Effect of pore-size controlled solubility on mineralization, porosity, andpermeability in porous media: a combined experimental and theoretical studyJay J. Ague and Simon EmmanuelDepartment of Geology and Geophysics, Yale University

Pore size is usually thought to influence the rate of crystal growth during diagenesis and metamorphism by controlling the ratio of surface area to fluid volume. However, theory suggests that in micron-scale to nanometer-scale pores, interfacial energy effects can also become important. We used mercury porosimetry to investigate the pore-size distributions in naturally cemented sandstone adjacent to stylolites and found that in highly cemented regions quartz precipitation was inhibited in pores smaller than 10 microns in diameter. Using numerical simulations of the mineralization process, we demonstrate that standard kinetic models cannot reproduce the observed pore-size patterns in mineralized samples; by contrast, excellent fits with the data are obtained when interfacial energy effects are taken into account (pore-size dependent model).

Moreover, as such micron-scale pores comprise the overwhelming majority of surface area in the sandstone, average reaction rates for the rock are significantly reduced. Reaction rates in geological media determined in field studies can be orders of magnitude lower than those measured in laboratory experiments, and we propose that reduced reaction rates in rocks with micron-scale porosity could account for the apparent paradox.