Integrated Reservoir Connectivity Analysis, Zechstein Carbonate Reservoir, Northern German Basin

Corona, Francesco V.¹; Neble, Julie ¹; Rettenmaier, Karl A.¹
(1)ExxonMobil Production Deutschland GmbH, Hannover, Germany.

An integrated workflow is presented for evaluating static and dynamic connectivity of a complex Upper Permian Zechstein carbonate reservoir in the Scholen Production Concession of the Northern German Gas Basin. Sour gas production in the concession began in 1963 and involves drainage from multiple, tectonically emplaced and, in places, vertically stacked allochthonous Zechstein carbonate reservoir sections. These allochthons lie within the Permian Zechstein salt and overlie the in-place autochthonous Zechstein reservoir.

The key issues in the Scholen Concession are the static connectivity and fill-and-spill scenarios among the multiple Zechstein sour gas accumulations and the dynamic connection between the autochthonous and allochthonous reservoir sections. Understanding these issues is important in the evaluation of infill drilling opportunities and near-field appraisal wells.

An integrated reservoir connectivity analysis incorporating geoscience and reservoir engineering data (i.e., linking the fluids to the geology) revealed that the five main gas accumulations in the concession appear to be connected statically through a common aquifer and the in-place autochthon and most detached allochthons likely are connected dynamically with baffles. Some allochthons are isolated and contained high pressured reservoirs that are either gas or water bearing. Previous view of the Scholen Concession was that the five main accumulations were in separate, unconnected compartments and that most allochthons were not in dynamic pressure communication.

These learnings ultimately led to realistic and reliable evaluations of infill opportunities and near-field appraisals in the concession area, and changes to the drill-well inventory seriatim. Initial pressure and related resource capture were amended for infill well locations, and pressure depletion, drainage, and leakage risks were critically assessed for near-field appraisal wells. The potential of encountering isolated allochthons is still difficult to predict and, thus, is incorporated in the risking and uncertainty analysis of associated drill-well leads. In conclusion, this type of integrated reservoir connectivity analysis is essential in developing an understanding of the interrelationship of fluids and geology in the subsurface and can be applied not only in a production setting, but throughout the exploration, development, and production business cycle.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.