Ample evidence from petrographic and geochemical studies supports the hypothesis that fluid movement in sedimentary basins has a significant control on chemical diagenetic processes. Computer models allow reconstruction of basin paleohydrology and allow prediction of chemical reactions and mass transfer, but computational requirements of integrated models of chemical reaction-fluid flow normally result in one or other part of the calculations being overly simplistic. The proposed research involves integrating the results of separate paleohydrologic and chemical predictions to constrain diagenetic pathways in sedimentary basins. The approach is to use results from a completed study of the paleohydrologic evolution of the Gulf of Mexico basin to constrain temperatures, pressures, gas fugacities, and fluid:rock ratios in calculations of mineral-pore water interactions, which will be made using the EQ3/6 software package. Preliminary results show that predicted diagenetic sequences for Lower Tertiary Gulf of Mexico sandstones are in close agreement with sequences determined petrographically. Calculations of volumes of minerals precipitating and dissolving show that most modifications occur during early diagensis or immediately after a change in paleohydrologic regime. Proposed research will involve the further investigation of these preliminary results, including construction of hypothetical diagenetic pathways in several common hydrologic settings and will include a thermodynamic evaluation of the role of organic acids in enhancing mineral solubilities and the prediction of isotopic compositions of minerals and pore waters in each diagenetic pathway. Results from this research will improve our understanding of chemical diagenesis in sedimentary basins in general, and the Gulf of Mexico basin in particular, and will provide important guidelines for the development of combined chemical reaction- fluid flow computer algorithms and the interpretation of results from such calculations.
