Modeling Clastic Diagenetic Systems during Progressive Burial

Abstract

The volumetrically important diagenetic reactions that result in significant porosity and permeability enhancement include framework grain and carbonate cement dissolution. The distribution in space and time of many of these reactions is mediated by organic/inorganic interactions. These interactions can be modeled by using coupled pathway, kinetic, and water-rock equilibria models. Pathway models suggest which diagenetic reactions are likely to occur, and how pore water chemistry will change with progressive diagenesis. Kinetic models predict the position in space and time of kinetically driven reactions; they require detailed knowledge of the time-temperature history of the system and the reaction kinetics involved. Water-rock equilibria models predict the thermodynamic direction of diagenetic reactions; for basin modeling, knowledge of the thermodynamic properties for reactions of interest as well as the time-temperature history of the system is required. These data are available for a variety of geochemical reactions of interest in many sedimentary basins. Preliminary results demonstrate that these techniques neatly predict porosity/permeability distributions in sand/shale sequences in some basins. The techniques appear to work best in basins where source and reservoir rocks are intercalated (minimizing fluid migration distances), as well as basins characterized by sporadic hydrodynamic events (e.g. seismic pumping and/or pressure chamber rupture).