Kerogen of Toarcian shales of the Paris Basin. A study of its maturation by flash pyrolysis techniques

A set of 14 samples—both extracted and unextracted from the Toarcian of the Paris Basin have been investigated using Curie-point pyrolysis-mass spectrometry and Curie-point pyrolysis gas chromatography mass spectrometry. The relative amount of n-alkenes and n-alkanes in the pyrolyzates increases with increasing maximum burial depth of the samples. Comparison of the pyrolysis data of extracted and unextracted samples shows that generation of hydrocarbons from the kerogen starts at a maximum burial depth of ~ 1000m. The increase of pristane and phytane in the extracts of the deeper samples is correlated with the gradual decrease of the characteristic pyrolysis product prist-1-ene. Three samples yield pyrolyzates with high relative amounts of aromatic compounds. This phenomenon probably reflects a different type of contributing organic matter and/or a different environment of sedimentation.     

Organic geochemical analysis of sedimentary organic matter associated with uranium

Samples of sedimentary organic matter from several geologic environments and ages which are enriched in uranium (56 ppm to 12%) have been characterized. The three analytical techniqyes used to study the samples were Rock-Eval pyrolysis, pyrolysis-gas chromatography-mass spectrometry, and solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy. In samples with low uranium content, the pyrolysis-gas chromatography products contain oxygenated functional groups (as hydroxyl) and molecules with both aliphatic and aromatic carbon atoms. These samples with low uranium content give measurable Rock-Eval hydrocarbon and organic-CO₂ yields, and C-13 NMR values of > 30% aliphatic carbon. In contrast, uranium-rich samples have few hydrocarbon pyrolysis products, increased Rock-Eval organic-CO₂ contents and > 70% aromatic carbon contents from C-13 NMR. The increase in aromaticity and decrease in hydrocarbon pyrolysis yield are related to the amount of uranium and the age of the uranium minerals, which correspond to the degree of radiation damage. The three analytical techniques give complementary results. Increase in Rock-Eval organic-CO₂ yield correlates with uranium content for samples from the Grants uranium region. Calculations show that the amount of organic-CO₂ corresponds to the quantity of uranium chemically reduced by the organic matter for the Grants uranium region samples.     

Petrographic and geochemical characteristics of organic matter associated with stream sediments in Trail area British Columbia,Canada

Fifty-six samples of stream sediments from 12 creeks in the vicinity of Trail, British Columbia, Canada were examined to determine their origin, characterize their organic matter and their relation to natural/geogenic and anthropogenic sources. The samples were initially screened by Rock-Eval® 6 pyrolysis for their TOC, HI, and OI contents and then examined by both reflected (polarized) and fluorescent light microscopy. It was found that organic matter in stream sediments is mostly from natural/biological sources from local vegetation, such as woody tissue, suberin, spores, and pollen, as well as altered natural/biological input from char formed due to forest fires. Anthropogenic organic matter, mostly coke particles, was also found in the stream sediments. The coke particles have anisotropic properties with medium grained texture formed from medium volatile bituminous coal. The occurrence of coke particles is limited to Ryan Creek located close to an area were some small gold, nickel, and lead smelting operations previously occurred. There is no evidence to indicate that the coke particles found in the creek are emitted from the lead and zinc smelter currently in operation in the area. There are no coal-bearing strata in the area that may have a direct input of coal fragments in any of the creeks.     

Investigation of catalytic effects of indigenous minerals in the pyrolysis of Aleksinac oil shale organic matter

The catalytic effect of indigenous minerals in the pyrolysis of Aleksinac (Yugoslavia) oil shale was studied in this paper. The substrates were prepared by gradual removal of the mineral constituents (carbonates, silicates, pyrite) and the free and bound bitumens. The substrates were analyzed by chemical methods, X-ray diffraction, porosimetry, thermal analysis, ¹³C NMR, and standard ASTM Micro Activity Test (MAT) designed for the investigation of cracking catalysts. The liquid pyrolysis products were analyzed by organic geochemical techniques as well. Based on the yields of gaseous and liquid products and the coke, conversion degrees, GC analyses (MAT parameters) and weight losses (TG parameter), the catalytic effect of indigenous mineral components in the pyrolysis of Aleksinac oil shale organic matter was found to be very low. The results suggested that principal organic matter changes should be attributed to thermal rather than to catalytic cracking.     

Source Rock Characterization and Petroleum Systems in North Ghadames Basin,Southern Tunisia

This paper presents geochemical analysis of drilled cutting samples from the OMZ‐2 oil well located in southern Tunisia. A total of 35 drill‐cutting samples were analyzed for Rock‐Eval pyrolysis, total organic carbon (TOC), bitumens extraction and liquid chromatography. Most of the Ordovician, Silurian and Triassic samples contained high TOC contents, ranging from 1.00 to 4.75% with an average value of 2.07%. The amount of hydrocarbon yield (pyrolysable hydrocarbon: S2b) expelled during pyrolysis indicates a good generative potential of the source rocks. The plot of TOC versus S2b, indicates a good to very good generative potential for organic matter in the Ordovician, Silurian and Lower Triassic. However, the Upper Triassic and the Lower Jurassic samples indicate fair to good generative potential. From the Vankrevelen diagram, the organic matter in the Ordovician, Silurian and Lower Triassic samples is mainly of type II kerogen and the organic matter from the Upper Triassic and the Lower Jurassic is dominantly type III kerogen with minor contributions from Type I. The thermal maturity of the organic matter in the analyzed samples is also evaluated based on the T_max of the S2b peak. The Ordovician and Lower Silurian formations are thermally matured. The Upper Silurian and Triassic deposits are early matured to matured. However, Jurassic formations are low in thermal maturity. The total bitumen extracts increase with depth from the interval 1800–3000 m. This enrichment indicates that the trapping in situ in the source rocks and relatively short distance vertical migration can be envisaged in the overlying reservoirs. During the vertical migration from source rocks to the reservoirs, these hydrocarbons are probably affected by natural choromatography and in lower proportion by biodegradation.     

Alkene transformations catalysed by mineral matter during oil shale pyrolysis

The effects of mineral matter on the pyrolysis behavior of an Australian aliphatic oil shale (Rundle, aromaticity = 0.21) have been studied. Besides confirming previous reports that mineral matter in highly aliphatic shales reduces the yield of oil from pyrolysis, the results clearly show that some mineral matter components such as montmorillonites and poorly ordered aluminosilicates can reduce the ratio of 1-alkenes to internal alkenes in oils. Isomerization is dependent on the type of aluminium coordination in the mineral matter and the tetrahedral aluminium is most efficient at altering alkene ratios. Although there is no evidence that mineral matter operates through a carbocationic mechanism to reduce the oil yield, the results strongly suggest that such a mechanism operates during alkene isomerization.     

Understanding compost effects on water availability in a degraded sandy soil of Patagonia

Disturbances have the potential to reduce soil water and nutrient retention capacity by decreasing soil organic matter (SOM), which is particularly true for sandy soils characterized by an inherent low capacity to retain nutrients and water. To restore degraded areas, several works have shown positive effects of organic matter inputs on soil properties and plant growth. Despite these promising results, it is still unclear how organic matter inputs and plant growth modify the balance between soil nutrient and water supply. The objectives of the present work were (1) to evaluate the effects of biosolids compost and municipal compost addition on plant available water (PAW), soil moisture and soil temperature in a burned sandy soil of NW Patagonia (Argentina), and (2) to relate PAW and soil moisture with bulk density, soil organic carbon, nutrient availability (inorganic and potential mineralized nitrogen (N), extractable phosphorous) and aboveground phytomass. An experiment with excised vegetation and watering was also conducted. Compost application increased SOM, but it was insufficient to increase PAW. The increase in potential mineralized N in the amended soils indicated that during moist periods (and adequate temperatures), N uptake was increased, enhancing plant growth. As a consequence, higher plant water consumption in amended treatments resulted in lower soil moisture than in non-amended plots during the vegetative growth period that coincides with decreasing precipitation. Results indicate that a relatively high dose of compost (40 Mg ha^?1) applied to a sandy soil, contributed to increase nutrient availability and consequently, aboveground phytomass and water consumption.     

Investigating the variations in carbon and nitrogen isotopes in carbonaceous chondrites

The carbonaceous chondrites contain significant amounts of carbon- and nitrogen-bearing components, the most abundant of which is organic matter. Stepped combustion data of whole rock and HF/HCl residues of carbonaceous chondrites reveal that the organic material can be subdivided operationally into three components: (1) free organic matter (FOM), which is readily extractable from whole-rock meteorites and is enriched in ¹³C and ¹⁵N; (2) labile organic matter (LOM), which has a macromolecular structure but is liberated by hydrous pyrolysis; LOM is the parent structure for some FOM and is also enriched in ¹³C and ¹⁵N; and (3) refractory organic matter (ROM), which is also macromolecular but is virtually unaffected by hydrous pyrolysis and is relatively depleted in ¹³C and ¹⁵N. The macromolecular entities (LOM and ROM) are by far the most abundant organic components present, and as such, the relative abundances of the ¹³C- and ¹⁵N-enriched LOM and the ¹³C- and ¹⁵N-depleted ROM will have a major influence on the overall isotopic composition of the whole-rock meteorite. Laboratory experiments designed to simulate the effects of parent body aqueous alteration indicate that this form of processing removes LOM from the macromolecular material, allowing ROM to exert a stronger influence on the overall isotopic compositions. Hence, aqueous alteration of macromolecular materials on the meteorite parent body may have a significant control on the stable isotopic compositions of whole-rock carbonaceous chondrites. The enstatite chondrites are also carbon rich but have been subjected to high levels of thermal metamorphism on their parent body. Stepped combustion data of HF/HCl residues of enstatite chondrites indicate, that if they and carbonaceous chondrites inherited a common organic progenitor, metamorphism under reducing conditions appears to incorporate and preserve some of the ¹³C enrichments in LOM during graphitisation. However, when metamorphism is at its most extreme, the ¹⁵N enrichments in LOM are lost.     

Potential source rocks, organic geochemistry and thermal maturation in the southern depocenter (Kipourio–Grevena) of the Mesohellenic Basin, central Greece

The study area is the southern depocenter (depth > 4200 m) of the Mesohellenic Basin which extends between Kipourio and Grevena, central Greece. The Mesohellenic Basin is a Middle-Tertiary intramontane basin developed within the Hellenide orogen. Previous studies have focused on the depositional environments, configuration and hydrocarbon potential of the basin. In this paper we present additional geochemical and petrographic data from outcrop samples of the basin's southern depocenter, which is considered the most promising area, in terms of hydrocarbon prospectivity. A total number of thirty six samples were analysed: Rock-Eval pyrolysis, maceral analysis, vitrinite reflectance and thermal alteration index, bitumens extraction, liquid chromatography, and GC-MS. The samples were collected from deltaic deposits and submarine fan sediments of Late Eocene to Late Oligocene age. The TOC values of the analysed samples range between rich and very rich and the organic matter consists mainly of type III kerogen and the organic matter consider to be predominately gas prone. The thermal maturity assessed from T_max and vitrinite reflectance shows an immature stage of the organic matter along with the presence of layers having reached the very early mature stage. Vitrinite reflectance measurements and maturity calculations (applying the Lopatin modeling), reveal that the lower part of the depocenter sediments falls within the ‘oil window’. The extractable organic matter (EOM) (mg bitumens/g TOC) indicate the existence of samples (from deltaic deposits) with high ratio of transformation (EOM) (> 100 mg bitumen/g TOC). The GC and GC-MS analyses of the biomarkers indicate mainly the occurrence of terrestrial organic matter reflecting oxidizing conditions and both immature and very early mature stages. The results of the Rock-Eval pyrolysis and the distribution of the isoprenoids support the assumption of the input of an organic matter mixture.     

海相碳酸盐岩中矿物结合有机质的组成及成烃演化

对高成熟程度的碳酸盐岩有机质进行了地球化学研究,发现在可溶有机质与干酪根之间存在着成熟度上的差异,这种差异是矿物对沥青组份的保护作用所致.矿物结合有机质无论在组成还是在分布上都与游离态有机质有较大不同,随着成熟度的增加,由于结合态有机质的释放,这种不同逐渐消失,研究表明,矿物结合有机质的释放约在过成熟阶段早期,其量可达几百个ppm.因而在碳酸盐岩地层中,除了干酷根成油气外,在高成熟区亦可能存在着由矿物结合有机质形成的“高温”石油.     

Analysis of organic matter by flash pyrolysis-gas chromatography–mass spectrometry in the presence of Na-smectite: When clay minerals lead to identical molecular signature

Different studies have already pointed out the influence of clays during the analysis of pure organic compounds (especially alkanols, alkanoic acids) as well as macromolecules (humic acids) by flash pyrolysis-gas chromatography–mass spectrometry (PyGC–MS). Especially, the occurrence of clay minerals favors the generation of aromatic units such as alkylbenzenes and polycyclic aromatic hydrocarbons. So as to better identify the nature of the organic compounds which are sensitive to the presence of clays during flash pyrolysis, a humic acid mixed in variable proportions of a Na-homoionic clay was tested. The smectite/humic acid mixtures containing from 10% to 100% humic acid allowed us to identify the progressive disappearance or appearance of specific compounds after PyGC–MS.n-Alk-1-enes disappear when the clay proportion is higher than 67%. For higher contents of Na-smectite, n-alkanes become less and less abundant with a preferential consumption of high molecular weight n-alkanes, whereas the aromatic hydrocarbon proportion increases. Moreover, the distribution of each aromatic hydrocarbon family (alkylbenzenes and alkylnaphthalenes) has been investigated. The pyrogram of pure humic acid exhibits a specific distribution of alkylbenzenes and alkylnaphthalenes reflecting the structure of the organic macromolecule. With the increase in clay proportion, these distributions are modified and lead to other distributions with a preferential predominance of thermally stable isomers.Pyrograms of humic acid and undecanoic acid in the presence of 90% of Na-smectite are similar, especially concerning alkylbenzene and alkylnaphthalene distributions. Therefore, clays (Na-smectite in our experiments) in high proportion modify initial organic products by recombination reactions and lead to the generation of new compounds of very similar distribution, whatever the nature of the initial organic matter. Such results underline the very important catalytic properties of clay minerals on functionalized organic matter during flash pyrolysis.     

泥岩有水热解产生低分子量有机酸实验研究

直接采用泥岩岩屑进行有水热解,测定实验后水溶液中几种常见低分子量有机酸.结果表明,在实验的水溶液中检测到了丰富的低分子量有机酸,组成上主要为一元羧酸,其中又以乙酸占优势.讨论了不同热解条件对有机酸产率以及组成的影响.实验结果表明,有机酸总量随加热温度和时间增加而增加,并且溶液中不同有机酸相对组成也发生变化.当温度高于1...     

Effect of a dolerite intrusion on triterpane stereochemistry and kerogen in Rundle oil shale,Australia

Stereochemical changes of triterpanes present in extracts from an immature oil shale sequence intruded by a 3-m dolerite sill have been studied by gas chromatography-mass spectrometry (GC-MS). The steric configuration of the hopanes was observed to change from one dominated by the thermally less stable 17β(H), 21β(H) configuration at some distance from the intrusion, to one dominated by the thermally more stable 17α(H), 21β(H) and 17β(H), 21α(H) configurating in the immediate vicinity of the intrusion. In addition, severe alteration of the kerogen appeared to have taken place as a result of the contact metamorphism, and high concentrations of extractable organic matter were observed below the intrusion. Characterization of the kerogens by Curie-point pyrolysis has enabled the effects of the intrusion on the shales to be monitored.     

Organic geochemistry of Deep Sea Drilling Project sediments from the Gulf of Calofornia—hydrothermal effects on unconsolidated diatom ooze

The effects of intrusive thermal stress have been studied on a number of Pleistocene sediment samples obtained from Leg 64 of the DSDP-IPOD program in the Gulf of California. Samples were selected from Sites 477, 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions. For comparison purposes, samples from Sites 474 and 479 were selected as representative of unaltered material.The GC and GC-MS data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher-plant detritus. Samples from sill proximities were found to contain thermally-derived distillates and those adjacent to sills contained essentially no lipids. Curie point pyrolysis combined with GC and GC-MS was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin. Pyrograms of the altered kerogens were much less complex than the unaltered samples, reflecting the thermal effects. The kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated, wet sediments resulted in in situ pyrolysis of the organic matter.Examination of the kerogens by ESR showed that spin density and line width pass through a maximum during the course of alteration but ESR g-values show no correlation with maturity. Stable carbon isotope (δ¹³C) values of kerogens decrease by 1–1.5‰ near the sills at Sites 477 and 481 and the atomic N/C decreases slightly with proximity to a smaller sill at Site 478. Differences in maturation behavior between Site 477 and 481 and Site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of Guaymas Basin protokerogen.     

Hydrous pyrolysis of a Type III source: fractionation effects during primary migration in natural and artificially matured samples

A core from the Cambay Shale Formation of the Cambay Basin, containing immature Type III organic matter, was pyrolysed at 300°C for different durations of time to different maturation levels. Fractionation effects were studied employing a three-step extraction technique after removal of the expelled pyrolysate. The extractable organic matter (EOM) obtained on extraction of the whole core is assumed to be that present in open pores, while that obtained on finely crushing the sample is assumed to be that present in closed pores. The EOM obtained from 1 cm chips is termed EOM from semi-open pores. The gross composition of the pyrolysates expelled during pyrolysis is not similar to the oils reservoired in the area, and there is no significant fractionation observed between expelled pyrolysates and unexpelled EOM. Our study indicates movement of fluids between closed, semi-open and open pores. In both systems, there is a higher concentration of EOM in open pores than in semi-open and closed pores, and the fraction of EOM in open pores is much greater in the artificial system than in the natural system. Fractionation effects on n-alkane and isoprenoid hydrocarbon-based parameters were also studied. n-Alkenes are present in semi-open and closed pores of the immature core and in the core after it was pyrolysed to 300°C for 6 and 48 h, but are absent in the open pores. n-Alkenes are present in closed pores in the naturally matured core. Presence of n-alkenes in the pyrolysates expelled during the 6 and 48 h experiments, but their absence in the open pores of the core, indicates that expulsion also occurs through temporary microfractures during laboratory pyrolysis, whereas in the natural system expulsion from closed pores seems to be only via semi-open and open pores.     

Organic geochemical evidences of early-diagenetic oxidation of the terrestrial organic matter during the Triassic arid and semi arid climatic conditions

The molecular character of organic matter (OM) present in Triassic clays of the Upper Silesia Basin and NW border of the Holy Cross Mountains was determined using GC–MS analysis. Oxidation processes were the major cause of the main changes of extractable OM molecular composition during sedimentation and early diagenesis of the Triassic clays. They resulted in a very significant decrease in the OM content of the clays and transformation of n-alkanes, triterpanes and steranes. Despite the changes in biomarker composition resulting from the disappearance of unsaturated and ββ hopanes and dominance of αβ and βα hopanes as well as preponderance of αββ over ααα steranes, the aromatic ketones were identified. Such PACs as benzophenone, fluorenone, cyclopenta(def)phenanthrenone, antracenone and benzanthrone were among the compounds identified in the red clays. These commonly originate during oxidation of sedimentary organic matter. Moreover, the aromatic fraction is characterized by the presence of phenyl derivatives (phenylnaphthalenes, terphenyls, phenyldibenzofurans and phenylphenanthrenes) that are also products of the abiotic oxidation of organic matter. Periods of terrestrial sedimentation have been interrupted by long phases of OM weathering and oxidation during arid conditions, and OM might only have survived without significant oxidation changes when the sedimentation was fast and/or long-lasting.     

粘土矿物对有机质生烃的催化作用

烃源岩的有机质主要以有机粘土复合体的形式存在。有机质生烃是一种有机粘土化学反应。反应过程中,有机质与粘土之间存在质子和电子迁移,粘土通过对水分子的吸附和离解为有机质加氢裂解提供H+,而有机质生成的有机酸激活了粘土的催化活性,也为蒙皂石伊利石化反应创造了条件。烃源岩不同粘土矿物的选择性催化特征是影响油气组成的最重要因素。粘土的催化活性大小和发育时间是决定烃源岩生烃潜力大小的因素。由于烃源岩在蒙皂石伊利石化阶段具有最大的催化活性,而且与有机质生烃反应同步,因此富含伊$蒙混合层的烃源岩是世界含油气盆地的最有利烃源岩。不同地质时期的烃类地质储量与烃源岩膨胀性粘土的丰度有密切关系。     

Selective loss of carbohydrates from plant remains during coalification

Fossil leaves ofOleinites willsii, Banksieaephyllum angustum, associated organic matter and rhizomes ofGleichenia sp. isolated from Yallourn brown coal deposits, Latrobe Valley, Victoria, Australia and their living relatives have been analysed by high-resolution solid-state¹³C nuclear magnetic resonance spectroscopy, infrared spectroscopy and pyrolysis—gas chromatography—mass spectrometry. The fossil leaves and rhizomes retain carbohydrates and, on a carbon basis, the amounts of carbohydrates in the fossil rhizomes and their living relatives appear to be similar. On the other hand, the amount of carbohydrates in the fossil leaves is substantially less than in the living relatives. The organic matter found intimately associated with the fossil leaves is quite different in structure from the fossil leaves themselves and bears a closer resemblance to humic acids and the smallest (<75μm) fractions of Yallourn brown coal. Since the fossil leaves are found in stratified beds, interfolded with associated organic matter, it is suggested that during coalification the leaves and associated organic matter undergo independent transformations and are brought together by water transport.     

The alteration of organic matter in response to ionising irradiation: Chemical trends and implications for extraterrestrial sample analysis

Ionising radiation is an energy source capable of generating and altering complex organic matter. A full understanding of the radiolytic formation and evolution of organic matter is essential to appreciate the budget of organic chemicals that exist in cometary and interstellar ices, carbonaceous meteorites, and to understand the results of analyses of irradiated extraterrestrial organic matter, such as that in cometary nuclei. The effects of ionising radiation on a set of 10 naturally occurring, terrestrial organic assemblages have been revealed by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), carbon isotopic analysis, and stepped combustion-isotope ratio mass spectrometry (SC-IRMS). Progressive radiolytic alteration of biogenic complex-hydrocarbon mixtures induces a decrease in the average size and extent of alkylation of polyaromatic hydrocarbons (PAH) and an increase in the abundance of oxygen-containing compounds, as indicated by Py-GC-MS, and an enrichment in ¹³C. These changes are attributed to reactions with free radicals, produced by ionising radiation. In contrast, the progressive radiolytic alteration of bitumens proposed to have derived from the radiolytic polymerisation of methane into an organic solid produces, upon pyrolysis, PAH of increasing average size and degree of alkylation. This, the opposite of the trend observed in the irradiated complex-hydrocarbons mixtures, cannot be explained in terms of the radiolytic alteration of a pre-existing array of complex organic molecules. Instead, it suggests the gradual construction of PAH from smaller molecules, supporting the hypothesis of a methane origin. Radiolytic alteration is also associated with a previously unrecognised increase in the mean combustion temperature of organic matter. This leads to predictions regarding the combustion characteristics of the irradiated organic matter present on cometary nuclei. A full understanding of the relationship between the combustion characteristics of organic polymers, radiation dose and the atomic H/C ratio should lead to the better design and implementation of in situ extraterrestrial sample analysis hardware and aid the interpretation of data from such missions. This study establishes predictable organic chemical responses of organic matter, upon exposure to ionising radiation. Our results support proposals that extraterrestrial PAH may be formed by the cosmic irradiation of simple hydrocarbons in interstellar ices. Our data may also be relevant to analogous material formed in other hydrocarbon-rich environments, such as the surface and atmosphere of Titan and other icy bodies, such as comets, and to the results of in situ analyses of extraterrestrial organic matter.