Geological factors effecting compartmentalization of Rotliegend gas fields in the Netherlands

Since the discovery of the Groningen field, fifty years ago, more than 250 gas fields have been discovered in the Netherlands. A study of most of these fields shows that connected volumes are often smaller than expected from volumetric evaluation. Seismic uncertainty can often be argued as an explanation for the discrepancy, but there may be also a geological explanation. Most gas fields are found in the Permian Rotliegend and good drainage is expected because the reservoirs are relatively thick and homogeneous. Minor faulting is often thought to cause drainage problems, but this study shows it is likely in a number of cases. Twenty three Rotliegend fields with connectivity problems have been studied in part of the Dutch offshore. This analysis outlines a number of regions in the Rotliegend fairway that share a risk for fault seal and therefore reduced connected volumes. Fault seal analysis is important to understand compartmentalization but does not explain all discrepancies. In a number of regions, fault seal analysis is unsuccessful because cataclastic sand-to-sand sealing strike–slip faults are difficult to detect. Stratigraphic compartmentalization is seen to play a role in some well defined areas of the basin. A better understanding of the connectivity problems can highlight areas attractive for appraisal and near field exploration.