Petrograficzno-petrofizyczna charakterystyka piaskowców eolicznych strefy Siekierki–Winna Góra (koło Poznania) w aspekcie poszukiwań złoż gazu zamkniętego w osadach czerwonego spągowca

Abstract

Petrographical-petrophysical characteristics of the Rotliegend eolian sandstones of the Siekierki–Winna Góra Zone (the Poznań region) in the aspect of search for gas trapped in deposits.A b s t r a c t . The studied Siekierki–Winna Góra region is situated in northern part of the Fore-Sudetic Monocline, close to its boundary with the Mogilno–Łódź synclinorium, and comprises areas stretching south-eastwards of Poznań. The top of the Rotliegend deposits occurs there at depths ranging from 3.5 to 3.7 km. The major aim of the studies was to establish petrophysical characteristics of Upper Rotliegend eolian sandstones these rocks and define influence of diagenetic processes (especially compaction and cementation) on their reservoir properties. The petrographical and petrophysical analyses covered mainly top parts of profiles of Upper Rotliegend eolian sandstones from 9 boreholes. On the basis of the detailed sedimentological and facies analyses, it became possible to distinguish three depositional eolian groups in the studied region. These groups are related to desert sedimentation environment, that is dune, interdune and redeposition environments. The studies showed reduction of porosity and permeability of Upper Rotliegend eolian sandstones in an area from Siekierki through Pławce, Miłosław and Komorze and further south-eastwards, despite of advantageous facies development of these rocks. Diagenetic compaction and cementation are the processes responsible for this reduction. However, reservoir properties of these sandstones appear sufficientto treat the above mentioned zones as prospective. Such depositional traps may be best treated as unconventional tight gasdeposits (Poprawa & Kiersnowski, 2008).