Importance of evolving fault seals on petroleum systems: Southern Halten terrace, Norwegian Sea

Abstract

The role of faults in petroleum systems is important especially in cases where the hydrocarbon accumulation in the prospect or field is fault-dependent. Usually, the properties of faults in petroleum systems are considered as static through time. We present a case study from the southern Halten terrace in the Norwegian Sea which highlights not only the importance of faults but also that the evolution of fault properties is key in determining the correct charge in the fields in the region. The best-fit model shows that in order to match observations the petroleum system requires at least two stages of hydrocarbon migration during which fault properties change from partially to completely sealing with respect to hydrocarbon flow across them. The most likely process that results in fault sealing is cementation due to increasing temperatures caused by the rapid burial during the Quaternary glaciations. This results in the most accurate charge of accumulations in the region while also explaining other observations such as present-day pressure compartmentalization and biodegradation. The best-fit model also implements the source rock thermal evolution based on a 2D basin model that improves the match of fluid GOR in the accumulation to the measured values. This study highlights the importance of multi-scale, multi-physics and multi-stage models in order to obtain results consistent with present day observations.