SZATAI, JOHN E., North Sea Oil Company Limited, Hamilton, Bermuda; and GREGORY A. SZATAI, Columbus Petroleum Co. Inc., Greenwich, CT

ABSTRACT: Overlooked Potential in the Rotliegend of the Eastern German North Sea: A New Exploration Frontier?

Success has eluded explorationists so far in the German North Sea. While over forty gas fields have been discovered during the past two decades on the south flank of the Permian Rotliegend basin onshore in Germany, some in the Wechselfolge, others in the basal main (Slochteren) sandstone but the majority in the Schneverdingen sandstones, in grabens located in a buried rift zone; no commercial accumulation has been found offshore in any Rotliegend formation.

The lack of success and resulting discouragement may be due to poor, or no, reservoirs in the Upper Rotliegend Wechselfolge; difficulties in reliable mapping of the basal main sandstone of the Upper Rotliegend and the resulting failure of locating adequate structures; and finally the apparent absence of Lower Rotliegend (Autunian) horst and graben structures with Schneverdingen type fill. High nitrogen content where gas was found was also discouraging.

Improvement in the acquisition and processing of new seismic data during the last four years made possible the reliable mapping of not only the basal-main sand but also the discovery and mapping of Lower Rotliegend strata and structures in the eastern North Sea.

Recent mapping there resulted in two significant findings:

1. The existence of a giant Northeast plunging structural high -- at least 90 km long and 25 km wide -- with the ubiquitous presence of an Upper Rotliegend Slochteren type basal main sand over the entire structure and numerous structural culminations at this horizon, representing drillable structures.

2. The discovery, for the first time in the German North Sea, of a buried rift zone underneath the basal main sand, of Lower Rotliegend (Autunian) age, over 50 km wide with numerous grabens and half half grabens which contain pre-rift, syn-rift, and post-rift sediments of considerable (up to 1,200 m) thickness. The grabens and half grabens are similar to the productive ones onshore to the southeast in Germany and the rift-zone that contains them may be the continuation of this onshore rift zone. Furthermore they may also contain Schneverdingen-type fill with fluviatile and eolian strata. Due to their juxtaposition to potential Carboniferous source rocks, accumulated gas in them could be of good commercial quality.

The giant Upper Rotliegend structure and the newly discovered buried Lower Rotliegend (Autunian) rift zone with its numerous grabens and half grabens have been overlooked. The first was barely tested, the second was untested, and they may represent a new exploration frontier in the eastern German North Sea.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.