Pressures and Fluids
Published:January 01, 2011
Hydrodynamics-based approaches were used to characterise and analyse the present-day pressure and fluid-flow conditions in the Permian Rotliegend reservoirs in the Netherlands. These approaches involve the use of multi-well pressure– depth plots, regional all fluid overpressure maps, salinity maps, and hydraulic-head maps. The maps and plots revealed a general regional trend of, often stepwise, decreasing fluid overpressures from northeast towards the south. Values of fluid overpressure vary between hard geopressures (Pexcess > 40 MPa in block L2) and near-hydrostatic pressures (Pexcess < 1 MPa in southern offshore). The highest overpressures occur in a zone following the northern limit of the Permian Rotliegend reservoirs. The width of the zone of high overpressures extends southward into the onshore Netherlands in the area of the Lauwerszee Trough. The hydraulic-head map of the Rotliegend reservoir demonstrates the potential for a general southward dewatering direction.
The hydrodynamic evaluation identified that there are distinct regional differences between the southern and the northern part of the area with respect to important factors influencing both pressure generation (such as sedimentary loading and gas generation) and dissipation (by fluid flow) in the Rotliegend reservoir. The distribution of observed overpressures and hydraulic heads reflect these regional differences. We show that because the vertical and lateral dewatering of the Rotliegend reservoirs is controlled by the permeability framework, the regional variations therein exert a major influence on the observed distribution of fluid overpressure. Relatively high fluid overpressures are maintained in zones where dewatering of the Rotliegend is severely restricted. This is especially apparent in the southern part of the Dutch Central Graben and also in the northern part of the Lauwerszee Trough.
Figures & Tables
The Permian Rotliegend of the Netherlands
More than 50 years ago, the discovery of the giant Groningen Gas Field in the subsurface of the Netherlands by NAM B.V. marked a turning point inthe Dutch and European energy market initiating the replacement of coal by gas. Despite the fact that the Rotliegend dryland deposits in the Southern Permian Basin are one of Europe's most important georesources, no sedimentological overview is available to date for the subsurface of the Netherlands. This SEPM Special Publication presents for the first time such a summary of the present-day knowledge, including a comprehensive core atlas from on- and offshore wells.