Petroleum System – Source Rock Draupne Formation Main Shale rock that forms the hydrocarbon source in this field Physical Characteristics Include Brownish Black Medium of Dark Olive Grey Non- Calcareous Mudstones Thickness of Formation typically 50- 250 m but may exceed 1200m in localized area Heather Formation Dark grey Silty Mudstones with thin Carbonate layers Thickness formation ranges up to 1000 m It is typically gas prone Total organic carbon ( TOC ) values are typically between 2-2.5 %

Petroleum System – Reservoir Rock Triassic and Lower Jurassic Occurs in tilted fault blocks with varying degree of Jurassic Cretaceous erosion and onlap. The main reservoir intervals comprise of thick , fluvial channel and sheetflood deposit. Porosity range from 20-24% Permeability 300-2000 mD Middle Jurassic Present in the Northen Sea are arkoses and subarkoses with quartz , clay minerals and Fledspars consisting about 95 % of the total miner Sandstones are both quartz and calcite cemented at depths exceeding 2500 m. Reservoir form a thick clastic wedge comprising laterally extensive interconnected fluvial Deltaic and coastal depositional systems with porosities 20-30% and permeability 50 – 500 mD.

Petroleum System – Traps and Seals Most trapping mechanism is provided by rotated faults sealed by fine grained post rift sediments. Seals These sediments draped on to the structures to form seals Lateral trapping and sealing is formed where reservoir rocks are juxtaposed with non-reservoir rocks at fault contacts Most seals are closed to hydraulic fracture.

Petroleum System – Migration Migration Mechanism Primary migration - Pressure driven flow of a discrete hydrocarbon phase through pores and micro fractures Secondary migration - Buoyancy resulting from difference in density between the hydrocarbon and water

2D Cross Section Imaging

2D Cross Section Imaging Anticline Hanging Wall Fault The structure shows a fault as indicated by the arrow and the existence of anticline, which makes it a suitable hydrocarbon reservoir trap. This 2D cross imaging will be compared to the static model that will be explained in the next section for accuracy comparison.

Stratigraphic Correlation Unconformity Thinning Strata S-N Thickening Strata S-N

Depositional Environment

Volumetric Estimation of Gullfaks Field

Breakdown Of STOIIP Based on Layers

Breakdown Of GIIP Based on Layers