Depth-Dependent Fault Sealing in the Greater Oseberg Area

We have re-examined the hydrocarbon distribution in the Greater Oseberg Area to get a more complete understanding of migration and trapping in the area. This work has included observations of oil vs gas, fluid pressure and fault sealing in the area, as well as re-examination of previous modelling work. We suggest that diagenetic fault sealing trapped hydrocarbons in several structures in the Greater Oseberg Area. The faults were largely open when the reservoirs were at shallow burial depths. Therefore, oil could migrate to the Oseberg Alpha structure from the north, and to the Omega structures from the west. The faults started to seal off as the rocks entered the temperature zone that is favourable for quartz diagenesis. This resulted in fault sealing at some places, and open fluid communication along faults (possibly below the fluid contact positions) at other places. Further burial resulted in complete sealing of the fault planes and therefore in pressure build-up. The diagenetic reactions progressed despite the high fluid pressures and resulted in pressures that reached the fracturing limit at Huldra. These high pressures resulted in leaked and underfilled segments here.