Norbert Hoffmann¹

(1) Federal Institute for Geosciences and Natural Resources, Berlin - D 13593, Germany

ABSTRACT: New Indications for Pre-Westphalian Source Rocks in the North German Basin

Recent magnetotelluric measurements evidence the occurrence of good electrical conductors in the deep pre-Westphalian sediments of the North German basin. Petrophysical analyses prove that these layers can be correlated with TOC and pyrite-rich Alum (black) shale. For the first time, an attempt is being made to directly correlate magnetotelluric and organic-geochemical data for obtaining models of the distribution of these marine source rocks. As shown by the MT data, there is probably no regionally distributed pre-Westphalian source rock in the depocentre of the Rotliegend basin, and hence exploration for deep gas does not seem to be promising there. On the other hand, northeast of this area up to the southern Baltic, Cambro-Ordovician Alum shale, known from wells and outcrops in Scandinavia, may be correlated with good conductors at depths of 8 to 11 km. Although pyrolysis experiments indicate a gas formation potential for this source rock, no gas may be expected to be produced in situ because of the source rock's high maturity. The good conductors encountered south of the central basin at depths of 7 - 10 km correlate with the Dinantian and Early Namurian Alum shales identified in wells. Depending on the maturity of the organic substances, these rocks produce natural gas of various qualities along the Rotliegend fairway. Magnetotelluric data and their integrated modeling together with petrophysical and organo-geochemical data offer new possibilities for the interpretation of basin configurations and consequently new incentives for future hydrocarbon exploration.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado