Understanding Zechstein Carbonate Reservoirs in NW Europe

Historically, Zechstein carbonate plays in NW Europe have had varying production success. Zechstein reservoirs account for some of the earliest hydrocarbon discoveries in the North Sea. Zechstein carbonates are also a current focus for exploration, for example in the area of the Mid North Sea High. Understanding the connectivity of the carbonates is critical in explaining the production history of fields and in applying these insights to future ventures.

To improve understanding of key factors affecting performance of Zechstein reservoirs we have carried out an extensive multi-disciplinary study involving integration and interpretation of new and legacy data from outcrops and sub-surface. World class Zechstein carbonate outcrops in NE England have been examined in conjunction with cored wells, published articles and production data (located in Fig. 1) to improve understanding of connectivity within Zechstein carbonates.

This study brings new insight into several factors that affect Zechstein carbonate reservoirs, including
• The characterisation of fractures, which have been extensively documented through lidar, photogrammetric and field measurements, and analysed within their structural, stratigraphic and diagenetic context to allow prediction of fracture behaviour within the reservoir;
• A revised basin-wide sequence stratigraphic framework, which allows application of the derived mechanical understanding in both the Northern and Southern Permian Basins.
The diagenetic effects in carbonate-evaporite systems, the processes and impact of brecciation associated with collapse following evaporite dissolution have also been studied. In addition, three fields which produce(d) from Zechstein reservoirs were studied to understand the production history in terms of connected volumes, water breakthrough, pressure support, and, in terms of applying the learnings from the other components of this study.

The findings have implications for both exploration and production. Play based exploration, testing of prospects and development of fields can all be informed from application of either, or both, of the resulting conceptual and numerical models.