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X-ray micro computed tomography characterization of porosity in Rotliegend sandstones on the northern slope of the Wolsztyn Ridge, western Poland

Poszytek A., Mikołajewski Z., Dohnalik M.

Geological Quarterly

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2016

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Vol. 60, No. 4

801-810

EN

Natural gas in the Polish Rotliegend Basin occurs in porous and permeable aeolian sandstones, and traps are mostly structural. Lithological traps are rare and occur on the northern slope of the Wolsztyn Ridge where fluvial and aeolian sandstones overlap with alluvial facies. Both fluvial and aeolian sandstones are reservoir rocks in this area. The X-ray micro computed tomography (MCT) results and microscopic observations indicate that the sandstones in lithologic traps on the northern slope of the Wolsztyn Ridge form highly compartmentalized vertical reservoir rocks composed of four types of sandstones. The profiles are dominated by very low-porosity fluvial sandstones (F2), and low-porosity aeolian and fluvial sandstones (A2, F1). The A1 type of sandstones with high porosity (10%) occurs only in some sections of the profiles. The most important diagenetic processes that reduced porosity were compaction and cementation by carbonate cements. All studied sandstones were subjected to the same diagenetic processes. However, each of the processes ran with varying intensity in different types of sandstones. Detailed analyses of pore distribution by MCT methods with respect to primary depositional or lithofacies effects, and secondary diagenetic effects, help to understand the 3D geometry of pores and pore shape-size distributions. The results can be used in the studies of other sandstones with a different origin and age.

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The isolated Wuchiapingian (Zechstein) Wielichowo Reef and its sedimentary and diagenetic evolution, SW Poland

Fheed A., Świerczewska A. T., Krzyżak A.T.

Geological Quarterly

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2015

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Vol. 59, No. 4

762--780

EN

The development of a relatively small and isolated part of the Wuchiapingian, Zechstein Wielichowo Reef was possible owing to a progressive subsidence and frequent sea level fluctuations. Three biofacies were distinguished within the studied object: (1) a shallow-water and highly energetic Acanthocladia biofacies, dominated by bryozoans and crinoids, with poorly preserved porosity, reduced mainly by calcite cementation and compaction; (2) the Horridonia biofacies comprising numerous brachiopods, preferring a moderate depth of water, with comparably poor porosity; and (3) the Fenestella/Kingopora biofacies rich in fossils of the highest variability, related to the deepest and calmest waters, occurring on the top of the profile and showing a significant effective porosity, reaching almost 13%. Among many diagenetic processes altering the reef, several lines of evidence suggest that it was the meteoric diagenesis to enhance its porosity the most extensively. Since no stromatolites are present, the final sea level decrease is interpreted to be rapid, hence creating conditions favourable for the meteoric dissolution. Some intraparticle porosity, however, seems to be of a depositional origin.

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Interpretacja litofacjalna danych sejsmiki 3D kluczem do sukcesu w detekcji ciał rafowych w poziomie wapienia cechsztyńskiego w basenie permskim (na przykładzie rafy Kościan)

Górski M., Gierszewska D., Król E., Urbańska H., Wilk W.

Przegląd Geologiczny

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2000

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Vol. 48, nr 2

137-150

PL

Poziom wapienia cechsztyńskiego stał się jednym z najbardziej perspektywicznych poziomów zbiornikowych z punktu widzenia poszukiwań w Polsce. Rejon paleoelementu zwanego wałem wolsztyńskim był na początku transgresji morza cechsztyńskiego naturalnym miejscem sedymentacji typu rafowego na lokalnych paleopodniesieniach szelfu. Rafy te w wyniku gry naftowej stały się pułapkami akumułującymi gaz migrujący z utworów wieku karbońskiego. Dane sejsmiki 3D integrowane z pozostałymi rodzajami danych pozwalają na wydzielenie ciał rafowych-pułapek w procesie interaktywnej, komputerowej interpretacji opartej na czynniku litofacjalnym. Wykorzystuje ona informacje dostarczane przez geofizykę otworową i elementy paleogeografii możliwe do pozyskania z danych sejsmiki 3D. Wydzielenie pułapek umożliwia przejście do następnego etapu, polegającego na określeniu ich geometrii i porowatości. Pozwala to obliczyć zasoby złoża. Zastosowane procedury interpretacyjne zostały potwierdzone rezultatami 12 otworów odwierconych na rafie Kościan i czteroma następnymi na rafach Bonikowo, Białcz, Brońsko i Kokorzyn. Ich efektem jest osiągnięcie, niespotykanej w polskiej praktyce poszukiwań węglowodorów, skuteczności wierceń.

EN

The Zechstein LHmestone formation became one of the most perspective reservoirs as far as the to exploration carried out in Poland is concerned. The region ofpalaeoelement, referred to as the Wolsztyn ridge, used to be a natural sedimentation place of the reef type on the local palaeoelevation of the shelf at the beginning of the Zechstein sea transgression. As a result of hydrocarbon play, these reefs became accumulation traps for the migrating gas that takes it origin in the strata of the Carboniferous age. The 3D seismic data integrated with other types of data allow for the selection of reefs-traps in the process of interactive, computer analysis based on the lithofacies factor. It makes use of the information supplied by well logging and elements ofpalaeogeography which can be acquired from 3D seismic data. The selection of traps open the possibility of passing to the next stage which consists in determining geometry and porosity. The determination of the said allows to calculate reservoir reserves. The applied interpretation procedures have been confirmed by the results received in 12 wells in the Kościan reef and four others in the Bonikowo, Białcz, Brońsko and Kokorzyn reefs. The effect is the efficiency of drilling unprecedented so far in Polish practice of exploration.