Time: Tuesday, September 12, 2023 at 10-11:30 am
Place: Guttenberghaus, Feistmantelstrasse 4, 1180 Vienna, seminarroom 03 (SR-03)
Shale is known to exhibit significant creep across spatiotemporal scales. In this work, we perform indentation and triaxial creep tests on organic-rich Woodford shale and show that the measured creep responses at the nanometer and millimeter scales are statistically correlated in the sense that the indentation creep tests can be used to predict the triaxial creep response. The link between the two extreme scales is facilitated by an elasto-viscoplastic constitutive model based on critical state theory. Even though this constitutive model contains several material parameters, only the elastic modulus and viscosity play a major role in statistically correlating the creep responses at the two scales. Given that shale is commonly represented as a transversely isotropic material, we conduct indentation and triaxial creep tests in both bed-normal (BN) and bed-parallel (BP) directions on the rock samples. For the shale that was tested, the creep responses at the nanometer and millimeter scales are statistically correlated in the BN direction where the rock is weaker. However, the creep deformations at the two scales in the BP direction, where the rock is stronger, are significantly smaller than in the BN direction, and are not as strongly correlated. Nevertheless, the results of this study suggest that in addition to its inherent heterogeneity, shale can also exhibit strongly anisotropic creep responses.
BIOGRAPHY: Ronaldo Borja works in theoretical and computational solid mechanics, geomechanics, and geosciences. His research includes the development of multi-scale discontinuity framework for crack and fracture propagation utilizing the strong discontinuity and extended finite element methods, and solution techniques for multi-physical processes. He is the author of a textbook entitled Plasticity Modeling & Computation published by Springer and serves as editor of two leading journals in his field, the International Journal for Numerical and Analytical Methods in Geomechanics and Acta Geotechnica. Ronaldo Borja is the recipient of the 2016 ASCE Maurice A. Biot Medal for his work in computational poromechanics.