SPOIWA SKAŁ GÓRNEGO CZERWONEGO SPĄGOWCA W ZACHODNIEJ CZĘŚCI NIŻU POLSKIEGO W UJĘCIU KARTOGRAFICZNYM

Abstract

MAPPING OF CEMENT TYPES IN THE UPPER ROTLIEGEND ROCKS FROM THE WESTERN POLISH LOWLANDS

Abstract. Petrographic research was performed on Upper Rotliegend rocks from 76 boreholes. The contribution of individual components of cements and the sum of matrix was determined for sandstones and conglomerates to recognize their role in reservoir quality reduction. Allogenic pelitic-aleuritic components i.e. the matrix, and authigenic minerals i.e. the cements have been identified. The minimum and maximum contents of individual cement types were measured and their distribution is presented in maps. The matrix content in the deposits varies from 0.0 to 47.5% vol. The highest values were recorded in the Parzęczewo, Klęka and Siekierki environs of the Fore-Sudetic Monocline, and in the Bielica-Wysoka Kamieńska zone of Western Pomerania. Carbonate cements (0.0-49.6% vol.), represented by calcite and dolomite, and sulphate cements (0.0-29.5% vol.) are dominant in Western Pomerania. The highest content of quartz cement (20.7% vol.) is observed in Pomerania (Słowieńsko 1 borehole). In the Fore-Sudetic Monocline region, it rarely exceeds 10% vol. Carbonate, sulphate and quartz cementation resulted in considerable reduction of the rocks porosity, however commonly operating diagenetic dissolution allowed them to keep their filtration ability. Authigenic clay minerals are represented in the rocks of Western Pomerania largely by kaolinite and chlorite. Illite and mixed-layers illite/smectite (I/S) minerals occur in minor proportions. Diagenetic illite, accompanied by chlorites and I/S minerals, is commonly observed in the Fore-Sudetic Monocline. This illite, represented mostly by fibres forming meshwork microstructures in the pore space, was the strongest reducing factor of permeability, often destroying it completely.