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

Abstract

Although several studies aimed at linking electrical and hydraulic transport properties in rocks, the existing models remain at most incomplete. Based on this observation, in addition to the transport properties, this contribution investigates the pressure dependence of P wave velocities and porosity for three porous rocks. Apart from hydraulic conductivity, all physical properties show an important dependence to the confining pressure. In particular, electrical resistivity reaches an asymptote at low confining pressures. Using the measured P wave velocities and effective medium theories, the microcrack density (ρ) and its evolution with confining pressure are estimated. For the three rocks, the microcrack density at which electrical resistivity reaches a plateau is of ρ ~0.13. This value corresponds to the threshold for crack percolation in media containing microcracks exclusively. This suggests that in porous and microcracked rocks, electrical resistivity is controlled by two independent hydraulic pathways of tubes and cracks acting in parallel. In contrast, this percolation threshold is not observed in the permeability data. A simple conceptual model is finally introduced that explains the fundamental differences between transport properties.

Volatile Degassing From Magma Chambers as a Control on Volcanic Eruptions

“…In practice, the concept of transient permeability introduces a theoretical challenge in modeling magmatic systems, since both the spatial and temporal scales at which permeability is being enhanced and subsequently reduced are small compared to those for magma reservoir evolution (millimeter‐centimeter scale vs. kilometer scale; days‐years compared to thousand years‐million years). Additionally, the permeability is a function of not only the porosity of the medium but also the pore geometry (size, connectivity, and crack shapes), alteration, multiphase fluid properties, temperature, and pressure (e.g., Burgisser et al, ; Colombier et al, ; Heap & Kennedy, ; Heap et al, , ; Kushnir et al, ; Parmigiani, et al ; Pimienta et al, ; Vasseur & Wadsworth, ). Consequently, variations in these properties lead to a multitude of mechanisms for both increase and decrease of transient permeability, some of which can be strongly nonlinear.…”

Variations in Elastic and Electrical Properties of Crustal Rocks With Varying Degree of Microfracturation

“…Further comparing formation factor‐to‐porosity (i.e., F ‐ϕ) variations with that reported in the literature (Figure b). Usual F ‐ϕ data sets aiming at the linking of the properties from varying one single parameter (e.g., pore size) investigate natural rocks that span porosities from 5% to about 30% (Lesmes & Friedman, ; Lesmes & Frye, ; Pimienta, Sarout, et al, ; Revil et al, , ; Titov et al, ; Tong et al, ; Weller et al, ). This new data set investigates specifically the effects of microcracks and evidences a change of slope in the F ‐ϕ trend for porosities below 5–7%, when compared to usual trends.…”

“…Permeability links directly to the rock porous network, in terms of its concentration and its connectivity (Bernabé, ; C. David et al, , ; Guéguen & Dienes, ; Pimienta, Sarout, et al, ; Sarout, ). Assuming simple geometries of either tubes (i.e., connected spherical pores) or penny‐shaped cracks, one could predict the permeability of a material.…”

Low pressure dependent elasticity of porous ceramics

“…Several theoretical studies have proposed empirical models to understand the temperature‐, pressure‐, and porosity‐dependent elasticity . To date, a number of experimental studies have reported the validation of the above theoretically proposed models …”

“…[12][13][14][15][16] To date, a number of experimental studies have reported the validation of the above theoretically proposed models. [17][18][19][20][21][22] However, there is a limited literature on experimental studies which characterize the influence of the pore-saturated fluid and its pressure on the elasticity of porous specimens. This work seeks to use resonant ultrasound spectroscopy (RUS) to experimentally illustrate the effects of saturated fluid properties on the elasticity of the porous material.…”