Effects of oil charge on illite dates and stopping quartz cement: calibration of basin models

Oil can fill pores in reservoir sandstones at any burial depth by long or short distance migration. There has been a debate since 1920 concerning the effect of oil charge. We have made detailed local measurements of cements and porosity from individual fields and regional compilations from the North Sea. We consider that oil charge can be dated by K-Ar ages of fibrous illite, and oil stops quartz cementation in sands containing less than 20% water. Consequently, abnormally large porosity values can be preserved from 2 km down to more than 4 km of burial. Many oilfields are anomalously porous. K-AT dates within fibrous illite and quartz cement abundance can now be used to calibrate basin models back though geological time. (C) 2003 Elsevier Science B.V. All rights reserved.