Instabilities in geomaterials induced by dissolution

Abstract:

Deformation bands play an important role in reservoir engineering, geological storage, underwater landslides and slow geological procedures. Various mechanisms can be involved at different scales and may be responsible for deformation bands. Mechanical and chemical degradation of the grain skeleton is a softening factor that can lead to compaction, shear or even dilation band formation [1]–[3]. The present study is twofold. On one hand it focuses on the mathematical modeling of chemically induced strain localization instabilities in porous rocks and on the other hand it explores the conditions for their creation [4], [5].

In a saturated porous rock, the progressive mechanical damage of the solid skeleton during deformation, results in the increase of the interface area of the reactants and consequently in the acceleration of the dissolution rate of the solid phase [6]. Under the presence of dissolving fluids the solid skeleton is degraded more rapidly (mass removal because of dissolution), the overall mechanical properties of the system diminish (contraction of the elastic domain – chemical softening), deformations increase and the solid skeleton is further damaged (intergranular fractures, debonding, breakage of the porous network etc.). Based on a micromechanical model, the conditions for deformation band triggering are investigated analytically. The heterogeneity of the microstructure in terms of chemical reactivity of the constituents of the REV is taken into account resulting in a characteristic internal length of the system. The post bifurcation behavior is finally studied both analytically and numerically revealing the thickness of the localized zone.

References

[1] I. Stefanou and J. Sulem, DOI: 10.1002/2013JB010342

[2] M. Cha and J. C. Santamarina, DOI: 10.1680/geot.14P.115

[3] M. D. Ingraham, K. A. Issen, and D. J. Holcomb, DOI: 10.1007/s11440-013-0275-y

[4] K. A. Issen and J. W. Rudnicki, DOI: 10.1029/2000JB900185

[5] J. W. Rudnicki and J. R. Rice, DOI: 10.1016/0022-5096(75)90001-0

[6] L.-B. Hu and T. Hueckel, DOI: 10.1016/j.compgeo.2007.02.009

Figure: Profile of the vertical deformation at various times of a specimen under oedometric conditions. After a creep phase a compaction band evolves.