POROSITY PREDICTION IN QUARTZOSE SANDSTONES AS A FUNCTION OF TIME, TEMPERATURE, DEPTH, STYLOLITE FREQUENCY, AND HYDROCARBON SATURATION

The variation of porosity in quartzose sandstones is calculated as a f unction of depth, temperature gradient, burial rate, stylolite frequen cy and hydrocarbon saturation. Calculations were performed by consider ing the effects of both mechanical compaction and chemical compaction/ cementation. This latter process dominates at temperatures greater tha n approximately 90 degrees C and is due to quartz redistribution withi n the sandstone. Quartz redistribution stems from clay-induced quartz dissolution at stylolite interfaces, coupled with diffusional transpor t of aqueous silica into the interstylolite sandstone and precipitatio n on quartz surfaces as cement. Many model parameters are obtained fro m theoretical calculations or laboratory measurements, and few basin-d ependent parameters are required to make porosity predictions. A set o f porosity predictions is presented in porosity/depth figures. Close c orrespondence between computed results and measured porosities in core s from a variety of sedimentary basins demonstrates the accuracy of th e predictions.