Role of void space geometry in permeability evolution in crustal rocks at elevated pressure

Abstract

[1] A key consequence of the presence of void space within rock is their significant influence upon fluid transport properties. In this study, we measure changes in elastic wave velocities (P and S) contemporaneously with changes in permeability and porosity at elevated pressure for three rock types with widely different void space geometries: a high-porosity sandstone (Bentheim), a tight sandstone (Crab Orchard), and a microcracked granodiorite (Takidani). Laboratory data are then used with the permeability models of Guéguen and Dienes and Kozeny-Carman to investigate the characteristics that different void space geometries impart to measured permeabilities. Using the Kachanov effective medium theory, elastic wave velocities are inverted, permitting the recovery of crack density evolution with increasing effective pressure. The crack densities are then used as input to the microcrack permeability model of Guéguen and Dienes. The classic Kozeny-Carman approach of Walsh and Brace is also applied to the measured permeability data via a least squares fit in order to extract tortuosity data. We successfully predict the evolution of permeability with increasing effective pressure, as directly measured in experiments, and report the contrast between permeability changes observed in rock where microcracks or equant pores dominate the microstructure. Additionally, we show how these properties are affected by anisotropy of the rock types via the measured anisotropic fabrics in each rock. The combined experimental and modeling results illustrate the importance of understanding the details of how rock microstructure changes in response to an external stimulus in predicting the simultaneous evolution of different rock physical properties.Citation: Benson, P. M., P. G. Meredith, and A. Schubnel (2006), Role of void space geometry in permeability evolution in crustal rocks at elevated pressure,

Influence of relative humidity on fracture toughness of rock: Implications for subcritical crack growth

“…In order to better understand the fracturing in rock, it is therefore necessary to investigate the fracture toughness of rock. All rocks contain microcracks and microcavities (Sprunt and Brace, 1974;Nishiyama and Kusuda, 1994;Chen et al, 1999;Benson et al, 2006;Nara et al, 2011b). The influence of microcracks on the fracture toughness has been investigated by numerous workers, for example Nasseri and Mohanty (2008) and Nasseri et al (2005Nasseri et al ( , 2006Nasseri et al ( , 2007Nasseri et al ( , 2009Nasseri et al ( , 2011.…”

Pressure‐Dependent Elastic and Transport Properties of Porous and Permeable Rocks: Microstructural Control

“…Permeability is, however, not a physical property easily accessible in situ, and it needs to be attained through indirect means. To access it, several authors aimed at predicting permeability from correlation with other physical properties such as porosity (e.g., Brace, Walsh, & Frangos, ; Mavko, Mukerji, & Dvorkin, ), elastic wave velocities (e.g., Benson, Schubnel, et al, ; Benson, Meredith, et al, ), or electrical resistivity (e.g., Brace, ; Guéguen & Dienes, ; Milsch, Blöcher, & Engelmann, ; Revil & Cathles, ; Walsh & Brace, ).…”

Experimental Investigation of Wave Velocity-Permeability Model for Granite Subjected to Different Temperature Processing

“…Benson et al [26,27] change the porosity via loading. In this study, heat treatment is used to change the porosity.…”

“…Benson et al [26,27] modeled the permeability evolution of microcracked rocks with different void space geometries at elevated pressure and tried to establish the relationship of wave velocity and permeability. With reference to Benson's work, porosity is used as medium to establish a wave velocity-permeability model in this paper.…”