Li, Aibing2020-06-04May 20202020-05May 2020Portions of this document appear in: Wang, Yang, De-Hua Han, Hui Li, Luanxiao Zhao, Jiali Ren, and Yonghao Zhang. "A comparative study of the stress-dependence of dynamic and static moduli for sandstones." Geophysics 85, no. 4 (2020): MR179-MR190. And in: Wang, Yang, Hui Li, Abhijit Mitra, De-Hua Han, and Teng Long. "Anisotropic strength and failure behaviors of transversely isotropic shales: An experimental investigation." Interpretation 8, no. 3 (2020): SL59-SL70.https://hdl.handle.net/10657/6716Understanding the differences between static and dynamic elastic properties of underground rocks is essential for the successful hydraulic fracturing. For heterogeneous porous sedimentary rocks, static elastic properties can differ a lot from dynamic elastic properties even at the same stress level. We investigate the stress dependence of dynamic and static mechanical properties through laboratory measurements and micro-mechanical analysis on sandstone and shale samples. In general, static tests respond to the superpositions of the elastic, viscoelastic, and non-elastic properties along with a stress increment, whereas dynamic tests, with more than two orders of magnitude smaller strain amplitude, only reflect the elastic properties of rocks. As a result, the dynamic modulus is characteristically higher than the static modulus at almost any stress level, whereas the static Poisson’s ratio expresses a lower value at low stress and higher value at high stress in contrast to the dynamic Poisson’s ratio. The experimental results also suggest that intrinsic beddings of the anisotropic shales would have significant impacts on dynamic and static properties. The rock is generally stiffer in the bedding-parallel direction than in the bedding-normal direction. Considering the strong stress dependence of static properties, we propose two ways to determine static elasticity in the stress-strain curves: uniaxial load-unload experiments with a series of minor stress cycles and increasing-amplitude cyclic loading and unloading experiments. The first one offers an easy approach to investigate static properties of the rock matrix without microstructural effects. The second one documents the evolution of static elastic properties in great detail by considering the in-situ stress conditions and emphasizes that there exists a relatively elastic region with similar static properties regardless of the numbers of loaded or unloaded stress cycles. The new approach is more effective than the traditional one, which is limited to the linear elastic region of the loading stress-strain curves.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Rock mechanicsRock physicsDynamic propertiesStatic propertiesElasticityFrictional slips2020-06-04Thesisborn digital