Coupled chemo-mechanics: A comprehensive process modelling for energy Geotechnics
Geo-chemistry and geo-mechanics have had a fruitful period of independent development over last 50 years, and are now conceptually matured having produced useful and sophisticated modeling tools used in the energy industry. As the understanding of the processes becomes more in-depth, interdependence of chemical and mechanical phenomena in geo-materials are more and more appreciated. The primary variables/properties that are involved in the interdependence are mineral, ion and proton mass transfer between porous medium phases and mechanical stiffness and deformation, and soil permeability. The paper outlines the efforts in modeling of coupling of geochemical reaction laws and laws of deformation and fluid flow. It identifies changes of mass of ion concentration, electrical charge, or individual solid minerals as primary chemical variables affecting the constitutive mechanical laws of behavior of rocks and soils, aswell as of the fluid or species transport in the porous media. Examples of chemo-plasticity and chemo-elasticity are discussed. A particular case of chemical softening or hardening as a function of mineral mass removed or added is focused on. Additional chemo-mechanical coupling comes via micro-fracturation, which generates an extra specific surface area of fluid/solid interface, at which an enhanced dissolution, and/or precipitation takes place. Formulations of permeability evolution due to chemo-plastic process are also reviewed. Experimental data and simulation results are discussed for processes exemplified by reservoir sediment aging/pressure solution and compaction, acidization enhanced subcritical crack propagation in hydraulic fracturing, or due to CO2 injection. Importance of multi-scale considerations (both for time and space scales), as well as of innovation in chemo-mechanical experimentation are emphasized.
