Reservoir properties of the Palaeozoic-Mesozoic sedimentary cover in the Kraków-Lubaczów area (SE Poland)

Abstract

During the 50-year-long intense petroleum exploration of the Palaeozoic–Mesozoic basement of the Carpathian Foredeep, more than 20 oil and gas accumulations have been discovered. The basic and most important oil-bearing levels in the Mesozoic section are Oxfordian carbonates and Cenomanian sandstones. The Nosówka, Zalesie, Trzebownisko–Krasne, Cetynia, Uszkowce and Lachowice hydrocarbon accumulations and numerous hydrocarbon shows have been found in the Palaeozoic horizons. This paper is focused on evaluation of reservoir properties of the entire Palaeozoic–Mesozoic basement of the Carpathian Foredeep and marginal part of the Outer Carpathians for finding new reservoir horizons. 558 rock samples from 51 wells in the Kraków–Lubaczów area were analysed. The well log results from 20 wells were additionally used for the assessment of petrophysical properties. The results of porosimetry measurements and well logs varied in all discussed Palaeozoic and Meso- zoic basement horizons of the Carpathian Foredeep. The best reservoir properties were estimated within the Jurassic–Lower Cretaceous carbonate complex. Despite great variability, the carbonate rocks display highest average porosity and good permeability values. The variability of reservoir properties is mostly a result of the character of the reservoir-porous-fracture space. Good reservoir properties were also estimated for the Upper Cretaceous carbonate rocks. However, in most of the analysed wells the potential reservoirs were watered. The Palaeozoic complex displays weaker reservoir properties and they mainly refer only to the Devonian–Lower Carboniferous horizon. The Lower Palaeozoic rocks display weak reservoir properties. Their potential is additio- nally lowered by negligible range of occurrence and a small thickness. Generally, the gas- and oil-bearing pro- perties of the analysed zone can be attributed only to the Jurassic–Cretaceous reservoir horizons. The remaining horizons, especially the Upper Palaeozoic complex, are only supplement to the reservoir potential of the area.