The Jurassic as a Potential Source for a Thermogenic Contribution to Shallow Gas Accumulations in the German North Sea

Within the German Central Graben, the origin of shallow gas accumulations in Plio-Pleistocene sediments is still unknown. A contribution of thermogenic gas is assumed due to the occurrence of indicators on reflection seismic data for gas migration from a deeper source and the occurrence of thermogenic shallow gas within the Dutch Central Graben. The noticeable confinement of significant shallow gas accumulations to the Central Graben suggests a correlation to Jurassic formations that only exist in this area of the German North Sea. To assess the impact of potential Jurassic source rocks, six Jurassic formations were integrated into an existing petroleum model which was modified for the new purpose. Important Jurassic source rocks as the Posidonia Shale Formation or the Clay Deep Member were newly mapped for the German North Sea. Results from the petroleum model suggest Middle to Upper Jurassic coals and Lower Jurassic marine claystones as the most probable sources for a thermogenic contribution to the shallow gas accumulations.