Thermal Transformation Of Organic Matter Research Articles

Thermally induced release and generation of CO2 and C1–C4 hydrocarbons in Opalinus Clay from Mont Terri (Switzerland)

Claystone formations are candidate host rocks for high-level heat-emitting nuclear waste (HLW). Temperatures from 90 to 150 °C at the canister surface are discussed internationally as potential emplacement and storage conditions. The thermal energy emitted from waste containers will be transported into the host rock formation, accelerating chemical reactions including the release of sorbed and dissolved gases and the generation of new gases. This study investigated gas release and generation in Opalinus Clay from Mont Terri (Switzerland) at elevated temperature and pressure conditions relevant for HLW storage and beyond. Hydrous pyrolysis experiments were conducted in Dickson-type flexible gold-titanium reaction cells and gold capsules in the temperature range of 80–345 °C and at 20 MPa. CO2(g) was the predominant product, followed by C1–C4 hydrocarbons, which decrease in abundance with increasing carbon atom number. Neither CO nor H2S was detected. H2 was generated only in high temperature experiments at 315 °C and 345 °C, respectively. A combination of CO2(g) quantification, stable carbon isotopic composition data, thermodynamic calculations and aqueous fluid composition (dissolved ions, pH) demonstrated that ≥80 % of the measured CO2(g) originated from carbonate mineral dissolution. The model calculations also suggest that the fraction of CO2(aq) in DIC increases from ∼50 % at 80 °C to nearly 100 % at higher temperatures. Thermal transformation of organic matter represented an additional source for CO2(g) and was the predominant process yielding the C1–C4 hydrocarbons. Our findings stress the importance of quantitative geochemical data for the safety assessment of potential host rocks for HLW storage. We demonstrated that two sources are involved in gas release and generation at temperatures relevant for HLW storage, e.g., in the Opalinus Clay – organic matter and carbonate minerals. Our data will contribute to numerical modelling studies and the refinement of feature, events, and processes (FEP) catalogues.

Accessibility of Pores to Methane in New Albany Shale Samples of Varying Maturity Determined Using SANS and USANS

The accessibility of pores to methane has been investigated in Devonian New Albany Shale Formation early-mature (Ro = 0.50%) to post-mature (Ro = 1.40%) samples. A Marcellus Shale Formation sample was included to expand the maturation range to Ro 2.50%. These are organic matter-rich rocks with total organic carbon (TOC) values of 3.4 to 14.4% and porosity values of 2.19 to 6.88%. Contrast matching small-angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS) techniques were used to generate porosity-related data before and after pressure cycling under hydrostatic (in a vacuum and at 500 bar of deuterated methane) and uniaxial stress (0 to ca. 350 bar) conditions. Our results showed that the accessible porosity was small for the samples studied, ranging from zero to 2.9%. No correlation between the accessible porosity and TOC or mineralogical composition was revealed, and the most likely explanation for porosity variation was related to the thermal transformation of organic matter and hydrocarbon generation. Pressure caused improvements in accessible porosity for most samples, except the oil window sample (Ro = 0.84%). Our data show that densification of methane occurs in nanopores, generally starting at diameters smaller than 20 nm, and that the distribution of methane density is affected by pressure cycling.

Origin of hydrocarbon and noble gases, carbon dioxide and molecular nitrogen in the Miocene strata of the eastern part of the Polish Carpathian Foredeep: Isotopic and geological approach

Fifteen natural gas samples were collected from the autochthonous Miocene strata between Dębica and Przemyśl towns in the eastern sector of the Polish Carpathian Foredeep. The samples were analysed for the molecular and stable isotope compositions of carbon (δ13C in CH4, C2H6, C3H8, i-C4H10, n-C4H10 and CO2), hydrogen (δ2H in CH4, C2H6 and C3H8), nitrogen (δ15N in N2), and all stable isotopes of noble gases (He, Ne, Ar, Kr and Xe) in order to reveal the origin and migration pathway of these gases. Methane concentrations usually exceeded 90 vol%. Methane was mainly generated by microbial carbon dioxide reduction. The rhythmic and cyclic deposition of clays, muds and sands in the Miocene marine basin facilitated and intensified microbial processes. Microbial ethane can be produced by methanogenic Archaea from acetate via reduction. Ethane partly contains a minor component generated from early mature thermogenic process. Propane and butanes were also generated thermogenically. The hydrocarbon gases in the Miocene horizons IIA and IIIA of the Góra Ropczycka field were generated at higher maturity thermogenic process than the rest of the analysed Miocene gases probably from the Middle Jurassic type III kerogen. They migrated to the Miocene horizons from the underlying Upper Jurassic horizon IV of the same field along a fault. Carbon dioxide of the analysed Miocene gases was mainly generated by primary microbial processes. Moreover, the total carbon constrained in the analysed Miocene gases from 0.1 to 6 wt% contained mantle-derived carbon, and thus carbon dioxide mantle component. Molecular nitrogen was mainly generated during low-temperature thermal transformation of organic matter. It might also involve a relatively insignificant component released from NH4-rich illites of the clayey facies of Miocene strata and an atmospheric component delivered by recharge of air-saturated seawater to the reservoir. Inorganic fluid supply from greater lithospheric depth would not be responsible for the promotion of thermal transformation of organic matter. Molecular nitrogen from Miocene horizons in the Góra Ropczycka field was generated during the thermal transformation of organic matter of higher maturity than the rest of Miocene gases, and migrated from the Upper Jurassic horizon along a fault. Helium is dominated by its radiogenic component, with a minor contribution from the mantle. The almost constant mixing ratios of the two helium components in the natural gases from Miocene horizons of various depths suggest that He migrated from a common inorganic deep-seated source in the lithosphere. The other noble gases are dominated by atmospheric components delivered to the hydrocarbon reservoirs by recharge of air-saturated seawater, with minor nucleogenic 21Ne, radiogenic 40Ar, and sedimentary Kr and Xe contributions. The atmospheric component is isotopically fractionated for Ne, and elementally fractionated with various degrees. The ratios of radiogenic 4He to nucleogenic 21Ne or radiogenic 40Ar are higher than the crustal production ratios, suggesting fractionation during thermal release from their host minerals and/or phase related fractionation during their transport to the gas reservoirs. The striking similarity in noble gas isotopic/elemental ratios of the Góra Ropczycka gas from the Miocene horizon IIIA to the nearby reservoir in Mesozoic strata is consistent with gas migration along a fault system.

Origin and migration of oil and natural gas in the central part of the Ukrainian outer Carpathians: Geochemical and geological approach

The generation and migration processes, as well as the influence of secondary processes, on oil and natural gas accumulated in Lower Cretaceous–lower Miocene strata of the central part of the Ukrainian outer Carpathians are discussed. Type II and II/III kerogens from the Oligocene–lower Menilite beds of the Boryslav-Pokuttya nappe generated oil and natural gas mainly during the middle stage of the oil window. These hydrocarbons accumulated in the fields of the Boryslav-Pokuttya and Skiba nappes. Water washing is the dominant secondary process occurring in many accumulations, regardless of reservoir rock, whereas biodegradation is insignificant and is clearly evident only in natural gas from one seep in the abandoned Starunia ozocerite mine. All hydrocarbon gases are thermogenic and were generated from mixed organic matter containing various proportions of type II and III kerogens. Only one natural gas accumulation in the Pivnichna Dolyna field contains some microbial hydrocarbon contribution. Carbon dioxide mainly originated from thermogenic kerogen decarboxylation and sporadically from microbial processes. Molecular nitrogen was mainly generated during low-temperature thermal transformation of organic matter and could also partly originate from NH4-rich illites of the clayey facies of the Oligocene–lower Miocene Menilite beds. The integration of the geochemical data with geological setting and maturation history of source rocks enabled us to reconstruct hydrocarbon migration paths, revealing the complicated trap-filling process.

Variations of organic matter transformation in response to hydrothermal fluids: Example from the Indiana part of the Illinois Basin

Thermal maturation of organic matter in sedimentary rocks is a complex process controlled by multiple parameters. In this study, we examined the thermal history of one location in the Indiana part of the Illinois Basin. A total of 21 samples spanning the time interval from the Ordovician to the Mississippian were selected for maturity assessment and chemical structure characterization of vitrinite/vitrinite-like particles, solid bitumen, and alginite. The reflectance of vitrinite/vitrinite-like particles (VRo) reveals erratic variations with depth from 0.61% to 1.18%. Solid bitumen reflectance (SBRo), ranging from 0.43 to 0.92%, is slightly lower than VRo across this maturity range in this borehole. In addition to documenting reflectance variations with depth, variations within single organic matter particles were analyzed in the Upper Devonian New Albany Shale and Upper Ordovician Maquoketa Shale samples; these samples were targeted because they contained more organic matter than the samples from other stratigraphic units. SBRo shows significant variations within a single solid bitumen particle with a difference up to 0.81%. Significant maturity-related chemical differences within individual particles of solid bitumen and alginite were also revealed using micro-FTIR technique. An increase in temperature with depth of burial is certainly the key factor in controlling the thermal transformation of organic matter in sedimentary rocks. However, it is apparent that this mechanism alone does not explain the stratigraphic variations of VRo throughout the core and reflectance variations within individual solid bitumen and alginite particles. We suggest that the flow of hydrothermal fluids through the New Albany and Maquoketa Shale caused the observed thermal maturity anomaly. High concentrations of chlorine, vanadium, chromium, and zinc also suggest that organic matter transformation was enhanced by the flow of hydrothermal fluids in the study area.

Source rock geochemistry, petrography of reservoir horizons and origin of natural gas in the Devonian of the Lublin and Lviv basins (SE Poland and western Ukraine)

The Rock-Eval source rock characteristics, mineral composition and type-porosity of reservoir horizons, and origin of natural gas in the Devonian of the Lublin and Lviv basins are described. In the Lower Devonian, the TOC content ranges from 0.01 to 1.82 wt.% in the Lublin Basin, and from 0.01 to 0.45 wt.% in the Lviv Basin. Transformation of organic matter varies from immature in the Lochkovian (Lviv Basin) to mature and overmature in the Emsian (Lublin Basin). The organic matter contains mainly Type-II kerogen, and underwent primary and/or secondary oxidation processes. In the Middle Devonian, the TOC content varies from 0.00 to 1.63 wt.% in the Lublin Basin, and from 0.02 to 0.64 to 2.35 wt.% in the Lviv Basin. The organic matter contains mainly Type-II kerogen and is immature in the Givetian of the Lviv Basin and mature in the Eifelian of the Lviv Basin and in the Eifelian and Givetian in the Lublin Basin. In the Upper Devonian, the TOC content is from 0.02 to 2.62 wt.% in the Lublin Basin, and from 0.04 to 1.43 wt.% in the Lviv Basin. Type-II kerogen dominates in both basins. Organic matter is mature in the Upper Devonian in the Lublin Basin and in the Famennian of the Lviv Basin and overmature in the Frasnian of the Lviv Basin. The reservoir horizons in the Devonian of the Lublin and Lviv basins are developed in clastic, carbonate and sulphate rocks. Terrigenous rocks form several separate horizons in the Lower and Middle Devonian of the Lviv Basin, and in the Upper Devonian (Famennian) of the Lublin Basin. Their filtration properties relate to intergranular porosity, while the fracture space has subordinate significance. Carbonate rocks form thick saturated horizons in the Givetian in the Lviv Basin, and in the Eifelian, Givetian and Frasnian in the Lublin Basin. Their filtration properties are produced by fracture porosity. Sulphates and carbonate-sulphate rocks with fracture and cavern porosity play a role as reservoir horizons in the Middle Devonian of the Lublin Basin. The natural gas collected from the Upper Devonian of the Lublin Basin was generated mainly during low-temperature thermogenic processes, from Ordovician–Silurian Type-II kerogen. The gas from the Middle Devonian reservoirs of the Lviv Basin was produced from Ordovician–Silurian Type-II kerogen and partly from the Middle and Upper Devonian mixed Type-III/II kerogen with maturity from about 0.9 to 1.4%. Carbon dioxide was formed by both thermogenic and microbial processes. Molecular nitrogen was generated mainly through thermal transformation of organic matter and also from destruction of NH 4 -rich illite of the clayey facies of the Ordovician–Silurian strata

Stable isotope geochemistry of the nitrogen-rich gas from lower Cambrian shale in the Yangtze Gorges area, South China

The organic-rich marine shales from the lower Cambrian Niutitang formation in the Yangtze Gorges area are characterized by their high TOC values (0.54–5.13%), types I and II organic matter, and high Ro values (2.4%–2.6%). Geochemical parameters of 19 gas samples from the lower Cambrian shale formation from well ZD-1 were analyzed in this study. The gases are dominated by methane, with small amounts of ethane and no propane or butane. The δ13C(CH4) values range from −31.7‰ to −27.9‰, the δ13C(C2H6) values range from −35.2‰ to −33.4‰, and the δ2H(CH4) values range from −214‰ to −187‰. Furthermore, carbon isotopic compositions of the alkane gases from the lower Cambrian shale are characterized by δ13C1 > δ13C2; these results indicate that the gases are of thermogenic origin and are oil-derived. Moreover, methane with heavy carbon isotopic and light hydrogen isotopic values may be produced when water reacts with inorganic carbon. The isotopic reversal of alkane gases was probably due to destructive redox reactions at maximum burial resulting in Rayleigh-type fractionation and/or mixing by gases from the same source but at a different maturity. Nitrogen occurs in the analyzed gases at concentrations from 8.15 to 96.52%, and the δ15N(N2) values vary from 3.2 to 7.4‰. The δ15N(N2) values and high illite content suggest that nitrogen was mainly generated during thermal transformation of organic matter and/or from NH4-rich illites of the clayey facies of the lower Cambrian shale. Carbon dioxide concentrations vary from 1.13 to 4.96%, and the δ13C(CO2) values range from −8.9 to −13.6‰. This suggests that carbon dioxide was mainly generated during thermogenic processes of transformation of organic matter. Moreover, the major reason for the change in nitrogen and methane contents in the studied well (ZD-1) is probably due to the development of micro cracks in core samples with high contents of nitrogen. A high nitrogen content may be caused by the strong adsorption capacity of nitrogen, which leads to the retention of nitrogen and the diffusion of methane in shale.

Molecular and isotopic compositions and origin of natural gases from Cambrian and Carboniferous-Lower Permian reservoirs of the onshore Polish Baltic region

Natural gases from Middle Cambrian and Carboniferous-Lower Permian reservoirs of the onshore Polish Baltic region were studied for their molecular and stable isotope compositions. The following gas species were analysed: 12,13C in CH4, C2H6, C3H8, n-C4H10, i-C4H10 and CO2, 1,2H in CH4, 14,15N in N2, and stable isotopes of all noble gases. Due to significantly different geological settings and genetic types of source rocks of Eastern and Western Pomerania, the molecular and isotopic compositions of natural gases of these two regions exhibit distinct differences. Hydrocarbon gases associated with oil accumulated in the Middle Cambrian reservoir of Eastern Pomerania were generated during low-temperature thermogenic processes from a single source rock containing Type-II kerogen at one phase of petroleum generation. Non-associated hydrocarbon gases accumulated in the Carboniferous (Mississippian and Pennsylvanian)-Lower Permian (Rotliegend) reservoirs of Western Pomerania originated during at least two phases of gas generation by thermogenic processes from mainly Type-III kerogen and a small component of mixed Type-III/II kerogen. Noble gases are in general heavily enriched in radiogenic and nucleogenic isotopes such as 4He, 40Ar and 21Ne accumulated in the reservoirs. Weak contributions of mantle-derived He and Ne are observed. Radiogenic 4He/40Ar ratios are higher than the average production rate ratio of about 5 for radiogenic 4He/40Ar in crustal materials, which might have been caused by a selective supply of 4He that is lighter than 40Ar from crustal rocks, or (U + Th)/K ratio might be higher than the average in crustal block. Carbon dioxide from gases of both the Western and Eastern Pomerania were mainly generated during thermogenic processes of transformation of organic matter, although gases of Western Pomerania can contain an endogenic component. Molecular nitrogen from the Eastern Pomeranian natural gases was mainly generated during low-temperature thermal transformation of organic matter and derived from NH3 and NH4 of crustal fluid, whereas molecular nitrogen from Western Pomeranian natural gases contains a significant component from the destruction of organic matter at a higher maturity level which may have been caused by a high heat flux from the volcanic activity during late Pennsylvanian–early Rotliegend ages, and has a bigger component release from NH4-rich illites.

Origin of gaseous hydrocarbons, noble gases, carbon dioxide and nitrogen in Carboniferous and Permian strata of the distal part of the Polish Basin: Geological and isotopic approach

Sixteen natural gas samples collected from Pennsylvanian and Permian (Rotliegend and Zechstein Limestone) strata of the distal part of the Polish Basin in Wielkopolska and Lower Silesia were analysed for molecular composition and stable carbon isotope composition of hydrocarbons (CH4, C2H6, C3H8, n-C4H10 and i-C4H10) and CO2, stable hydrogen isotope composition of methane, stable nitrogen isotope composition of N2, and stable isotope composition of noble gases (He, Ne, Ar, Kr, and Xe). Thirteen of analysed hydrocarbon gases reveal complete [δ13C(CH4)>δ13C(C2H6)>δ13C(C3H8)] and partial inversed isotopic trends from methane to propane thus they have a very complicated generation, migration and accumulation history and range of their source rock horizons. Two source rock horizons occur NE from Wolsztyn Ridge. They contain mixed types III/II and II/III kerogens of Pennsylvanian age and Mississippian and/or Devonian age, respectively. One source rock horizon occurs SW from Wolsztyn Ridge. It contains type III and mixed type III/II kerogens of Pennsylvanian age. The kerogens in all source rock horizons generated gaseous hydrocarbons at two separate maturity stages: about 0.5 to 0.8% in vitrinite reflectance scale at the first maturity stage, and over 1.3% in vitrinite reflectance scale at the second maturity stage. High concentrations of He in analysed gases are mostly a product of α-decay of U and Th enriched in crustal materials. A small contribution of He and Ne of mantle origin to the gas reservoirs was inferred. Radiogenic 4He/40Ar ratios are higher than the average production rate ratio of about 5 for crustal materials, which might have been caused by a selective supply of lighter He through crustal rocks surrounding the gas reservoirs, or higher (U+Th)/K ratio than the crustal average. CO2 from analysed gases was mainly generated during thermogenic processes of transformation of organic matter, although some gases can contain components from endogenic processes and from thermal destruction of Zechstein Limestone and probably Precambrian carbonates. N2 was mainly generated during thermal transformation of organic matter and had a large component released from NH4-rich illites. Very high N2/40Ar for the gases might be caused by accelerated thermogenic production of N2 under the condition of high heat flux from volcanic activity at late Pennsylvanian and early Permian age. Deep-seated faults, mainly framing the Wolsztyn Ridge, perform important role in migration and mixed in different proportions of noble gases originated from upper mantle and from mineralisation by radioactive minerals their fault surfaces and occurrence of Pennsylvanian–Lower Permian volcanites in crust as well as hydrocarbon gases, CO2 and N2, also from thermal destruction of NH4-rich illites, from “gas generation kitchens” of source rock horizons to the traps.

Sources of natural gases in Middle Cambrian reservoirs in Polish and Lithuanian Baltic Basin as determined by stable isotopes and hydrous pyrolysis of Lower Palaeozoic source rocks

Origin of natural gases associated with oil and condensate accumulations within the Middle Cambrian sandstone reservoir of the Polish and Lithuanian Baltic Basin was characterised by means of molecular composition, stable carbon isotopes of methane, ethane, propane, butanes, pentanes and carbon dioxide, stable hydrogen isotopes of methane and stable nitrogen isotopes of gaseous nitrogen. Generated gas from potential Upper Cambrian, Tremadocian, and Llandovery source rocks by hydrous pyrolysis at 330°C and 355°C for 72h was used to characterise thermogenic gas to evaluate correlation parameters based on molecular composition and stable isotopes. The pyrolysis conditions represent gas generation during oil generation, which appears to be the conditions represented by the natural gas accumulations and their low GORs (gas:oil ratios). The dryness of the pyrolysis and natural hydrocarbon compositions compare well, but do not provide a means of distinguishing the contributions of each source rock to the natural gas accumulations. The average δ13C value of the natural methane is 6.9‰ depleted in 13C compared to methane generated in the hydrous pyrolysis experiments. This difference is less for ethane and essentially nonexistent for propane, butanes, and pentanes. Tentatively, this diminishing difference with increasing carbon number is attributed to kinetic effects resulting from higher experimental temperatures. Although the δ13C values of methane and ethane from the hydrous pyrolysis experiments are not useful in direct correlations with natural gas accumulations, δ13C of propane, butanes, and pentanes is useful, and indicates that the Upper Cambrian and Tremadocian source rocks are the main contributors and that the Llandovery source rocks are not significant contributors to the Polish and Lithuanian Baltic natural gases. Polish natural gases with relatively higher methane and ethane are attributed to the mixing of drier, more mature gases from deeper parts of the basin to the west. Carbon dioxide of natural gases was generated during thermogenic processes and gaseous nitrogen was generated from NH4-rich illites of the clayey facies and from thermal transformation of organic matter of the Lower Palaeozoic strata. Hydrous pyrolysis gases have higher concentrations of CO2, H2S and H2 than the natural gases. This difference is attributed to reduction or loss of these highly reactive and soluble gases during migration and entrapment of the natural gases. Although CO2 concentrations between pyrolysis and natural gases are different, the δ13C values of the former fall within the range of the latter.

Thermal transformation of organic matter in coal waste from Rymer Cones (Upper Silesian Coal Basin, Poland)

Abstract Coal wastes produced at various stages of coal mining, washing and deposition on dumps are a source of many pollutants. In some cases, the dumped coal waste undergoes self-heating and self-combustion processes that reflect the properties of the organic matter present (maceral composition and rank) and the history of heating (rate, time and temperature of heating). In the examination of the coal wastes from the Rymer Cones dump, petrographic- and gas chromatography-mass spectrometry (GC-MS) techniques were used to provide different sets of complementary data. Unaltered- and variably-altered macerals (mostly vitrinite) characterise the investigated material. Vitrinite of elevated reflectance and massive coke particles indicate that the rate of heating was low and that the availability of air was very limited; heating took place under pyrolytic conditions. Irregular cracks in particles probably also resulted from slow heating. The temperature of the heating processes, dynamically changing in time and place throughout the dump, led to chemical changes in organic matter such as the formation of phenols and their derivatives, and alteration in distributions of n-alkanes, hopanes and moretanes and polycylic aromatic hydrocarbons (PAHs) occurring in pyrolysates. Some of these compounds formed as a result of the thermal destruction of liptinite and vitrinite macerals at various temperatures and migrated from within the dump. The changes that occurred within the dump are also reflected in values of geochemical parameters based on the same compounds, such as CPI, Ts/(Ts + Tm), MNR, DNR, TNR-1, TNR-2. Lighter compounds were probably released into the atmosphere and others, especially phenols that are easily soluble in water and PAHs, were most probably leached into deeper parts of the dump and even into underground waters since they are absent in some samples or significantly decreased in concentration. These processes probably still continue — it is this fact that creates a potential hazard to the environment.

Composition and origin of natural gases accumulated in the Polish and Ukrainian parts of the Carpathian region: Gaseous hydrocarbons, noble gases, carbon dioxide and nitrogen

Ten natural gas samples associated and non-associated with oil in the Polish and Ukrainian Flysch Carpathians and Mesozoic Basement of the Carpathian Foredeep were analysed for molecular and stable isotope compositions as follows: 12, 13C in CH 4, C 2H 6, C 3H 8, and CO 2, 1, 2H in CH 4, 14, 15N in N 2, and 3, 4He, 20, 21, 22Ne, 36, 38, 40Ar, 84Kr and 132Xe in noble gases. The gaseous hydrocarbons both in the Silesian Unit of the Outer Flysch Carpathians and Mesozoic Basement are generally genetically related to thermogenic processes and occasionally to microbial carbon dioxide reduction. These gases were mainly generated from mixed type II/III kerogen during middle stage of the low-temperature thermogenic processes. Gaseous hydrocarbons from Starunia in the Boryslav-Pokuttya Unit were generated from type II kerogen during middle stage of the low-temperature thermogenic processes. He is generally of crustal origin with more than 99.2% of radiogenic 4He, but appreciable amount of 3He is probably derived from the upper mantle. The 3He might have been derived from the Pieniny Klippen Belt deep-seated fault system or Neogene and Pleistocene andesitic and basaltic volcanism occurred in the eastern Carpathian area. Nucleogenic 21Ne and 22Ne were analysed in all the samples. The nucleogenic 21Ne shows good correlation with radiogenic 4He with the production ratio of 4He/ 21Ne = (1–3) × 10 7 in the crust. These isotopic values indicate a common source for these gases, where both the nuclear reactions of α-decay and ( α, n) are occurring. Concentrations of radiogenic 4He and 40Ar and excess 21Ne in the samples from the Mesozoic Basement are generally higher and more scattered compared with those in the Silesian Unit. The larger concentrations of radiogenic and nucleogenic isotopes in the natural gases from the Mesozoic Basement is probably related to older geological formations than younger formations of the Silesian Unit. Carbon dioxide was generally generated during the thermal transformation of organic matter, and occasionally during microbial processes. Nitrogen was mainly generated during thermal transformation of organic matter and also originated from atmosphere. A least part of carbon dioxide and nitrogen may have been produced in crust.