Geochemical modelling of late diagenetic processes in the Brent Sandstone, Alwyn South area (East Shetland Basin, North Sea): 1. Estimation of the circulated fluids composition

Abstract This study simulates the third diagenetic stage of the Brent Sandstone in the Alwyn South area through modelling of water-rock interactions at temperatures of 120° and 140°C, as determined by the fluid inclusion method. Simulation results are compared to those from petrographic analyses. The major diagenetic events are recognized petrographically, but data on the chemical speciations of the invading fluid are not available. Thus, the geochemical simulations test both seawater and dilute water. A solid solution model is used in order to test the precipitated complex clay phase and its influence on the chemical composition of the reacting fluid. The best agreement with petrographic analyses is from rock interaction with seawater that is depleted in magnesium.