Changes in hydrologic properties of aquifer media due to chemical reactions: A review

Hydrologic properties that govern fluid flow through the subsurface are por osity, permeability, relative permeability, fluid-fluid and fluid-solid int erfacial areas, pore and particle size distributions, which may change due to dissolution/precipitation of minerals, fine particle release and capture , ion exchange, and clay swelling. Provided here is a review on the change of hydrologic properties in subsurface media due to chemical processes, and the modeling of such changes. Precipitation and dissolution processes affe cting the hydrologic properties, their kinetics and the effect of hydrodyna mic factors on such processes are discussed. Precipitation in carbonaceous, siliceous, alkaline and acidic environments, and the role of dissolution a nd clay swelling in formation damage are reviewed. Changes in properties of unsaturated and fractured media were also discussed. Traditionally, differ ent approaches were used to model various physico-chemical processes and th eir effect on the hydrologic properties. A detailed review of these methods , including the geochemical equilibrium and kinetic models, chemical divide pathway models, flow and transport models, precipitation/dissolution wave theory, network models, porosity and permeability reduction models, is pres ented. Recommendations are provided for the assessment of changes in the hy drologic properties of subsurface media attributable to chemical reactions, and modeling flow and transport in their presence. Further, research needs on the changes in hydrologic properties and constitutive relationships amo ng such properties in unsaturated media are identified.