Coupled chemo-mechanics of evolving permeability in geomaterials

Flow of fluids in geomaterials may be strongly affected by chemo-mechanical processes, which are either externally induced or spontaneous. This is the case when dissolution, transport of the dissolved mineral and its precipitation in the neighborhood pore space causes a decrease of what is upscaled as Darcian permeability. Factors affecting the process are studied at the micro-scale using a model of a system of vessels of variable length and opening formed in the neighborhood of a stressed contact between two damage-affected grains. It appears that permeability is mildly affected by the contact area increase, and for most of the duration, by the precipitation of the mineral solute, until the inter-grain pores are almost completely clogged by the precipitate, when the permeability decreases very fast by orders of magnitude. Rigid chemo-plasticity model is employed to simulate the enhancement to dissolution induced by formation of new inter-phase interfaces at the walls of microcracks, represented by dilatant plastic strain. Such a process is widely believed to occur in oil/gas bearing sediments. Dissolution leads to chemo-plastic softening of the material. Couplings, feedbacks and feedforwards between mechanical, transport and geochemical processes caused by intergranular damage and dissolution are discussed.