EPTING, MANFRED, JOHANNES WALZEBUCK, TOM REIJERS, MIEKE KOSTERS, RICHARD HUIS IN'T VELD, KOOS PIPPING, and MARK ORMEROD, Nederlandse Aardolie Maatschappij, Assen, Netherlands, and JOS OKKERMAN and JOACHIM AMTHOR, KSEPL/Shell Research, Rijswijk, Netherlands

ABSTRACT: Regional Trends in Reservoir Quality of the Rotliegende in the Dutch On- and Offshore

The vast majority of Dutch gas reserves are contained in Rotliegende sandstone reservoirs deposited as desert sediments in the southern Permian basin. Likewise, these reservoirs form the objective of some 60% of Nederlandse Aardolie Maatschappij's prospect portfolio. As the remaining prospects are often structurally more complex and buried to greater depth, diagenetic impairment and ensuing problems in productivity are becoming a major exploration risk. Therefore, a refined picture of the Rotliegende reservoir history was drawn in a multidisciplinary study. One of the main results is a clear relation between lithofacies association and reservoir quality, as demonstrated in large-scale cross sections from proximal to distal environments.

The key element controlling reservoir quality is the lithofacies association that reflects the textural maturity and the wetness of the sedimentary environment. A direct relation exists between the primary depositional environment and the early diagenetic phase during which most of the pore-plugging cements were formed. Sandstones deposited in a wet environment show the highest degree of cementation, while dry facies types retain more open pore space. Early diagenesis has a greater influence on porosity development than some later diagenetic processes (e.g., clay mineral growth) that may have occurred during thermal anomalies, fluid exchange, deeper paleoburial, and uplift.

In contrast to sections across the facies belts, correlations along depositional strike are more problematic due to intercalations of heterogeneous fluvial deposits and synsedimentary tectonics. In such cases, support of seismic interpretation and modeling is required to arrive at a meaningful prediction of prospectivity.

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