Dynamics of Pressure Systems in the Netherlands North Sea

Verweij, Hanneke¹, Erik Simmelink¹, James Underschultz², Claus Otto² (1) Netherlands Institute of Applied Geoscience TNO - National Geological Survey, Utrecht, Netherlands (2) CSIRO Petroleum, Perth, Australia

The 3D characterization of present-day pressure distributions in the Netherlands part of the North Sea and their process-based understanding are subject of active study at TNO­NITG. These studies are carried out in research projects and – with CSIRO Petroleum – in joint-industry projects.

This paper focuses on the process-based understanding of the recently identified verti­cal and lateral pressure distributions in the inverted basins and adjacent highs in the North Sea area. Distinct pressure systems can be defined. On a large scale the Netherlands North Sea area can be subdivided in a normally pressured southern and a significantly overpres­sured northern region. Severely overpressured conditions occur in the regionally present Chalk Group, especially in the northernmost offshore, and in the syn-rift reservoir units of Late Jurassic -Early Cretaceous age, the Triassic early-rift units and Upper Rotliegend reser­voir units. The northern offshore region is significantly affected by Zechstein and Triassic salt deposits and structures; the reservoir units are, to a large degree, currently at maximum burial depth. In contrast, the southernmost offshore is not affected by salt deposits, was outside the main depocentre in Late Tertiary and Quaternary times and pre-Tertiary units are in large part not at their maximum burial depth. In general, the distinct hydrostratigraphic build-up and burial history of the two regions largely explain their characteristic pressure and fluid flow distribution.

The paper discusses the hydraulic characteristics of the subsurface and the main pres­sure influencing mechanisms in relation to the observed pressure distributions, using amongst other things, results from basin modelling (Petromod, Temis).