A Quality Controlled Pressure Database and a Regional Hydrodynamic and Overpressure Assessment in the Dutch North Sea

Erik Simmelink, Division of Geo-Energy, Netherlands Institute of Applied Geoscience TNO - National Geological Survey, PO Box 80015, 3508 TA Utrecht, Netherlands, phone: +31 30 2564623, erik.simmelink@tno.nl, Hanneke Verweij, Netherlands Institute of Applied Geoscience TNO - National Geological Survey, PO Box 80015, 3508 TA Utrecht, Netherlands, James Underschultz, CSIRO Petroleum, 26 Dick Perry Ave, Kensington/Perth, 6151, Australia, and Claus J. Otto, Petroleum, CSIRO, 26 Dick Perry Drive, Technology Park, Perth, 6151, Australia.

In a Joint Industry Project with four Dutch E&P operators, TNO and CSIRO Petroleum developed an extensive, quality controlled pressure and geological database of about 500 released wells from the Dutch part of the mud-dominated North Sea basin.

The process-based regional interpretation of the data, resulted in a subdivision of the subsurface of the Netherlands offshore into six hydrostratigraphic ‘domains'. Three overpressure regions could be distinguished, each with a characteristic hydrostratigraphy, burial history, overpressure magnitude and hydraulic head distribution. These regions are: 1) the severely overpressured northern offshore, where sealing shales, evaporites and salt structures cause stagnant conditions; 2) the normally pressured region in the south, where hydraulic head gradients are very small; and 3) a moderately overpressured region between these two regions, where relatively high, updip directed hydraulic gradients occur in several units. The lateral and vertical overpressure distribution and related hydrodynamic setting in the northern and intermediate regions are factors that influence present-day hydrocarbon migration and accumulation. Furthermore, the integrated analysis of pressure and salinity data showed specific sealing or conductive fault behaviour at various locations, which can be incorporated into future petroleum system assessments. The mapped salinity variations, with locally extreme saline conditions, are important for future estimates of formation water resistivity and could help in field development.

Overall, the project results have important implications for judgements pertaining to both hydrocarbon prospectivity and the reduction of drilling hazards.

Seals and Overpressure in Mud-Dominated Systems
2005 AAPG Annual Convention (June 19-22, 2005) Technical Program