New Prospects in Cambrian Platform Orthoquartzites in Poland?
LABECKI, J., Geological Bureau-Geonafta, Polish Oil and Gas Company, Warsaw, Poland, M. SCHLEICHER,* University of Clausthal, Institute of Geology, Clausthal-Zellerfeld, Germany, W. WEIL, Geological Bureau-Geonafta, Polish Oil and Gas Company, Warsaw, Poland, and H. KULKE, and J. KOSTER, University of Clausthal, Institute of Geology, Clausthal-Zellerfeld, Germany
Middle Cambrian orthoquartzites produce oil in two small fields northwest of Gdansk, Poland; few undeveloped offshore discoveries exist in the southeastern Baltic Sea. Our joint Polish-German study on these poorly porous sandstones is aimed at delineating areas of better reservoir quality development and thus of future prospects.
In the Polish part of the East European platform, Cambrian
deposits exist in four geologic provinces (Lublin slope, Podiassle depression, Warsaw synclinorium, Baltic syneclise).
In these areas, the Cambrian, which in part is more than 500 m thick, has been buried to depths between 300 and approximately 6000 m. The Middle Cambrian orthoquartzitic sandstones represent a shallow-marine sequence with interbedded claystones. Their porosities range from 2 to 8%, and oil production is improved by natural fractures. We hope to get a better understanding of control mechanisms of porosity-destruction processes by ongoing studies connecting sedimentology, regional petroleum geology, and diagenesis. Complex multiple quartz and carbonate cement generations are a prominent feature of these quartzites.
A major source rock for the oil accumulations is represented by Upper Cambrian black shales (TOC values, 3-13%; thickness approximately 1-10 m in northern onshore Baltic syneclise, up to 50 m in southern Scania, Sweden). The Middle Cambrian shales show low TOC contents (average, 0.3-0.6%) and a thickness of approximately 200 m. Despite their low organic content, they also could have contributed to the reservoired oil because both black shales show maturities within the oil window and both contain an oil-prone algal kerogen. Therefore, in this northeast Polish oil province the restricted pore volume of the orthoquartzites and not the source rock parameters represents the major limiting factor for larger oil accumulations.
Future prospects will be difficult to predict because the occurrence of traps might be much more controlled by diagenesis than by (tectonic) structures.
AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)