Humidity Effects on Effective Elastic Properties of Rock: An Integrated Experimental and Numerical Study

Abstract

The surface energy of minerals increases due to a loss of humidity. In rocks this leads to strains without applying external stress (stress‐free strain) and affects the rocks' elastic response. We utilize finite element calculations on X‐ray micro‐CT images to analyze the extreme cases of surface energy contributions and no surface energy contributions for the small strain case. Including surface energy utilizing published surface energies of quartz significantly increases the simulated bulk modulus. Grain contacts are considered perfectly cemented and therefore do not contribute to this difference. Confining pressure is not applied in the experiment to estimate the impact of surface energy to avoid the effect of grain contact slippage due to different stress paths. In addition, we compare simulated moduli with experimentally determined parameters. In this case, we incorporate confining pressure in the experiment since grain contacts are not considered in the simulation. The main reason to use confining pressure in the experiment here is to close the grain contacts with a view that the resulting porosity reduction is negligible.

Hydraulic and Mechanical Impacts of Pore Space Alterations within a Sandstone Quantified by a Flow Velocity-Dependent Precipitation Approach

“…The calculated elastic rock properties of the initial microstructure based on the calibrated bulk and shear moduli for the grain phase are in good agreement with published laboratory data for the Bentheim sandstone [68][69][70][71][72]78,79] as demonstrated in Figure 8a. The growth of minerals within the pore space generally leads to a stiffening of the rock, what depends on the elastic properties of the precipitated phase, which is calcite in the present study.…”

“… ( a ) Absolute and percentual increases in bulk and shear moduli due to preferential precipitation at high flow velocity magnitudes (HFV, red), low flow velocity magnitudes (LFV, blue) and uniform alterations, independent of the fluid flow (black). Calculated elastic properties are in good agreement with published laboratory data [ 68 , 69 , 70 , 71 , 72 , 78 , 79 ]. ( b ) Stress distribution within the initial microstructure compared to the uniform and LFV alteration patterns.…”

Elastic properties of confined fluids from molecular modeling to ultrasonic experiments on porous solids

“…Another correlation between deformation and ultrasound propagation has been reported for water adsorp-tion on sandstones. A number of studies have reported a significant reduction of ultrasonic speeds, and/or increase of ultrasonic attenuation in vacuum-dry sandstones, upon imbibition of very small amounts of water [123][124][125][126][127][128][129][130][131][132][133][134]. This effect is not entirely understood, but is commonly attributed to the adsorption of water at very thin (likely nano-scale) contacts between adjacent grains.…”

High‐Precision Tracking of Sandstone Deformation From Micro‐CT Images

“…The recent development of micro‐Computed Tomography (micro‐CT) imaging technique provides high‐resolution, three‐dimensional representations of the pore geometry (Cnudde & Boone, 2013; Maire & Withers, 2014). Then, different physical processes are simulated based on the pore geometry to derive the rock effective properties (e.g., elasticity, permeability, electrical conductivity) (Andrä et al., 2013a, 2013b; Dai et al., 2021; Hossain et al., 2019; Madadi et al., 2009). The whole “image and compute” workflow is called Digital Rock Physics (DRP).…”

“…(e.g., elasticity, permeability, electrical conductivity) (Andrä et al, 2013a(Andrä et al, , 2013bDai et al, 2021;Hossain et al, 2019;Madadi et al, 2009). The whole "image and compute" workflow is called Digital Rock Physics (DRP).…”