OZKAN, GONCA, and PETER ORTOLEVA
Laboratory for Computational Geodynamics, Indiana University, Bloomington, IN

Abstract: Role of Nucleation, Flow and Diffusion in the Development of Silica Cementation and Associated Seals

In silica rich systems, the texture dynamics and mineralization patterns are strongly coupled to fluid flow. As a result, the precipitation induced by fluid flow will change the texture and permeability, and thereby, will change the fluid flux, and hence precipitation. This dynamic can create mineralization zones with different seal/conduit properties. The patterns of: silica mineralization zoning is shown to arise out of the complex interplay between Ostwald ripening, Ostwald step-rule behavior and the reaction-transport dynamics of aqueous SiO₂ concentration.

In this study, the formation of silica layers and related seals. is analyzed with a quantitative model coupling silica diagenesis and pore fluid flow. The competitive heterogeneous nucleation and growth/dissolution of the SiO₂ polymorphs is simulated via the dynamics of the particle size distributions for the polymorphs and of the Si0₂(aq) concentration. A new algorithm is introduced that allows for the simulation of the full range of SiO₂ aggregates from monomer to centimeter-scale crystals. This diagenesis model is coupled to pore fluid flow to obtain the dynamics of the spatial variations of concentration, mineralogy and particle sizes. We apply the theory to determine the effect of initial sediment characteristics, thermal regime and fluid influx rate and composition on the formation of location and characteristics of silica cementation horizons.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas