DE JAGER, JAN, Nederlandse Aardolie Maatschappij, Assen, Netherlands, MARK DOYLE, Petroleum Development Oman, Muscat, Oman; PETER GRANTHAM, KSEPL/Shell Research, Rijswijk, Netherlands, and JOHN MABILLARD, Shell Nigeria, Port Harcourt, Nigeria

ABSTRACT: Hydrocarbon Habitat of the West Netherlands Basin

The complex West Netherlands Basin contains oil and gas in Triassic and Upper Jurassic to Cretaceous clastic reservoir sequences. The understanding has always been that the Carboniferous coal measures have generated only gas and the Jurassic marine Posidonia Shale only oil. However, detailed geochemical analyses show that both source rocks have generated oil and gas. Geochemical fingerprinting established a correlation of the hydrocarbons with the main source rocks. The occurrence of these different hydrocarbons is consistent with migration routes.

Map-based charge modeling shows that the main phase of hydrocarbon generation occurred prior to the Late Cretaceous inversion of the West Netherlands Basin. However, along the southwest flank of the basin and in lows between the inversion highs, significant charge continued during the Tertiary.

Biodegradation of oils in Jurassic and Cretaceous reservoirs occurred during the earliest Tertiary, but only in reservoirs that were at that time at temperatures of less then 70 to 80 degrees C, where bacteria could survive.

This study shows that also in a mature hydrocarbon province an integrated hydrocarbon habitat study with modern analyses and state-of-the-art technology can lead to a much improved understanding of the distribution of oil and gas in the subsurface. The results of this study will allow a better risk assessment for remaining prospects, and an improved prediction of the type of trapped hydrocarbons in terms of gas, oil, and biodegraded oil.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.