Oil resources of the third Ciężkowice sandstone in the Osobnica oilfield (Silesian Unit, Polish Outer Carpathians) - sedimentological characteristic
Pawel Lis, Polish
Geological Institute, Regional & Oil Geology Department,
Described petroleum reservoir is the third Ciężkowice sandstone, composed of the late Paleocene age channel fill and depositional lobe succession. Osobnica field is a part of an ancient deepwater fan, referred to as the Eastern Fan. Within this horizon the seven sandstone packages interbedded with mudstone/fine sandstone deposits were recognized. The first three packages are characterized by a coarsening-upward and thickening-upward sequence, which are interpreted as depositional lobe sediments. The next four packages, roughly 40 m thick each, are characterized by a fining-upward and thinning-upward sequence, which are interpreted as channel fill deposits. Because of the large number of well data (156 well in the 1,6 km2 area) resources were calculated by volumetric method. For the purpose of geological modelling Landmarc co. ZMAPPlus software was used and the results were visualized with the ArcView program. In the Osobnica field the total resources are calculated on 491500 tons, from which some 352600 tons of oil have been exploited so fare. Map of the resources arrangement and the structural model allowed to point out the main factors controlling distribution of hydrocarbon resources in the Osobnica field. Among them the most important is the shape of the structural trap. The less important is a facies arrangement. The main part of oilfield is in the SE elevated part of the Osobnica anticline. Oil is accumulated in both channel- and lobe-type deposits. Among them, slightly more predestinated for hydrocarbon accumulating is the channel fill sandstone.