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Document Type

Open Access

Degree Program

Geosciences

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2009

Month Degree Awarded

February

Keywords

discrete element method models, poroelastic models, deformation

Abstract

Cementation is known to significantly influence the mechanical and hydrologic properties of granular porous media by increasing the stiffness of the elastic response to stress and reducing permeability. The relationship between the changes in cementation and changes in permeability are well documented in literature. However, limited quantitative data exists on the relationship between changes in the amount of cementation and changes in the mechanical response of granular media. The goal of this research is to quantify the effects of cementation on the mechanical properties of granular porous media at the meso-scale and investigate the influence of the competing roles of mechanical and hydrologic properties on fluid flow and deformation at the macro-scale. To accomplish this goal, we developed a multiple scale approach that utilizes the parameterization control of meso-scale Discrete Element Method (DEM) models and the ability to couple fluid flow and solid deformation physics with macro-scale poro-elasticity models.

At the meso-scale, a series of DEM models are designed to simulate biaxial tests of variably cemented sandstone in order to investigate the effects of cementation on the elastic and inelastic response of the porous media. The amount of cementation in the DEM model is quantified using a bond to grain ratio (BGR). The BGR is the number of bonds (the bonds represent the cement) divided by the number of grains in each model. The BGRs of the DEM models correlate to BGRs of natural samples and allow constraint of the percent cementation in the DEM models. A decrease in BGR from 2.25 to 1.00 results in a two fold decrease in shear modulus. The resulting shear moduli from the DEM models are used as input properties into two dimensional, axial symmetric poroelastic models of an isotropic confined aquifer. The poroelastic models address the implications of changes in mechanical properties and hydrologic properties on large scale fluid removal and deformation as well as address the importance of the competing roles of hydrologic and mechanical properties.

First Advisor

David F. Boutt

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