Hydrodynamic Pressure Cell Systems in the Central Graben, North Sea

David Darby, Stuart Haszeldine, Cambell Fleming, Gary Couples

The sub-Cretaceous levels of the Central Graben can be divided into several pressure cells. These cells are in a state of geological disequilibrium; the basin will seek to re-equilibrate at hydrostatic pressure by releasing port fluids. We have identified cells in the Central Graben where flow is predominantly lateral. Other cells have restricted lateral flow due to structural position in the hydrodynamic flow system and fluid flow is predominantly vertical. We have identified pathways of potential pressure-driven flow towards a regional leak point located on an eroded intra-basinal high. Upward release of pore fluid from the leak point into the overlying normally-pressured regime is facilitated by the reduced thickness and elevated unit permeability of the pressure seal. The importance of this leak point has been identified through pressure cell definition and potentiometric mapping coupled to simulated regional overpressure evolution. Fluid flow from very deep overpressured cells into the high causes an important temperature anomaly over the leak point. Our model demon-rates a direct relationship between the position and characteristics of the pressure seal and the cell position in the hydrodynamic system.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995