Zastosowanie modelu litologicznego dla uzasadnienia perspektyw gazonośności utworów czerwonego spągowca (saksonu) Polski

Abstract

THE USE OF LITHOLOGICAL MODEL IN VERIFICATION OF GAS POTENTIAL OF ROTLIEGENDES (SAXONIAN) ROCKS IN POLAND Summary In the last years, the Geonafta Enterprise was carrying out detailed lithological-facies studies on the Rotliegendes within the frame of cooperation with the Institute of Oil Mining in Moscow. The studies resulted in elaboration of a detailed lithological-stratigraphic scheme including subdivision of Rotliegendes section into petrographic complexes A, B, C, O, E1 and E2, based on average quantitative mineral composition. This made possible accurate correlation of Saxonian deposits. Three major areas of distribution of lithological-facies Saxonian complexes may be differentiated in Polish part of the Permian basin: southern (A), central (B) and northern (C). Typical Iithofacies relations found in each of these zones were used as model ones. I n constructing the model, there were identified five complexes of rocks (named as elements a, b, c, d and e). The complexes are characteristic of individual parts of a river pattern which originated due to prolonged action of a paleoriver, named as paleo-Oława river. The complexes-elements are characterized by both lithological regularities and specific development of gas traps. Facies analysis, carried out with the use of the lithological model of the paleo-Oława river suggested occurrence. of other, analogous river systems in southern part of the Permian basin and it made it possible to delineate zones most perspective for formation of deposit traps within these systems. Correlation of Saxonian rocks from northern, central and southern parts of the studied area gave further support to the hypothesis of two-phase development of Saxonian basin in two phases, differing in sedimentary conditions. The studies have shown the value of the lithological model for evaluation of gas potential of Saxonian rocks in poorly known but potentially gas-bearing areas in the Polish Lowlands. Gas-bearing structural traps from a belt of alluvial cones in forefield of mountain belt were found to be related to the zone of occurrence of paleowatersheds. This specific feature of the Permian basin in Poland should be taken into account in defining directions of further search. Further surveys of the recorded traps of the Iithological and structural types, especially those from slopes of paleoelevations, offer new possibilities in selecting trends in surveys aimed at discovery of new gas fields in Saxonian rocks.