An accurate knowledge of the engineering properties of rocks is crucial for a variety of geomechanical problems, ranging from wellbore stability to failure in rock slopes, underground excavations, and crustal faults. While strength and deformation properties are usually obtained from a limited number of in situ and/or laboratory tests, their determination is invariably affected by considerable heterogeneities. Such lack of homogeneity impacts engineering conclusions at all length scales and requires appropriate theoretical and computational tools. Advanced numerical modeling represents a useful tool to explore how mechanical processes interact across length scales. Considerable advances in this area have been based on Finite Element computations, where heterogeneities can be incorporated both at sample and site scales. Nevertheless, to capture realistically the path-dependent response of geomaterials, continuum formulations tend to be characterized by a large number of parameters. If such constants lack clear connections with measurable attributes (e.g., grain size and sorting), their calibration becomes poorly constrained. Furthermore, the tendency of rock samples to undergo strain localization processes further prevents the validation and/or implementation of continuum models, requiring a direct link between strain localization and microstructural attributes. More importantly, the fluid flow or permeability in granular rocks is coupled with the compressibility and strain localization. The importance of this property mainly emerges in petroleum industry for oil and gas extraction productivity estimations, performance forecasting, reservoir pressure maintenance and compaction and subsidence studies. In other words, the compressibility of the granular rock plays an important role on the hydraulic conductivity of the reservoirs while the reservoir depletion increases the stress carried by the load-bearing grain framework of the reservoir rock. This process triggers micron-scale deformation mechanisms such as microcrack growth and closure, cement breakage, grain rotation and sliding, and crystal plasticity in clay and mica grains. As a result, fully understanding the linkage between all these micro-processes and the macroscopic deformation response and the strain localization as well as the concurrent permeability evolution is critical and many researchers have focused on this topic.Several researchers have investigated experimentally the effect of pressure and stress path on the compaction and the coupled permeability evolution but yet a general correlation to predict the compaction and permeability change under different stress paths is missing. Also a number of coupled Hydrologic-Mechanical models have been developed by some researchers in order to analyze the flow-deformation processes during injection/extraction of fluids in granular rocks. The key components of these models are permeability functions and their coupling with porosity changes. While mechanical models are rather advanced, hydraulic models in these studies tend to ignore other components other than porosity and resort to complex empirical functions. This thesis focuses on the formulation of a continuum based permeability prediction model, which incorporates the effects of porosity change as well as grain breakage and cement damage in granular rocks under different loading paths. For this purpose, Breakage Mechanics theory has been adopted for mechanical analysis of granular materials which provides the change of porosity as well as the evolution of the grain size distribution. Thereafter, such outputs are used in a permeability model for granular materials called Kozeny model in order to predict the permeability reduction under loading. In addition, a discrete element based model called Lattice Discrete Particle Model (LDPM), which has been proposed recently to simulate quasi-brittle materials at the scale of the major heterogeneities (length scale of coarse grains) is modified for simulation of granular rocks and the results are verified against experimental data. Also, strain localization formation under different localization regimes is studied.

Last modified

• 02/20/2018

Creator

• Shiva Esna Ashari Esfahani

DOI

• https://doi.org/10.21985/N2JT3W

Subject

• Civil and Environmental Engineering

Keyword

• Civil Engineering

Date created

• 2016-01-01

Resource type

• Dissertation

Rights statement

• In Copyright