Chemically induced compaction bands: Triggering conditions and band thickness

Abstract

During compaction band formation, various mechanisms can be involved at different scales.Mechanical and chemical degradation of the solid skeleton and grain damage are important factors that may trigger instabilities in the form of compaction bands. Here we explore the conditions of compaction band formation in quartz-and carbonate-based geomaterials by considering the effect of chemical dissolution and grain breakage. As the stresses/deformations evolve, the grains of the material break, leading to an increase of their specific surface. Consequently, their dissolution is accelerated and chemical softening is triggered. By accounting for (a) the mass diffusion of the system, (b) a macroscopic failure criterion with dissolution softening, and (c) the reaction kinetics at the microlevel, a model is proposed and the conditions for compaction instabilities are investigated. Distinguishing the microscale (grain level) from the macrolevel (representative elementary volume) and considering the heterogeneous microstructure of the representative elementary volume, it is possible to discuss the thickness and periodicity of compaction bands. Two case studies are investigated. The first one concerns a sandstone rock reservoir which is water flooded and the second one a carbonate rock in which CO 2 is injected for storage. It is shown that compaction band instabilities are possible in both cases.

Dissolution of randomly distributed soluble grains: post-dissolution k0-loading and shear

“…1,1 m 2 /g to a sediment with e ¼ 2,7 and S S ¼ 50,200 m 2 /g (Herrera et al, 2007). Fluid permeability changes (Zheng & Elsworth, 2012) and chemically induced compaction bands have been attributed to dissolution coupled with grain breakage (Stefanou & Sulem, 2014).…”

Dynamical effects during compaction band formation affecting their spatial periodicity

“…In fact, field evidence related to compaction localization generally shows that CBs typically form in lightly cemented or uncemented sandy materials, subjected to a vertical overburden ranging from a few MPa to 30 MPa and to pore pressures of less than 13 MPa, at undisturbed (initial) porosities of n 0 = 10-25% [Holcomb et al, 2007], and permeability κ between 2 and 20 darcies (i.e., saturated hydraulic conductivities in the Fossen et al, 2011]. CBs' thicknesses are typically less than 1.5 cm [Holcomb et al, 2007;Stefanou and Sulem, 2014] and the CB formation can bring about in highly porous materials a porosity reduction of 10% to 20% [Olsson, 2001;Klein et al, 2001;Holcomb et al, 2007], corresponding to a volumetric deformation larger than 10%, relative to the surrounding uncompacted material.…”

“…This aspect was recently brought to attention by Regenauer-Lieb et al [2013], who proposed a rate-dependent model where the hydromechanical properties of the material and the velocity of deformation can be correlated with the periodicity of CBs. Further, Stefanou and Sulem [2014] discussed the thickness/periodicity of CBs in relation to material properties like grain crushability and hydraulic diffusivity. Chemenda [2009] showed, resorting to bifurcation analysis of compaction banding, that the ratio between CB thickness and spacing is related to all stress-strain parameters, with special reference to the hardening modulus.…”

Dehydration‐induced instabilities at intermediate depths in subduction zones

“…Here we model coupled dehydration and deformation in antigorite using, as a first approximation, a time‐independent inelastic flow law which includes strain hardening, strain‐dependent dilatancy/compaction, and a porosity‐dependent yield envelope. Our approach is based on the concepts typically used to model the behavior of porous rocks [e.g., Rudnicki and Rice , ; Issen and Rudnicki , ; Wong and Baud , ; Stefanou and Sulem , ], and dehydration has here an indirect effect by contributing to the overall change in porosity and fluid pressure. In this framework, two types of instabilities can arise: a rate‐independent bifurcation related to the constitutive behavior of the rock and a reaction‐driven, rate‐dependent instability (in the Lyapunov sense) due to the growth to small pore pressure perturbations.…”