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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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Estymacja czasu interwałowego z profilowań geofizyki otworowej metodą sieci neuronowych

Gąsior I., Reicher B.

Nafta-Gaz

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2014

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R. 70, nr 11

765--770

PL

Celem pracy jest wykorzystanie metody sieci neuronowych do określenia czasów interwałowych ΔT, niezbędnych do ilościowej oceny zawartości węgla organicznego (TOC % wag.) metodą CARBOLOG. Technika ta wymaga zastosowania dwóch podstawowych profilowań geofizycznych: oporności i akustycznego. Przegląd archiwalnych profilowań geofizycznych w odwiertach poszukiwawczych przemysłu naftowego i wierceniach badawczych Państwowego Instytutu Geologicznego z obszaru platformy prekambryjskiej wykazał duże zróżnicowanie ich jakości. W licznych otworach wiertniczych profilowania te nie zostały wykonane lub nie zachowały się. Z wytypowanych ostatecznie 10 odwiertów w sześciu nie wykonano profilowania akustycznego, a do estymacji czasu interwałowego wykorzystano sieci neuronowe. Przetestowano wiele typów sieci, dla różnych zmiennych wejściowych. Uzyskano wysokie współczynniki korelacji (R: 0,76÷0,97) pomiędzy wartościami czasu interwałowego otrzymanego metodą sieci neuronowych i z profilowania akustycznego. Potwierdzono tym samym poprawność metody estymowania czasu interwałowego z wykorzystaniem sieci neuronowych. Technikę tę można zastosować w odwiertach o podobnym profilu stratygraficznym, nawet w skali całych basenów.

EN

The goal of this paper is to present the use of the neural network method to estimate interval times ΔT. Interval times ΔT are essential for quantitative estimation of TOC with the use of the Carbolog method. This method requires the application of two basic geophysical logs: electrical and acoustic resistance. A review of archival geophysical logs in exploratory boreholes in the oil industry and research boreholes of the National Geological Institute in the Precambrian platform showed great diversity in their quality. In numerous boreholes the logs were not performed or were not preserved. Out of the ten boreholes eventually selected, acoustic log was not performed in six and for the assessment of the interval time the method of neural network was applied. Many types of networks were tested, for various input variables. High values of correlation coefficient were obtained (R: 0.76÷0.97) between the values of the acoustic time received by the method of neural network and the acoustic log. Thus, the correctness of the method of the acoustic log with the use of neural network was confirmed. The technique of neural network may be used in boreholes with a similar stratigraphic profile, even with respect to entire basins.

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Geological and physical-chemical characteristics of Lower Paleozoic deposits of Volhyno-Podillya, Western Ukraine

Kurovets I., Drygant D., Naumko I., Kurovets S., Koltun Y.

Biuletyn Państwowego Instytutu Geologicznego

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2012

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nr 449

119--130

EN

The 340 to 1102 m thick multi-facies sequence was deposited during the Silurian at the Volhyno-Podillya margin of the East European Platform. The open shelf facies bordered from the west by a barrier formed by reefs, bioherms, crinoids, or by banks of detrital sediments (at the boundary of the lagoon and the open sea). Lagoonal deposits are represented by thin intercalations of sedimentary dolomites, sometimes with intercalations of organogenic limestones, marls, argillites, gypsum and anhydrite. Within the open shelf and slope facies, marls, lumpy clayey limestones and argillites are prevailing. A zone of reefal buildups has a rather complicated and insufficiently investigated structure. The exclusively terrigenous deposits of the submerged part of the continental slope form the entire Silurian sequence in the central part of the L’viv Depression and in the Carpathian Foredeep. Open porosity of the Silurian argillites vary from 0.6 to 2.4% and they are almost impermeable (less than 0.001 μm2•10–3). Volume weight ranges between 2.64 and 2.8 g/cm3. Natural radioactivity of rocks varies from 9 to 18 mcR/hr, apparent electric resistance is 20–154 Ohmm, interval time of longitudinal waves spreading is 126–365 μcs/m. TOC content, determined in 21 samples using the thermal analysis, varies from 0.75 to 2.38%. The composition of volatiles of fluid inclusions and closed pores of argillites shows the predominance of methane (up to 100 vol. %). In deeper horizons, carbon dioxide, nitrogen and ethane (a few percent) appear.

PL

Zróżnicowane facjalnie utwory syluru, miąższości od 340 do 1102 m, były deponowane na wołyńsko-podolskiej krawędzi platformy wschodnioeuropejskiej. Bariera budowana przez rafy, biohermy i ławice materiału detrytycznego graniczyła na zachodzie z facjami otwartego szelfu. Na wschód od tej bariery, w lagunie, tworzyły się osady dolomitowe z przeławiceniami organogenicznych wapieni, margli, iłowców, gipsu i anhydrytu. Osady szelfu i skłonu są reprezentowane głównie przez margle i ilaste wapienie gruzełkowe oraz argility. Strefa bariery rafowej ma dość skomplikowaną i jeszcze niedostatecznie rozpoznaną budowę. Osady terygeniczne występują tylko w zanurzonym odcinku skłonu kontynentalnego w centralnej części depresji lwowskiej oraz w podłożu zapadliska przedkarpackiego. Efektywna porowatość argilitów sylurskich wynosi od 0,6 do 2,4% i są one prawie nieprzepuszczalne (mniej niż 0,001 μm2ּ10–3). Gęstość objętościowa waha się pomiędzy 2,64 i 2,8 g/cm3. Promieniotwórczość naturalna skał sięga od 9 do 18 mcR/h, a pozorna oporność właściwa wynosi 20–154 Ohmm, czas interwałowy rozchodzenia się fal podłużnych – 126–365 μcs/m. Zawartość TOC, określona w 21 próbkach z wykorzystaniem analizy termicznej, waha się od 0,75 do 2,38%. Skład substancji lotnych z inkluzji fluidalnych i zamkniętych porów w argilitach wykazuje dominację metanu (do 100% obj.). W głębszych horyzontach pojawiają się dwutlenek węgla, azot i etan (kilka procent).

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Reservoir parameters of lithostratigraphic successions of the lower Paleozoic strata in the Polish part of the Baltic region based on laboratory studies and well logs

Semyrka G., Jarzyna J., Pikulski L., Kamierczuk M., Semyrka R.

Geological Quarterly

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2010

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Vol. 54, No 2

227-240

EN

For lithostratigraphic successions of the lower Paleozoic strata in the Polish part of the Baltic Sea between the Slupsk Block and Courland Block, assessment of petrophysical properties was carried out with the use of mercury porosimetry and well logging results. The porosimetric measurements allowed to determine critical rock parameters and to distinguish genetic types of reservoirs. To complete the information on reservoir parameters, available well logs were used. The logs allowed identification of Cambrian strata in boreholes and the distinguishing of several lithostratigraphical units. Results of the porosimetric measurements demonstrated the strongly heterogeneous character of the pore space in the Cambrian rocks, with generally very weak reservoir properties. Fractured and porous-fractured rock space is a principal feature here. Well log anomalies confirmed the diversified lithological development of the Cambrian profile and the somewhat better reservoir parameters of rocks of the Paradoxides paradoxissimus Superzone and the shaly character of the Eccaparadoxides oelandicus Superzone. From the point of view of volumes of potential hydrocarbon accumulations, the capacity of the Cambrian deposits is low, but this is a basic feature of reservoir rocks with fractured and fractured-porous space.

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Outline of the lithology and depositional features of the lower Paleozoic strata in the Polish part of the Baltic region

Podhalaska T., Modliski Z.

Geological Quarterly

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2010

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Vol. 54, No 2

109-121

EN

Lower Paleozoic deposits have been noted in the western part of the Baltic Depression belonging to the Precambrian platform as well as in the Koszalin-Chojnice Zone that represents a hypothetical fragment of the Caledonian fold and thrust belt. Generally, the boundary between these regions is considered to run along faults belonging to the Teisseyre-Tornquist Zone. The deposits have been widely recognized in the East European Craton, and their entire lithological column has been drilled through in on- and offshore boreholes. New constructed lithofacies-thickness maps have updated the lithofacies diversity and thickness changes of the Ediacaran-lower Paleozoic deposits. The sedimentary infill of the Baltic Basin begins with deposits of the arnowiec Formation ascribed to the uppermost Ediacaran and lowermost Cambrian. The upper part of the Lower Cambrian comprises sandstones and mudstones and the Middle Cambrian is made of sandstones, mudstones and claystones. Upper Cambrian to Tremadocian strata are represented by dark bituminous shales. Arenigian to Ashgillian deposits are developed as thin calcareous-muddy deposits. Silurian strata represent a thick (over 3000 m) succession of siltstones and shales with subordinate calcareous intercalations in the upper part of the succession (Pridoli). In the Koszalin-Chojnice Zone only, fragments of tectonically disturbed Ordovician and Silurian shales and siltstones have been recognized.

6

Origin of oils accumulated in the Middle Cambrian reservoirs of the Polish part of the Baltic region

Kowalski A., Więcław D., Kotarba M. J.

Geological Quarterly

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2010

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Vol. 54, No 2

205-216

EN

We have examined 21 samples of crude oils accumulated in the Middle Cambrian sandstone reservoirs from the Polish part of the Baltic region. All the crude oils have similar parameters and indices, which suggests generation from the same source rock. Evaporative fractionation and biodegradation processes were detected in oil collected from the B4-N1/01 borehole. All crude oils have high gravities and low-sulphur contents, less than 0.3 wt.%, which suggests that their source rock contained low-sulphur kerogen deposited in a clastic environment. A low asphaltenes content (below 0.3 wt.%) and high saturate/aromatic hydrocarbon ratios indicate long migration distances or high thermal maturities. The longest migration distance was probably attained by oils from the arnowiec and B16 deposits. The biomarker data indicate an algal origin for the source organic matter deposited under conditions of clastic sedimentation. The stable carbon isotope data support this observation. The maturity of the oils analysed varies from ca. 0.75 to ca. 1.05% on the vitrinite reflectance scale. Unlike the B6, B16, Dbki and arnowiec accumulations, oils from the B3 and B4 accumulations reveal the lowest maturity.

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Hydrocarbon generation/expulsion modelling of the lower Paleozoic potential source rocks in the Gryfice and Kolobrzeg blocks (NW Poland)

Wróbel M., Kosakowski P., Poprawa P.

Geological Quarterly

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2010

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Vol. 54, No 2

183-196

EN

The lower Paleozoic source rocks in the offshore part of the Gryfice and Kolobrzeg blocks (NW Poland) were studied through geochemical data and numerical modelling. The geochemical study revealed a presence of effective source rocks in Caradocian strata, but with low hydrocarbon potential. The remaining lower Paleozoic source rock horizons were not documented by core samples. The timing of hydrocarbon generation and expulsion was modelled for the K1-1/86 and L2-1/87 boreholes located in the Gryfice and Kolobrzeg blocks, respectively. 1-D and 2-D modelling indicated that in the Kolobrzeg Block the onset of petroleum generation occurred at the end of the Silurian and the beginning of the Devonian. Source rocks in the Gryfice Block reached the early stage of oil generation at the beginning of the Permian and generation processes were completed by the end of the Triassic. Migration of hydrocarbons from source rocks began in the Carboniferous in both the Gryfice and Kolobrzeg blocks and lasted to the end of the Mesozoic. During hydrocarbon migration, an intensive dispersion process was observed, caused by leaking along the fault planes. The modelling revealed that hydrocarbons may have accumulated in Devonian reservoirs. The lack of any discovered accumulations could be the result of hydrocarbon dispersion caused by tectonic deformation and intense vertical fault block movements.

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Hydrocarbon generation and expulsion modelling of the lower Paleozoic source rocks in the Polish part of the Baltic region

Wróbel M., Kosakowski P., Poprawa P.

Geological Quarterly

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2010

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Vol. 54, No 2

241-256

EN

The burial history, thermal maturity, and timing of hydrocarbon generation of four source rock successions were modelled: the Middle Cambrian, the Upper Cambrian-Tremadocian, the Upper Ordovician (Caradocian) and the lower Silurian (Llandovery and Wenlock). The 1-D modelling was carried out in profiles of eight boreholes throughout the western Baltic region. Four selected boreholes are located offshore: A8-1/83, A23-1/88, B6-1/82 and B4-2A/02, and four onshore: Bialogóra 3, Dbki 3, Leba 8 and arnowiec IG 1. The thermal maturity of source rocks is the highest in the deeper buried western part of the basin and decreases from the west to the east and north-east towards the basin margins. The lower Paleozoic source rocks contain oil-prone Type-II kerogen. The modelling indicated that the onset of petroleum generation from the lower Paleozoic source rocks occurred from the Early Devonian through the early Carboniferous period. The peak of hydrocarbon generation took place from the Late Devonian to the Tournaisian. The majority of hydrocarbons generated were expelled during the latest Early Devonian and Carboniferous, and oil has not been expelled from source rock only in the eastern offshore part of the basin.

9

Habitat and hydrocarbon potential of the lower Paleozoic source rocks in the Polish part of the Baltic region

Kowalski A., Więcław D., Grotek I., Kotarba M. J., Kosakowski P.

Geological Quarterly

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2010

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Vol. 54, No 2

159-182

EN

The quantity, genetic type and maturity of organic matter dispersed in the Lower Cambrian to the uppermost part of the Silurian (Pridoli) sequence of the Polish part of the Baltic region was determined based on the results of geochemical analyses of a total of 1377 rock samples collected from 38 onshore and offshore boreholes. The best source rocks were found in the Upper Cambrian-Tremadocian succession where present and initial total organic carbon (TOC) contents are up to ca. 18 and 20 wt.%, respectively. Caradocian (Ordovician) strata can be considered as an additional source of hydrocarbons. In the individual boreholes median present and initial TOC contents vary from 0.5 to 3.3 wt.% and from 1 to 6 wt.%, respectively. The Llandovery (Silurian) strata reveal moderate and locally high hydrocarbon potential of the source rocks. The present TOC content reaches locally 10 wt.% (usually 1-2 wt.%). Another source of hydrocarbons can be clayey intercalations within the Middle Cambrian strata. Their organic matter content rarely exceeds 1 wt.%, being often a result of advanced organic matter transformation. In all lower Paleozoic strata investigated from the Polish part of the Baltic region oil-prone, low-sulphur Type-II kerogen occurs, deposited in anoxic or sub-oxic conditions. The maturity of all source rocks changes from the initial phase of the low-temperature thermogenic processes in the northeastern part to the overmature stage in the southwestern part of the study area.

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Geological section through the lower Paleozoic strata of the Polish part of the Baltic region

Pokorski J.

Geological Quarterly

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2010

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Vol. 54, No 2

123-130

EN

The present-day structural pattern of the Baltic Depression developed due to superimposition of three main deformation phases: syn-Caledonian (after the Silurian), syn-Variscan (at the end of Carboniferous and beginning of Permian) and syn-Alpine (latest Mesozoic or earliest Cenozoic). The major restructuring of the area occurred as a result of syn-Variscan deformation that took place in latest Carboniferous and earliest Permian times. Most of the faults developed or became reactivated probably at that time. Syn-Alpine deformation manifested itself relatively weakly, mainly by reactivation of some pre-existing faults.

11

2-D modelling of petroleum processes of the lower Paleozoic strata in the Polish part of the Baltic region

Wróbel M., Kosakowski P.

Geological Quarterly

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2010

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Vol. 54, No 2

257-266

EN

2-D modelling of hydrocarbon generation, expulsion, migration and accumulation processes was carried out for the four (Middle Cambrian, Upper Cambrian-Tremadocian, Caradocian and Llandovery) source rock horizons. The petroleum potential of these source rocks is different, the highest being observed in the Upper Cambrian-Tremadocian horizon and the lowest in the Middle Cambrian one. The maturity of organic matter within these source units increases from the north-east to the south-west of the Polish part of Baltic region. The petroleum generation from these source rocks was highest in the Darlowo and Slupsk blocks as well as in the onshore part of the Leba Block. Expulsion took place mainly from the Upper Cambrian-Tremadocian source rocks and these rocks sourced almost all hydrocarbons accumulated within the Middle Cambrian sandstone reservoirs. Migration of hydrocarbons proceeded along fault zones. Almost all petroleum processes in the study area took place between the end of the Pridoli and the end of the Carboniferous. Moreover, during the Permian and the Mesozoic, part of the hydrocarbons remigrated within the reservoir. This process changed the setting and the volume of hydrocarbon accumulations. It was caused by the tectonic rebuilding of the basin and, in most cases, it led to the modification of accumulation range or to the dispersion of hydrocarbons.