KINETICS AND MODELING OF FLUID-ROCK INTERACTIONS

The current state and most promising directions of kinetic investigati ons 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), deg ree of equilibrium, surface area, and activity of minerals. The sugges ted overall rate law includes all these parameters. There is a lack of kinetic data on reactions of incongruent mineral dissolution, which a re most typical for natural processes. Detailed observations show that kinetic features and reaction mechanisms are identical in natural env ironments 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 equat ions describing the rate of chemical reactions, fluid filtration throu gh the rock, and diffusion of components in the solution. These equati ons were used to ground the mathematical simulation of natural geochem ical systems and their time-space evolution. Reported are the estimate d time values required to approach the local chemical equilibrium at g iven conditions, and techniques for simple data scaling at varying con ditions. As shown, reactions at the boundaries between metasomatic zon es 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 testi ng the results of mathematical simulation, and in elucidating the summ ary kinetic effects of complex geochemical processes.