractured rocks, which are strongly anisotropic and prone to sample-size effects, with fracture lengths spanning several orders of magnitudes from millimeters up to hundreds of meters. After presenting a theoretical framework to quantify an equivalent Biot coefficient for a fractured rock mass from the properties of both the porous intact rock and the discrete fracture network (DFN), I will analyze the variability of this coefficient with the DFN properties and discuss the implications for the rock upscaled HM behavior, in the context of natural processes and engineering applications.