The hydrodynamics of the Snorre Field area, offshore Norway

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Abstract
The Snorre Field, in the Norwegian North Sea, contains a 300 m oil column and is characterized by high pressures. The Snorre Field and its satellites are a well‐documented area and it was considered as an excellent case history for documenting hydrocarbon migration and petroleum hydrodynamics in an overpressured regime. The reservoirs are Triassic and Lower Jurassic sandstones overlain by thick shale formations. The overpressure in the acquifer is 14 MPa. The variations of the oil‐water contact levels observed throughout the structure can be correlated with oil density variations. This implies that some faults are partly sealing and suggests that leakage through the cap rock is possible together with a selective input of hydrocarbons within the compartments. The possible mechanisms of pressuring and their consequences on the migration system are discussed in this paper.The origin of abnormal pressures in the reservoir is not directly related to the vertical overburden. Some equivalent overpressures due to the compaction exist further south at the North Alwyn location. An equalization of about 14 MPa overpressure occurs along a SW‐NE structural trend, through the North Alwyn, Brent, Statfjord and Snorre fields. Snorre being at the shallowest depth, the pore pressure at the top of the reservoir reaches the stress limit for fracturing and hydrocarbons leak from the field.The idea that a large structural trend acts as a preferential route for the migration of hydrocarbons is well supported; however, the oils in Snorre have a GOR increasing from the southwest to the northeast part of the field and this feature, supported by organic geochemistry, reflects an input of light hydrocarbons from source areas in the adjacent 34/5 basin to the east where high pressures are generated. Evidence for high pressures in the basin exists on seismic profiles, where velocity anomalies indicate highly pressured deep zones and migration possibilities along fractures or unconformities.The pressure regime and the stress conditions are key points for the exploration in this area, together with the sealing capacity of the main faults.