Dating Fluid Migration in the Tarbert Reservoirs of the Greater Alwyn Area (North Sea, UK) - Impact on Reservoir Quality

In the North Sea, areas with abnormal behavior and/or anomalously high reservoir quality preservation remain unexplained. The aim of this study is to understand processes responsible for the large variability in reservoir quality of the BRENT, observed in the Greater Alwyn Area. The tidal sandstones of the Tarbert Formation (Middle Jurassic) were investigated in two wells in the Forvie North and Jura condensate fields where it lies at depth of 3.5 km. Quantitative petrographic observations suggest that reservoir quality preservation is mainly controlled by retardation and/or inhibition of mechanical compaction due to less effective stress in Jura. P-V-T-X-t reconstruction of paleofluids migration history with modern fluid inclusions analytical procedure indicates earlier entrapment of hydrocarbon during the Eocene time (48 m.y.) in Jura, than in Forvie North (> 18 m.y.). The early hydrocarbon migration in Jura reservoir is associated with a significant fluid overpressure build-up that prevented the reservoir from extensive chemical compaction. In contrast, a later onset of hydrocarbon migration in Forvie North did not permit to inhibit efficiently mechanical and chemical compaction.