Aspects of 3D basin modeling of the Dutch Central Graben area

J.M. van Buggenum¹, F.F.N. van Hulten², and P.W. Gibson^3
1Wintershall Noordzee B.V. – P.O. Box 1011, 2280 KA – Rijswijk, The Netherlands
²Energie Beheer Nederland B.V. - P.O. Box 6500, 6401JH - Heerlen, The Netherlands
³Total E and P Nederland B.V. – P.O. Box 93280, 2509AG – The Hague, The Netherlands

Over the last 40 years exploration in the Dutch sector of the North Sea, in particular for gas, has been very successful. New discoveries are still being made, however, the number of exploration wells in the country is declining. Now is the time to look outside the conventional play areas and to seek new horizons. The Dutch Central Graben, positioned in the northern part of the Dutch continental shelf, is an intriguing geological province where, after the initial phase of exploration in the 1970s and 1980s not much drilling has taken place. Compared to the UK and Norway, the more than 100 km long southern extension of the North Sea rift system in the Netherlands is under explored. It has yielded only modest successes despite containing a number of proven reservoirs and source rocks and having a good seismic coverage. To better identify prospective areas for exploration a proprietary basin-wide modeling study, based on detailed structural mapping and all released wells, was undertaken by Wintershall, Total, Fugro Robertson Ltd and EBN. The aim of the study was to model the burial and maturation, and to predict the timing of hydrocarbon generation, of potential source rocks.

An extensive geochemical and geothermal database was built using data from more than 100 wells in the area. This data was used to characterize the source rocks and constrain the model. The burial history of the area was modeled using a 3D structural model built from detailed interpretation of the available 2D and 3D seismic data, calibrated with well data. The study area covered nearly 10,000 km²and included most Dutch offshore Quadrants F, G and the upper parts of Quadrants L and M. Construction of this model posed a number of problems and was perhaps the most challenging aspect of the study. Among the challenges were issues such as the thickness of the section eroded at the major unconformities, how to model lateral and vertical salt flow and how to populate the structural skeleton built from the seismic data with the fine detail seen in the wells. This stratigraphic interpolation was, for example, severely complicated by the incomplete sections of post Zechstein formations in many wells because of salt movements. Despite these problems the 3D geological model turned out to be a very valuable tool to understand the complex history of rifting, halokinesis and structural inversion of the different subbasins. The model gave a good understanding of the extent and boundaries of the basins and the platform areas. It can explain observed different heat flows in the areas.

The 28 grids from the 3D geological model, together with the parameters derived from the geochemical database were then transferred to a 3D (IES petroMod) modeling program. Despite the considerable size and complexity of the project a quality check of hand contoured maps based on 31 wells and 35 synthetic in a 1-D model versus the machine generated maturity maps showed that the 3D machine generated maps were stable and not significantly different.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands