Barremian and Aptian Sediments in NW Germany - Plays for Unconventional Hydrocarbons?

Berner, Ulrich ¹; Heldt, Matthias ¹
(1) Petroleum and Coal Geochemistry, Fed. Inst. of Geosciences and Natural Resources, Hannover, Germany.

Lower Cretaceous sediments of the NW German Basin contain abundant organic material and are plays for unconventional hydrocarbons. We present a high-resolution study on Barremian and Aptian sediments, which aims at providing geochemical information for the assessment the hydrocarbon potential. It comprises inorganic as well as organic geochemistry to characterize the depositional environment, which influences the shale qualities of the Barremian and Aptian plays.

Barremian and Lower Aptian Paper Shales consist of organic-rich clay stones and marls of marine dysoxic to anoxic environments as obvious from high V/Ni- and low Al/TOC-ratios and high concentrations of sulphur and organic carbon (of up to 6.5 wt.-%) whereas the relative iron concentrations are comparatively low.

With the beginning of the Middle Aptian the amount of organic carbon decreases significantly to below 1 wt.-%. These clay stones and marls were deposited under oxic conditions as suggested by low V/Ni and high Al/TOC ratios. The interpretation is consistent with low sulphur, high iron and low carbon concentrations as well as with the information from other geochemical parameters.

Generally, all sediments contain mixtures of terrestrial and aquatic organic matter as indicated by pyrolysis and biomarker data. The preservation of the organic matter was good to excellent in the dysoxic to anoxic environments with more aquatic organic matter present but it was poor under oxic conditions. Although, the Middle Aptian sediments have no source potential, the Barremian and Lower Aptian Paper Shales as well as the Fish Shale may be regarded as potential source rocks. The overall thickness of these sediments is sufficient for a gas or oil shale target (>40m). However, the mix between land plant and aquatic material reduces the hydrocarbon potential slightly. The sediments may be oil to gas prone in the deep central and thermally mature parts of the NW German Basin where also higher thicknesses can be expected.

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