CLAY DIAGENESIS IN RESERVOIRS - THE IMPOR TANCE AND EFFECTS ON POROSITY AND PERMEABILITY IN EXPLORATION-PRODUCTION

The main goal in inorganic geochemistry applied to oil exploration and production is to describe every fact participating in the poroperm ev olution oi reservoir formation during burial. Therefore, authigenic an d detrital minerals are studied, as well as reservoir waters. Followin g a relatively short period of mechanical compaction, porosity and per meability characteristics are influenced by cement crystallization and dissolution, and clay material growth. Porosity is dominantly affecte d by cement type behaviour, while permeability is controlled by the ch aracteristic Variations oi clays. In a classical diagenetic study, the first step is to constrain the temperature time evolution. Diagenetic steps are then reported to the burial curve, and consequences of each phenomena on petrophysical properties are estimated. Clay material is used to determine the absolute age of crystallization, partly to iden tify the characteristics of crystallization associated waters, and the refore to provide a background for the interpretation of the effects o f diagenesis in Exploration-Production. Theoretical considerations are in constant progress, and directly influence critical domaines of int erpretation (dating, modellization). So, close relations between inter preter and research groups are most recommended.