Kinetics and modeling of fluid-rock interactions

The current state and most promising directions of kinetic investigations are discussed. The results of theoretical and experimental studies on reactions of congruent mineral dissolution were used to show some characteristics of reaction mechanisms and to elucidate the dependence of reaction rates on such kinetic parameters as the temperature, pH, concentrations of dissolved components (catalysts and inhibitors), degree of equilibrium, surface area, and activity of minerals. The suggested overall rate law includes all these parameters. There is a lack of kinetic data on reactions of incongruent mineral dissolution, which are most typical for natural processes. Detailed observations show that kinetic features and reaction mechanisms are identical in natural environments and experiments, however the reaction rates measured in the field are usually lower than the laboratory results. Possible factors responsible for this distinction are considered along with basic equations describing the rate of chemical reactions, fluid filtration through the rock, and diffusion of components in the solution. These equations were used to ground the mathematical simulation of natural geochemical systems and their time-space evolution. Reported are the estimated time values required to approach the local chemical equilibrium at given conditions, and techniques for simple data scaling at varying conditions. As shown, reactions at the boundaries between metasomatic zones and in the thermogradient systems may deviate from the equilibrium state throughout the entire period of fluid filtration. The considered examples of experimental modeling illustrate its efficiency for testing the results of mathematical simulation, and in elucidating the summary kinetic effects of complex geochemical processes.