Open System Non-isothermal Pyrolysis Research Articles

A pyrolytic study of the speciation and isotopic composition of nitrogen in carboniferous shales of the North German Basin

Thick layers of Palaeozoic shales are considered the potential sources of N 2 in natural gas reservoirs of the North German Basin. The nitrogen geochemistry of shale samples from five wells in northern Germany has been investigated using elemental analysis, stable isotope mass spectrometry and open system non-isothermal pyrolysis (temperature programmed pyrolysis). A combination of pyrolysis and on-line isotopic analysis of the liberated N 2 was used to identify variations in the isotopic composition of nitrogen-containing precursor species in the shales. Proportions of organic and inorganic nitrogen were assessed via pyrolysis of bulk samples and the corresponding demineralized kerogen concentrates. Total nitrogen content of the samples ranged between 640 ppm and 2350 ppm (0.64 and 2.35 mg N/g rock). Pyrograms of Namurian A and B shales indicated a clear facies trend from marine sediments to paralic and terrestrial facies. The isotopic composition of the liberated N 2 varied with temperature. The isotope trends imply the presence of several distinct precursor species with different isotope signatures.

Liberation of volatiles from Greek lignites during open system non-isothermal pyrolysis

Open system non-isothermal (programmed) pyrolysis with on line quantitative gas chromatographic analysis of pyrolysis gases (methane, carbon dioxide, carbon monoxide and molecular nitrogen) was performed on a series of Greek lignite samples. The investigation was aimed at exploring variations in the chemical properties of the samples and correlating them with petrographic data. For reference purposes one lignite sample from NW Germany was studied using the same procedure. The pyrograms of the four gases are sensitive indicators reflecting the chemical composition of the lignites. They represent unique fingerprints and document a greater variability in chemical composition than suggested from the petrographic data and proximate analysis.

CH 4/N 2 Ratio as a Potential Alternative Geochemical Tool for Prediction of Thermal Maturity of Natural Gas in Tarim Basin

In this context, the bulk ratio of CH 4/N 2 is examined as a potential alternative geochemical parameter for the assessment of thermal maturity of natural gas and compared to other previously published data. Open-system non-isothermal pyrolysis of low-mature coal from the Manjiaer sag, Tarim basin, yielded generation curves for methane and nitrogen. Analysis of the change of vitrinite reflectance indicates a two-stage process of thermal maturation with increasing temperatures. The relationship between R o and pyrolysis temperature could be expressed by the following equations: Stage I: R o = 0.0014 T + 0.109, r = 0.9931( R o < 0.6%); Stage II: R o = 0.0067 T −1.5855, r = 0.9996 ( R o > 0.6%). A kinetic interpretation of the characteristics of nitrogen and methane generation in humic coal during laboratory pyrolysis indicates that the bulk ratios of methane and nitrogen as thermal maturity parameters may be applied to assess the maturity of gas-sources. Thus, the maturity of the source rocks of natural gases in the Tarim basin was expressed in terms of CH 4/N 2 ratios and compared with other geochemical natural gas parameters, such as stable isotopes. The predicted results were found to be consistent with the published data.

Investigation of the pyrolytic liberation of molecular nitrogen from Palaeozoic sedimentary rocks

Open-system non-isothermal pyrolysis up to 1,200°C in combination with elemental analysis was used to study the thermal liberation of molecular nitrogen (N2) from sedimentary rocks and kerogen concentrates of Palaeozoic age from the Central European Basin system and an Eocene shale (Liaohe Basin, China) with a high content (36%) of ammonium feldspar (buddingtonite). The N/Corg (atomic) ratios of the kerogen concentrates ranged from 0.005 to 0.014, which represents the range commonly observed for coals. Bulk N/Corg ratios of the Palaeozoic shales extended from 0.035 to 0.108, indicating the presence of significant amounts of inorganic nitrogen. Namurian A and A-B (CnA; CnA-B) samples typically exhibited the earliest onset of N2 generation with intense, characteristic peaks around 600°C. N2 liberation from the buddingtonite-rich sample occurred at higher temperatures, with a broad peak around 700°C. Pyrograms of the kerogen concentrates showed no or strongly reduced N2 generation in the 500–700°C range. On-line isotope-specific analysis of the pyrolytically liberated N2 on one sample revealed a variability of ∼10‰ in the δ15N values and a steady increase in δ15N with temperature during the main phase of N2 generation.

On-line pyrolysis-GC-IRMS: isotope fractionation of thermally generated gases from coals

The isotopic composition of reservoir gases is frequently used for source rock to gas correlations. The prime control on the isotopic signature of gas results from kinetic isotope fractionation during thermal gas generation. A new on-line pyrolysis-GC-IRMS system has been developed as an analytical tool to study the kinetic isotope fractionation during thermal gas generation from sedimentary organic matter. The method is based on open-system non-isothermal pyrolysis in the temperature range from 100 to 1100°C and allows simultaneous monitoring of the isotopic composition of seven individual pyrolysis product (methane, ethane, ethene, propane, propane, carbon monoxide and carbon dioxide) at a high sampling frequency. Due to the high data density achieved by this procedure a detailed reaction kinetic interpretation of the pyrolysis curves in terms not only of compositional but also isotope specific reaction kinetics is feasible. This method and the data presented encourage both the re-evaluation of existing concepts for source-rock to gas correlations and also offer new insights into controls on isotope fractionation during thermal gas generation. Current results indicate a high variability of the isotopic composition of the seven pyrolysis products. Although a general trend of enrichment in the 13C species with increasing pyrolysis temperature is observed, characteristic reversals of this isotopic trend are commonly occurring for methane, CO, and CO 2. These variations reflect differences in the isotopic composition of the precursor structures, which are progressively decomposed during pyrolysis. The analytical data obtained from the approach presented here open up the perspective of developing new kinetic fractionation models taking into account both the isotopic variability of precursor structures and their thermal stability.

Reaction Kinetics of Stable Carbon Isotopes in Natural GasInsights from Dry, Open System Pyrolysis Experiments

Open system nonisothermal pyrolysis with on-line compound-specific 13C/12C stable-isotope analysis (Py-GC/IRMS) has been performed on three carbonaceous sediments from NW Germany (Carboniferous, Westphalian coal, HI = 286 mgHC/gTOC, Ro = 0.72%), West Siberia (Cretaceous, Cenomanian shale, HI = 192 mgHC/gTOC, Ro = 0.43%), and Malaysia (Tertiary, Miocene coal, HI = 190 mgHC/gTOC, Ro = 0.36%). The study was focused on the generation of methane, ethane, and propane + propene. Measured δ13C-values of pyrolytically generated light hydrocarbons were in the range of δ13C-values commonly observed in thermogenic natural gas (−20 to − 40‰, PDB). While the isotopic composition of the pyrolysis products showed a general enrichment in 13C-species with increasing temperature, the isotopic trends of methane displayed characteristic structures involving reversals in certain temperature intervals. On the basis of the experimental data, reaction kinetic parameters have been derived for each isotopic species of the hydrocarb...

3D-modelling of thermal history and simulation of methane and nitrogen migration along the Northeast German seismic DEKORP profile 9601

The Northeast German Basin (NEGB) is generally regarded as a long-lived intracontinental sedimentary basin. Deeply buried Carboniferous rocks are the main source rocks for hydrocarbon gases and nitrogen in the basin. For the northern part of the NEGB the thermal and burial history was reconstructed and simulated. Open system non-isothermal pyrolysis was used to determine the generation potential of methane and nitrogen and the corresponding kinetic parameters. These experimental data are used in a kinetic model to estimate timing and efficiency of gas generation in the NEGB and to assess, in a subsequent step, the gas migration pathways. Pyrolysis experiments of overmature Carboniferous samples and their corresponding kerogen concentrates indicate that a considerable amount of nitrogen comes from the inorganic matrix, probably ammonium illite. The simulation results reveal that the main methane generation took place during the rapid subsidence of Upper Rotliegend to Middle Triassic sediments. A residual gas potential exists only in the northern parts of the basin.

On-line couplmg of open-system nonisothermal pyrolysis and GC/IRMS: A new technique to investigate generation and accumulation history of natural gas

On-line couplmg of open-system nonisothermal pyrolysis and GC/IRMS: A new technique to investigate generation and accumulation history of natural gas

Compositional information for kinetic modelling and petroleum type prediction

The process of petroleum generation can be described in terms of timing and quantity by kinetic modelling. Compositional changes which occur during maturation are usually not taken into account in these models, despite the fact that they play an important role in defining physical behaviour of the petroleum under changing subsurface conditions. With this in mind, both open and closed system pyrolysis methods were applied to a set of immature Posidonia Shale samples from the Lower Saxony Basin (NW Germany) for studying both qualitative and quantitative aspects of the petroleum generation process. With the open system non-isothermal pyrolysis method, discrete distributions of activation energies in the range of 47–53 kcal/mol and one single frequency factor were determined. A maturity sequence was established by pyrolysing aliquots of immature Posidonia Shale samples under closed system conditions for various times and temperatures. The compositional changes and the kinetics of formation of single compounds and groups in the C 1–C 35 range were then studied quantitatively using gas chromatography. The sequence was characterised by a progressive increase in both gas/oil ratio (GOR) and paraffinicity. There was only minor variation of the chain length distribution of n-alkanes, indicating a limited pool of precursors in the Posidonia Shale kerogen. Different kinds of single reaction models were used to determine the kinetic parameters for n-alkane generation. A satisfactory fit to the experimental data could not be obtained with first-order kinetics. A good fit could be made using a kinetic model of autocatalytic reactions.