Abstract: Primary Migration of Hydrocarbons from Sub-Zechstein Source Rocks of the Pomeranian Anticlinorium Area in the Light of Anomalous Compaction

GORECKI, W., M. STEFANIUK*, A. P. LAPINKIEWICZ, T. MACKOWSKI

Primary migration of hydrocarbons takes place as a pressure-controlled flux of hydrocarbon phases from silty-clayey source rocks to reservoir rocks. The necessary condition for initiating the process is a sufficient saturation of source rocks' porous space with hydrocarbons. When a threshold saturation is not exceeded, the expulsion of water solution and the mixture of hydrocarbons due to compaction become important.

An analysis of the compaction and fluid expulsion rate for silty-clayey lithotype of Sub-Zechstein complexes was made for five boreholes of the Pomeranian area. Compaction curves were evaluated with neutron-gamma logs. Curves of mean abnormal compaction and an expulsion rate were taken into account. Assuming mean compaction curves, 80-90 per cent fluid volume was removed from source rocks before they reached the hydrocarbon generation window. Thus the expulsion due to compaction could not be of importance. Considering the abnormal compaction process due to anomalous porosities of Devonian, Carboniferous and Permian source rocks, the generation window was achieved with a significant amount of fluid in intergranular space. Hence, the compaction mechanism of primary migration could be essential.

A spatial analysis of fluid content distribution in source rocks and of generation window distribution was made at selected intervals of geological time.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria