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Petrographic characteristics of the Ordovician and Silurian deposits in the Baltic Basin (N Poland) and their relevance for unconventional hydrocarbon accumulations

Kuberska Marta, Sikorska-Jaworowska Magdalena, Kozłowska Aleksandra, Podhalańska Teresa

Geological Quarterly

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2021

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Vol. 65, No. 3

art. no. 44

EN

The Ordovician and Silurian deposits in the Baltic Basin are represented by siltstones, mudstones, limestones, marls, sandstones and, most commonly, claystones with a markedly shaley structure. Claystones that are particularly rich in organic matter are considered as potential reservoirs for shale gas accumulations. Samples from 11 boreholes, including core samples of the Piaśnica, Słuchowo, Kopalino, Sasino, Prabuty, Jantar, Pelplin and locally Pasłęk, Kociewie and Puck formations, were analysed by optical microscopy, cathodoluminescence (CL), scanning electron microscopy (SEM) and energy-dispersive spectrometry and X-ray diffraction analyses (XRD). The Piaśnica, Sasino, Jantar, Pasłęk and Pelplin formations are characterized locally by a dominance of black bituminous claystones with a high content of organic matter, and a generally consistent clay mineral composition. Individual samples only show variations in silt fraction and carbonate content. Very important is the negligible proportion of swelling minerals in the clay fraction; the percentage of smectite in the mixed-layered illite/smectite minerals does not exceed 15%. It is important for the rocks to have adequate [SiO2 >10%; Quartz (Q) + Feldspars (Fs) + Carbonates >40%] brittleness. The content of quartz, feldspars and carbonates (here >40%) suggests that the claystones are susceptible to hydraulic fracturing. The claystones show micropores between detrital grains, between the flakes of clay minerals, within pyrite framboids, and organic matter and secondary micropores within grains.

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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

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2020

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Vol. 64, No. 2

342--376

EN

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.

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Microphytoplankton from middle palaeolatitudes of the Southern Hemisphere : a record from climate change strata of Baltica’s O/S boundary

Masiak Monika, Stempień-Sałek Marzenna, Podhalańska Teresa

Geological Quarterly

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2020

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Vol. 64, No. 1

86--103

EN

In the present study, data on the diversity of acritarch and prasinophyte microphytoplankton were collected from Ordovician-Silurian transitional strata at three different geological localities in Poland: southern part of the Holy Cross Mountains (Małopolska Block, southern Poland), East European Platform (Baltica), and Koszalin-Chojnice Zone (NW Poland). The material represents the mucronata (trilobite) to vesiculosus (graptolite) biozones. The Ordovician microphytoplankton assemblages are characterized by low frequency and low diversity: up to 110 specimens and 12 genera per slide, in contrast to Silurian ones that are more frequent and more diverse - >3000 specimens and 16 genera per slide (diversity at the species level is also higher). Throughout the Ordovician part of the succession, typical Ordovician genera occur, such as Acanthodiacrodium, Ordovicidium, Orthosphaeridium and large Baltisphaeridium, together with isolated occurrences of typical Silurian genera, especially in the upper part of the Hirnantian (e.g., Diexallophasis). The Silurian assemblages are typified by high frequency of prasinophytes followed by typical Siluran acritarchs: Tylotopalla, Ammonidium, Domasia and Oppilatala. The palynological material from Poland is compared with material known from other localities: the Rapla and Valga boreholes (Estonia) and Anticosti Island (Canada), as well as others placed in different palaeocontinents and different bathymetric zones. Palynological assemblages obtained from Polish material confirm that bathymetry played the key role in taxonomic diversification of the microphytoplankton assemblage. This supports the existing models of distribution: dominance of prasinophytes (leiospheres) and cryptospores is characteristic for shallow-water environments. In deeper water, dominance of acanthomorphs is observed. In the deepest-water zones - mixed assemblages occur. For the Holy Cross Mountains, microphytoplankton frequency is compared with a TOC curve in the same interval.

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Ordovician–Silurian lithostratigraphy of the East European Craton in Poland

Porębski Szczepan, Podhalańska Teresa

Annales Societatis Geologorum Poloniae

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2019

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Vol. 89, No. 2

95--104

EN

This paper deals with the lithostratigraphic correlation of the Ordovician-Silurian succession between the Baltic, Podlasie and Lublin basins, located on the SW slope of the East European Craton. The correlation is based on previous lithostratigraphic classifications, which are modified here to include the results of recent biostratigraphic and sedimentological work performed on several new wells. The authors propose to extend the Sasino Formation for the entire upper Darriwilian-lower Katian mudstone sheet that is traceable in all basins. It is recommended that the Jantar Bituminous Claystone Member (late Hirnantian-Aeronian) of the Pasłęk Formation be elevated to the rank of formation and the name Pasłęk Mudstone Formation be retained for the late Aeronian-Telychian, rhythmic alternations of black, laminated mudstones and greenish, bioturbated mudstones. Moreover, the authors suggest that the top of the Kociewie Formation (Sheinwoodian-Ludfordian) be placed at the upper boundary of the Reda Member (latest Ludfordian), which shows much wider lateral persistence than previously was thought.

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Graptolite biostratigraphy and dating of the Ordovician–Silurian shale succession of the SW slope of the East European Cratond

Podhalańska Teresa

Annales Societatis Geologorum Poloniae

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2019

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Vol. 89, No. 4

429--452

EN

This paper deals with the graptolite biostratigraphy and age determination of the Ordovician and Silurian lithological successions of the Baltic, Podlasie and Lublin basins that existed during the early Palaeozoic on the SW slope of the East European Craton. The biostratigraphic research described was conducted on core material coming from old boreholes and cores from several new wells. Graptolite zones were identified and the chronostratigraphic succession was constrained, with the depths to the stratigraphic units, especially those considered prospective for petroleum, being determined in the individual borehole sections. Old local stratigraphic schemes of the Silurian used for many years in the Polish geological literature are correlated with the standard schemes. The most complete succession of graptolite zones, both in the Ordovician and the Silurian, is observed in the Baltic region. The number of stratigraphic gaps increases towards the east and southeast of the regions. The stratigraphic range of the Sasino Shale Formation decreases in this direction; in the Podlasie and Lublin regions, it comprises only the Katian Stage. The stratigraphic range of the Jantar Formation in the western part of the area spans not only the Rhuddanian but also part or the whole of the Aeronian. In the Podlasie and especially the Lublin regions, sedimentation of the Jantar Formation began in the latest Rhuddanian–Aeronian. A large stratigraphic gap, spanning part or the whole of the Llandovery and increasing eastwards, was documented in the Podlasie-Lublin region. The biostratigraphic research allowed a more precise constraint on the temporal and spatial extent of erosion of Pridoli deposits and the beginning of coarse-grained, siliciclastic sedimentation (Kociewie Formation) in the Baltic Basin.