Maciej J. Kotarba

Assessment of hydrocarbon source rock potential of Polish bituminous coals and carbonaceous shales

Abstract We analyzed 40 coal samples and 45 carbonaceous shale samples of varying thermal maturity (vitrinite reflectance 0.59% to 4.28%) from the Upper Carboniferous coal-bearing strata of the Upper Silesian, Lower Silesian, and Lublin basins, Poland, to evaluate their potential for generation and expulsion of gaseous and liquid hydrocarbons. We evaluated source rock potential based on Rock-Eval pyrolysis yield, elemental composition (atomic H/C and O/C), and solvent extraction yields of bitumen. An attempt was made to relate maceral composition to these source rock parameters and to composition of the organic matter and likely biological precursors. A few carbonaceous shale samples contain sufficient generation potential (pyrolysis assay and elemental composition) to be considered potential source rocks, although the extractable hydrocarbon and bitumen yields are lower than those reported in previous studies for effective Type III source rocks. Most samples analysed contain insufficient capacity for generation of hydrocarbons to reach thresholds required for expulsion (primary migration) to occur. In view of these findings, it is improbable that any of the coals or carbonaceous shales at the sites sampled in our study would be capable of expelling commercial amounts of oil. Inasmuch as a few samples contained sufficient generation capacity to be considered potential source rocks, it is possible that some locations or stratigraphic zones within the coals and shales could have favourable potential, but could not be clearly delimited with the number of samples analysed in our study. Because of their high heteroatomic content and high amount of asphaltenes, the bitumens contained in the coals are less capable of generating hydrocarbons even under optimal thermal conditions than their counterpart bitumens in the shales which have a lower heteroatomic content.

Composition and origin of coalbed gases in the Lower Silesian basin, southwest Poland

Abstract Coalbed gases in the Lower Silesian Coal Basin (LSCB) of Poland are highly variable in both their molecular and stable isotope compositions. Geochemical indices and stable isotope ratios vary within the following ranges: hydrocarbon (CHC) index CHC=CH4/(C2H6+ C3H8) from 1.1 to 5825, wet gas (C2+) index C2+=(C2H6+ C3H8+ C4H10+ C5H12) / (CH4+ C2H6+ C3H8+ C4H10+ C5H12) 100 (%) from 0.0 to 48.3%, CO2–CH4 (CDMI) index CDMI=CO2/(CO2+ CH4) 100 (%) from 0.1 to 99.9%, δ13C(CH4) from −66.1 to −24.6‰, δD(CH4) from −266 to −117‰, δ13C(C2H6) from −27.8 to −22.8‰, and δ13C(CO2) from −26.6 to 16.8‰. Isotopic studies reveal the presence of 3 genetic types of natural gases: thermogenic (CH4, higher gaseous hydrocarbons, and CO2), endogenic CO2, and microbial CH4 and CO2. Thermogenic gases resulted from coalification processes, which were probably completed by Late Carboniferous and Early Permian time. Endogenic CO2 migrated along the deep-seated faults from upper mantle and/or magma chambers. Minor volumes of microbial CH4 and CO2 occur at shallow depths close to the abandoned mine workings. “Late-stage” microbial processes have commenced in the Upper Cretaceous and are probably active at present. However, depth-related isotopic fractionation which has resulted from physical and physicochemical (e.g. diffusion and adsorption/desorption) processes during gas migration cannot be neglected. The strongest rock and gas outbursts occur only in those parts of coal deposits of the LSCB which are dominated by large amounts of endogenic CO2.

Pre-Neogene evolution of the Western Carpathians: Constraints from the Bochnia-Tatra Mountains section (Polish Western Carpathians)

On the basis of field studies and subsurface data, this first balanced transect crosses most of the Carpathian foreland basin and the entire Polish Western Carpathian thrust units (Outer flysch nappes, Pieniny Klippen Belt, and Inner Carpathian Tatric thrust sheets). It shows that (1) me Outer Carpathians are made up of several flysch units whose internal structure is strongly controlled by initial thicknesses, whereas the thin flysch successions are strongly deformed by tight folds and include several imbricated thrust sheets; by contrast, the thick flysch successions are less deformed and accreted in slightly imbricated thrust sheets; and (2) the Inner Carpathians are structured in an antiformal stack of basement thrust sheets. The unfolding of this cross section shows that the post-middle Oligocene shortening in the European foreland platform and Outer Carpathians exceeds 180 km. In the substratum, most of this shortening seems to be solved by basement consumption vertically beneath the suture zone of the Pieniny Klippen Belt. Additional basement shortening took place also (1) in the Inner Carpathians, where, during the Neogene, buried basement thrust sheets were piled up to form an antiformal stack, and (2) beneath the inner zones of the Outer Carpathians. Palinspastic restoration of the cross section reflects two well-differentiated zones prior to the late Oligocene-late Miocene compression: (1) the present Inner Carpathians and the Pieniny Klippen Belt, characterized by a Late Cretaceous thrust belt unconformably overlain by an undeformed Palaeogene cover, and (2) the Outer flysch Carpathians, in which pre-upper Oligocene configuration comprised a typical foreland basin flexed toward the SSW, with a system of NW trending highs and troughs.

Oil/oil and oil/source rock correlations in the Carpathian Foredeep and Overthrust, south-east Poland☆

Abstract The chemical composition of 35 crude oils and the extracts of potential source rock samples from south-east Poland were studied in detail by geochemical methods in order to understand their genetic relationships. Twenty-six oils, including three seep samples, were collected from Cretaceous to Oligocene reservoirs within the Carpathian Overthrust. Nine oils originated from Carboniferous to Miocene reservoirs within the Carpathian Foredeep. The rock samples studied were selected after Rock-Eval pyrolysis screening of a large suite of samples and consist of one Lower Cretaceous sample and five Oligocene Menilite shale samples (from three different outcrop locations all within the Carpathian Overthrust). Geochemical fingerprinting indicates at least two families of crude oils: the first, represented only by one oil, has no specific characteristics except for a light carbon isotope composition; the second family is characterized by the presence of 28,30-dinor-hopane, oleanane and a highly-branched isoprenoid C25 alkane. Within this latter family four subfamilies were recognized: (A) 19 oils having the aforementioned characteristics, (B) seven oils similar to subfamily A, but with a relatively high sulphur content, (C) one oil with high abundance of higher-plant derived triterpanes, and (D) seven oils with abundant 28,30-dinor-hopane. Although maturity influences the relative abundance of 28,30-dinor-hopane, it suggested that subfamilies A, B, and C had an initial low 28,30-dinor-hopane content, whereas subfamily D an initial high 28,30-dinor-hopane content. Only one oil of subfamily A could potentially be a high maturity counterpart of subfamily D. A Palaeozoic source rock is suggested for the first family, and the second family, including the majority of the pils from the Carpathian Foredeep, is most likely derived from the Oligocene Menilite Shales. An oil/source rock relationship with the Menilite Shale is supported by the presence (although not in all samples studied) of 28,30-dinor-hopane, oleanane or its precursors, and the highly-branched isoprenoid alkane. The strong facies variations observed within this shale gave rise to the different types of crude oils in the second family.

The Origin and Habitat of Hydrocarbons of the Polish and Ukrainian Parts of the Carpathian Province

Multiple petroleum systems occurring in different tectonic elements of the Polish and Ukrainian parts of the Flysch Carpathians, their foredeep, and the Paleozoic–Mesozoic basement have been identified and characterized using various geochemical methods. The Carpathian flysch sequence, containing the main oil fields in the area, contains two main potential source rock intervals: the Early Cretaceous and Oligocene. The Oligocene Menilite shales, which are widespread in the Polish and Ukrainian parts of the Carpathian flysch belt, contain high-quality source rocks, with mainly type II kerogen and high petroleum potential. A suitable tectonic position in several units of the flysch belt, especially in its frontal nappes of the Ukrainian part, provided the maturation level of this series, corresponding to different parts of the oil window. Modeling of hydrocarbon generation and expulsion in Menilite rocks shows that these processes are related mainly to Miocene overthrusting. Geochemical studies of oils from different fields occurring in the flysch sequence show that they belong to the same family. The presence of oleanane probably indicates that they have been generated from Menilite rocks. Lower Cretaceous organic-rich rocks, which contain mainly type II and III kerogen with good petroleum potential and a maturation level corresponding to the oil window, should be considered as another important potential source rock sequence in both the Polish and Ukrainian Carpathian flysch belt. The autochthonous Miocene nonfolded molasse sequence contains most of the gas fields in the Polish and Ukrainian Carpathian Foredeep. Geochemical studies of Badenian and Sarmatian strata show that they contain sufficient amounts of immature terrestrial organic matter, which generated methane-rich microbial gases. Molecular and isotopic compositions of natural gases from Miocene reservoirs confirm that they were produced during microbial carbon dioxide reduction. Molecular and stable isotope compositions of gases from Paleozoic–Mesozoic reservoirs of the Polish part of the basement show that they were generated by both microbial and thermogenic processes. Gas from the Lachowice field in Devonian rocks is a typical nonassociated thermogenic gas, generated from type III kerogen with a high degree of maturation. This gas probably migrated from Carboniferous source rocks. The oils accumulated in Upper Cretaceous and Upper Jurassic reservoirs in the Polish part and, southeast of the Ukrainian part of the basement, contain oleanane and other specific biomarkers and belong to the same geochemical family. They were probably generated from the Oligocene flysch rocks and Middle Jurassic beds.

A stable carbon isotope and biological marker study of Polish bituminous coals and carbonaceous shales

Abstract Biological marker and carbon isotopic compositions of coals and carbonaceous shales from the Upper Carboniferous strata of the Upper Silesian (USCB), Lower Silesian (LSCB), and Lublin (LCB) coal basins were determined to assess depositional conditions and sources of the organic matter. n -Alkane, sterane, and isoprenoid distribution, and carbon isotope ratios are consistent with an origin from higher plants. In some cases, pristane/phytane (Pr/Ph) ratios of carbonaceous shales (roof and floor shales) are 29 stereoisomers, typical, but not conclusive, of higher plant origin. Carbonaceous shales exhibit a wider range of sterane composition, suggesting local, significant input of algal organic matter. Significant amounts of benzohopanes and gammacerane are present in some coals. Although benzohopanes are present at least in small amounts in samples from many different environments, they have been reported to occur most commonly in marine environments. The present study seems to provide the first example where benzohopanes have been reported in significant amounts in terrestrial organic matter. Gammacerane is abundant in rocks or sediments deposited in carbonate or highly saline marine environments. The finding of high gammacerane concentrations in the coals expands the depositional settings in which it has been observed and questions its utility as an independent indicator of hypersaline carbonate environments. Stable carbon isotope composition of coals, and type III kerogen in carbonaceous shales as well as correlation of stable carbon isotope composition of saturated and aromatic hydrocarbons in carbonaceous shales from both the USCB and the LSCB indicate terrigenous origin. Bitumens are always co-genetic with associated coals and kerogens. Isotopic data reveal that Sofers genetic classification of oils is not applicable to organic matter in coals.

Source rock habitat and hydrocarbon potential of Oligocene Menilite Formation (Flysch Carpathians, Southeast Poland): an organic geochemical and isotope approach

Geochemical and isotope methods have been used to analyse the hydrocarbon potential and petroleum generation characteristics of the Oligocene Menilite Formation, the most important petroleum source rock in the overthrust part of the Carpathian foreland basin in SE Poland. The data show a large variability in quantity (up to 18% TOC), quality (type II and II/III) and carbon isotope composition of the organic matter in samples of different lithology and from different stratigraphic and tectonic settings. These differences reflect distinct sedimentary and tectonic histories of individual sub-basins. The maturity in the outer tectonic units is very low (Tmax < 420°C, Ro < 0.35%) but increases towards the inner nappes and also laterally to the SE. The variability of the kinetic parameters indicates the likely occurrence of multiphase hydrocarbon generation. The Menilite Formation forms a very good source rock in the complex petroleum system of the Carpathian overthrust belt.

Isotopic geochemistry and habitat of the natural gases from the Upper Carboniferous Žacleř coal-bearing formation in the Nowa Ruda coal district (Lower Silesia, Poland)

The Nowa Ruda coal district is located in the SE part of the Lower Silesian Coal Basin. The analysed coals have vitrinite reflectance from 1.12 to 1.56% and δ13C values from −24.6 to −23.2%. Natural gases accumulated in coal seams reveal considerable variability of molecular and isotopic compositions. Geochemical indices and stable isotope ratios vary in the following ranges: C2+ wet gas index from 0.6 to 40.7%; carbon dioxide-methane index (CDMI) from 1.9 to 99.9%; δ13C(methane) from −66.1 to −28.6%; δD(methane) from −256 to −211%; δ13C(carbon dioxide) from −24.4 to −7.0%; and δ13C(ethane) from −27.8 to −25.5%. Stable isotope studies allow distinction between thermogenic, endogenic (magmatic and/or upper-mantle derived) and probably even bacterial gases. The intensity of migration, mixing and accumulation of the natural gases of various origins appear to be variable in time and space. The variability of both the molecular and the isotopic compositions of the analysed gases probably results from the specific primary reactions active during the generation of the thermogenic gases in coal seams (decomposition of coal-seam matrix and/or cracking of n-alkanes) and/or in humic dispersed organic matter of coaly mudstones. An isotopic fractionation may also develop during the migration of the natural gases through the ultra-fine pores of coals. The results of this paper suggest that in the case of gases connected with coal seams, the existing gas classifications cannot be directly applied to their genetic interpretation.

Unique Quaternary environment for discoveries of woolly rhinoceroses in Starunia, fore-Carpathian region, Ukraine: Geochemical and geoelectric studies

In 1907, remnants of a mammoth and a woolly rhinoceros were discovered in the Pleistocene clays of an earth-wax mine in Starunia village. Then, in 1929, a nearly fully preserved woolly rhinoceros was found in the same mine. The unique combination of clays, oil, and brine into which the animals had sunk is responsible for their almost perfect preservation. During the late Pleistocene winters, when the ice and snow cover was present in the tundra “paleoswamp,” areas of infl ow of brines, oils, and hydrocarbon gases had a higher temperature, which resulted in melting and cracking of the cover, and large mammals could be trapped. Geoelectric measurements, as well as molecular and stable isotope analyses of gases in the near-surface zone within the “paleoswamp” performed in 2004–2005, reveal a few places favorable to the burial and preservation of Pleistocene vertebrates.

Thermal-maturity limit for primary thermogenic-gas generation from humic coals as determined by hydrous pyrolysis

Hydrous-pyrolysis experiments at 360°C (680°F) for 72 h were conducted on 53 humic coals representing ranks from lignite through anthracite to determine the upper maturity limit for hydrocarbon-gas generation from their kerogen and associated bitumen (i.e., primary gas generation). These experimental conditions are below those needed for oil cracking to ensure that generated gas was not derived from the decomposition of expelled oil generated from some of the coals (i.e., secondary gas generation). Experimental results showed that generation of hydrocarbon gas ends before a vitrinite reflectance of 2.0%. This reflectance is equivalent to Rock-Eval maximum-yield temperature and hydrogen indices (HIs) of 555°C (1031°F) and 35 mg/g total organic carbon (TOC), respectively. At these maturity levels, essentially no soluble bitumen is present in the coals before or after hydrous pyrolysis. The equivalent kerogen atomic H/C ratio is 0.50 at the primary gas-generation limit and indicates that no alkyl moieties are remaining to source hydrocarbon gases. The convergence of atomic H/C ratios of type-II and -I kerogen to this same value at a reflectance of indicates that the primary gas-generation limits for humic coal and type-III kerogen also apply to oil-prone kerogen. Although gas generation from source rocks does not exceed vitrinite reflectance values greater than , trapped hydrocarbon gases can remain stable at higher reflectance values. Distinguishing trapped gas from generated gas in hydrous-pyrolysis experiments is readily determined by of the hydrocarbon gases when a -depleted water is used in the experiments. Water serves as a source of hydrogen in hydrous pyrolysis and, as a result, the use of -depleted water is reflected in the generated gases but not pre-existing trapped gases.