Remarks on the solid and bulk responses of fluid-filled porous rock

Abstract

The volumetric response of fluid-saturated and linearly elastic rock due to a change of either mean stress or pore pressure is characterized by three independent material parameters. The unjacketed bulk modulus is a convenient choice because it can be directly measured in a laboratory test under a loading that preserves the difference between the mean stress and the pore pressure constant. For a monomineralic rock, the measurement of the unjacketed bulk modulus is ignored because it is assumed to be equal to the bulk modulus of the solid phase. To examine this assumption, we tested porous sandstones and limestones mainly composed of quartz and calcite, respectively, under the unjacketed condition. Special attention was dedicated to reaching full saturation ensuring the transmission of the pore pressure to the solid frame. The presence of microscale inhomogeneities, in the form of nonconnected (occluded) pores, was shown to cause a considerable difference between the unjacketed bulk modulus and the bulk modulus of the solid phase. Furthermore, we found the unjacketed bulk modulus to be independent of the unjacketed pressure and Terzaghi effective pressure and therefore a constant.

Changes in rock matrix compressibility during deep CO2 storage

“…Its permeability is ∼10 −14 m 2 . 10 Indiana limestone is also known as a freestone, which indicates that no preferential splitting direction exists, providing an advantage in utilizing the material for buildings and public structures. 54 Quartz and calcite are selected for this study as the major minerals forming the considered two types of reservoir rock.…”

“…For porous rock, the compressibility of its matrix is peculiarly important, since it solely provides an understanding of the volume response of the rock frame. 10 This pressure-independent material property can be measured under the unjacketed boundary condition, where the change in the total mean stress P is equal to the change in the pore pressure p f ( P = p f ). 11 With the measurements of the volume response, the unjacketed bulk modulus K s ' can be defined as:…”

“…13 However, the bulk moduli of the solid and the matrix can differ under conditions where the material is microscopically inhomogeneous (e.g., consisting of several minerals with different compressibilities) or contains nonconnected or occluded pores. 10 Additionally, while it was sometimes reported that the unjacketed bulk modulus could be a function of applied stress, [14][15][16] it is generally accepted that if the tested rock is fully saturated and the appropriate diffusion times for pore fluid pressure are considered, K s ' should not depend on the total and effective mean stress. 10,[17][18][19] Besides the poroelastic response, a chemical interaction between the rock, brine, and CO 2 may occur, which has long been generating a considerable interest for researchers related to its effect on the hydromechanical behavior of geomaterials.…”

“…10 Additionally, while it was sometimes reported that the unjacketed bulk modulus could be a function of applied stress, [14][15][16] it is generally accepted that if the tested rock is fully saturated and the appropriate diffusion times for pore fluid pressure are considered, K s ' should not depend on the total and effective mean stress. 10,[17][18][19] Besides the poroelastic response, a chemical interaction between the rock, brine, and CO 2 may occur, which has long been generating a considerable interest for researchers related to its effect on the hydromechanical behavior of geomaterials. The geological formations targeted for GCS are usually deep saline aquifers with capacities of thousands of megatons that are mostly composed of silica-rich (sandstone) or calcite-rich (dolomite and limestone) rock.…”

Evolution of poroviscoelastic properties of silica-rich rock after CO2 injection

“…Dry Poisson's ratio is measured in the uniaxial compression test [18] and the undrained Poisson's ratio νu is calculated from Equation (9). Here, the unjacketed bulk modulus is taken as Ks' =30 GPa [24].…”