Geochemical modelling of sandstone diagenesis and its consequences on the evolution of porosity

Abstract

Geochemical modelling of fluid-rock interaction is one theoretical approach that can be used for understanding diagenetic processes and their effects on reservoir quality. Results of successive modelling of dissolution and heating, using two specific path calculation codes DISSOL and THERMAL, from 25 to 160°C, are presented. If one considers one volume of reacting solution, the diagenetic effects are very important for fluid chemistry, while mass transfers have little effect on porosity. Only cumulative effects due to the circulation of fluids in reservoirs may explain the extent of diagenetic processes on minerals. Comparison between the computed data (this study) and available data from the North Sea, from Gulf Coast sandstones, from Pattani Basin (Gulf of Thailand), from San Joaquin Basin (California, U.S.A.) and from a Triassic sandstone reservoir in the Rhine Graben (Cronenbourg, France) show interesting similarities in the chemical evolution of the fluid. The modelling has interesting implications for the relations between ph- pCO 2 conditions and the diagenetic stability of calcic plagioclase.