Bidimensional Simulation of Oil and Gas Generation and Entrapment Across Northern Viking Graben (Norway), with Emphasis on Hydraulic Regime

J. Burrus, P. Ungerer, B. Doligez, P. Rabiller

A bidimensional forward numerical model was used to reconstruct the history of sedimentation, compaction, heat transfer, hydrocarbon generation, and migration along a 150-km southeast-northwest cross section in the Northern Viking graben.

The model is based on the heat equation and on the diphasic Darcy's law. An empirical relationship between porosity and effective stress was used to study the pressure regime. The model takes into account hydraulic fracturing and subsequent relaxation of pressures. A kinetic model describes the generation of hydrocarbon.

The study suggests the following.

1. The overpressures observed west of the Central graben in the Jurassic oil-rich reservoirs are well explained by the effect of burial and compaction if low permeabilities are introduced for the Cretaceous shales and for the faults that bound the tilted blocks. On the east, in contrast, the hydrostatic pressures that characterize the gas-rich pools are due to shallower burial.

2. Although rather impervious, the major faults allow fluid displacements at a geological time scale. A significant amount of oil is expelled from the Central graben to the western structures through and along the faults.

3. The high-pressure gradients found to the west have caused migration of the gas to cease, and only oil accumulation subsist. To the east, the low-pressure gradients are insufficient to displace the oil, and most accumulations consist of gas.

4. Hydraulic fracturing is a significant process for the expulsion of hydrocarbons from the overpressured source rocks as compaction and generation proceed.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.