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Comparison of joint sets orientation in the Lower Paleozoic shales exposed in Scania (SW Sweden) and concealed in N Poland : a multi-methodological approach

Olkowicz Marcin, Bobek Kinga, Jarosiński Marek, Pachytel Radomir

Geological Quarterly

2021

Vol. 65, No. 4

s. 258--275

The Lower Paleozoic shales of SW Sweden and Eastern Pomerania (Poland) have a common history related to the depositional and tectonic evolution of the Baltic Basin. The major tectonic events are recorded, among others, as joints, which are either exposed in outcrops in SW Sweden or recognised in deep boreholes located in Pomerania. We present a comparison of the regional joint systems recognized by multiple methods in the studied region. In effect of a statistical compilation of measurements, five joint sets (named JS 1 to JS 5) were identified, traceable between Eastern Pomerania and SW Sweden. Our analysis showed a general consistency of joint set orientations, independent of their distance to the Tornquist tectonic zone passing through the study region. Three of the joint sets, JS 1 striking NNE, JS 2 striking WNW, and JS 3 striking NNW, are found to be the most frequent sets, occurring in most sites. Having more constant orientation, the JS 1 and JS 3 served as indicators of possible rotation of the tectonic block or stress field in the region. JS 1 and JS 2 are interpreted as an effect of late Carboniferous stress relaxation after Variscan collision, while JS 3 and the E–W striking JS 4 might be related to the Early Devonian Caledonian compressive stage.

Prospective zones of unconventional hydrocarbon reservoirs in the Cambrian, Ordovician and Silurian shale formations of the East European Craton marginal zone in Poland

Podhalańska Teresa, Feldman-Olszewska Anna, Roszkowska-Remin Joanna, Janas Marcin, Pachytel Radomir, Głuszyński Andrzej, Roman Michał

Geological Quarterly

2020

Vol. 64, No. 2

342--376

The paper presents the latest state of knowledge on the vertical and lateral ranges and characteristics of prospective zones (PZ) within the Lower Paleozoic unconventional hydrocarbon systems in the Baltic-Podlasie-Lublin Basin (Poland). The PZ were identified within the prospective formations based on rigorously determined criteria with the application of stratigraphic, sedimentological, mineralogical, petrographic, geochemical, petrophysical, and geomechanical studies, and interpretations of borehole logs. Archival geological data and information acquired from boreholes drilled recently in concession areas have also been applied in the interpretations. Following these criteria, four prospective zones have been distinguished. The deposits encompass partly or almost completely the Piaśnica, Sasino, and Jantar formations and the lower part of the Pelplin Formation. The characteristic feature of the Lower Paleozoic deposits at the East European Craton (EEC) margin in Poland is the diachronous appearance of the Sasino and Jantar black shale formations from west to east. The Baltic area is most prospective for the occurrence of unconventional hydrocarbon reservoirs in shale formations, specifically the Łeba Elevation, where all 4 prospective zones have been distinguished. The occurrence of liquid and gaseous hydrocarbons is expected in all zones. Due to the very high TOC content and geochemical characteristics, the Piaśnica Formation within PZ1 is the main petroleum source rock in the Polish part of the Baltic Basin. PZ2 (partly corresponding to the Sasino Formation) present in a large part of the Baltic Basin, is the next important prospective unit, despite not being uniform. PZ3 within the Jantar Formation was distinguished only on a limited area of the Łeba Elevation. Due to the low content of organic matter, the Lublin area is characterized by the lowest hydrocarbon potential. However, low values of that parameter are compensated by a greater thickness and lateral range of PZ4, partly corresponding to the Pelplin Formation. Comparison with other areas within the Lower Paleozoic Baltic Basin reveals the occurrence of shale deposits that may constitute a potential source of hydrocarbons, and that demonstrate diachronism. Towards the east and south-east, ever younger deposits possess the potential for hydrocarbon accumulations. In Poland, in the western part of EEC, these are: the Furongian and the Lower Tremadocian Piaśnica Formation, the Sandbian and Katian Sasino Formation and the Lower/Middle Llandovery (Rhuddanian and Aeronian) Jantar Formation. In the central part of the Baltic Basin (Lithuania), these are the Upper Ordovician and Aeronian shale successions. In the southeastern part of the basin (Ukraine), the Ludlow strata are considered to be the most promising in terms of the potential unconventional hydrocarbons accumulations.