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Keywords:

  • tectonics and sedimentation;
  • tight gas;
  • Rotliegend;
  • palaeo-topography;
  • isopach map analysis;
  • Southern Permian Basin

A combined tectonic-stratigraphic interpretation of three-dimensional seismic reflection, wireline log and core data is presented in this study focussing on a tight gas field in East Frisia, NW Germany. Upper Rotliegend reservoir rocks in the study area are of fluvio-aeolian origin and include dune, minor sandflat and wet to dry interdune deposits. Source rocks are Westphalian coals and a top seal is provided by Zechstein evaporites.

Detailed analyses of palaeo-topography, fault activity and accommodation space development for strata of Permian age (Rotliegend and Zechstein groups) indicate that local depocentres developed within small-scale fault-controlled transtensional sub-basins. Synsedimentary half-graben development and fault activity occurred during Upper Rotliegend II (mainly Elbe Subgroup) deposition. Many Upper Rotliegend structures were then reactivated during the Triassic, Jurassic and Cretaceous, often with enhanced offsets and increased lateral extent. As a consequence, Rotliegend structures and stratigraphy were significantly displaced resulting in the relocation of former Rotliegend depocentres and associated tight gas reservoir facies. This tectonic overprint hampers the prediction of potential Rotliegend reservoirs, and shows that palaeo-environmental restoration is required in areas which have undergone multi-phase deformation histories.

Exploration strategies in the study area have favoured drilling locations in present-day structural highs. This study suggests that sediment traps were controlled by synsedimentary Upper Rotliegend II to Zechstein palaeo-topography, defining a new concept for future tight gas exploration.