Individual Hydrocarbon Composition Research Articles

Integrated approach to determining the identity of the pollution of adjacent territories with oil products

The methodology of arranging laboratory studies of oil-contaminated soils, soils and bottom sediments to determine the source and composition of hydrocarbon contamination is described. The complex approach to laboratory analysis of samples of oil-contaminated soils, soils and bottom sediments is proposed, which allows a highly reliable identification of the potential source of contamination and/or making conclusions about the identity of the contamination of adjacent territories. The proposed complex of analytical methods includes infrared spectrometry, gas chromatography with mass-selective detection, thin-layer chromatography with flame ionization detection and elemental analysis (C, H, N, S, O). Application of the proposed integrated approach allows highly reliable determination of the nature of oil contamination of soils, estimation of the total gross content of oil products and their hydrocarbon composition, and identification of the potential source of pollution. Possible errors in the interpretation of the results of determining the identity of contamination of territories and the importance of using an integrated approach in drawing conclusions about the source (culprit) of pollution are shown using real soil samples taken from oil-contaminated objects and adjacent territories. The importance of taking into account the losses of volatile oil products at the stage of sample preparation for soil contamination with light oil fractions is demonstrated. The use of standard methods of sample preparation (drying of the samples under study) leads to errors in assessing the level of contamination of territories with volatile hydrocarbons and in the choice of methods of remediation of contaminated territories. To minimize losses of volatile hydrocarbons (petrol and naphtha fractions) at the stage of soil sampling and transportation the use of sorbent is proposed. Addition of a sorbent to the soil contaminated with oil products can reduce losses of volatile hydrocarbons by 15 – 20% in the analyzed samples. Application of the developed complex approach makes it possible to determine the features of the individual hydrocarbon composition, group and elemental composition of petroleum products and identify hydrocarbon indicators (markers) inherent only to a certain type of petroleum product.

Composition of gasolinefractions of Kumkol oil and improvement of theiroperational properties

The physicochemical properties of gasoline fractions of paraffinic oil from the Kumkol field have been investigated and the distinctive features of the individual hydrocarbon composition of the straight-run gasoline fraction and catalytic reforming gasoline have been established. The wide straight-run gasoline fraction (62-180°C) of Kumkol oil was subjected to preliminary hydrotreating at an industrial unit that is part of the catalytic reforming unit using S-12T and GO70 catalysts at a process temperature of 315 – 343°C, a pressure in the reactor of 21 – 27 atm, a volume feed rate of 6.4 – 9.4 h-1, with the circulation of HCG (Hydrogen-containing gas) «on the duct». Conditions under which catalytic reforming was carried out: temperature in the reaction zone – 470 ÷ 500°C, pressure – 28 kgf/cm2 , volumetric feed rate of raw materials – 1.5 h-1, gas circulation – 5.9 mol H2 / mol of raw materials. It has been established that in the process of reforming, as a result of isomerization of n-paraffins and dehydrogenation of cylanes, isoparaffin and aromatic hydrocarbons are intensively formed in the composition of reformant, and thereby the octane number of reforming gasoline is sharply increased. Gasoline obtained in the process of catalytic reforming from a narrow fraction of Kuikol oil meets the requirements for commercial, high-octane grades of motor fuel in all quality indicators. A significant synergistic effect has been established with the combined action of a two-component mixture compared to that for individual additives: a small concentration of the additive Hightech (manganese-containing) 18 mg/l and oxygen-containing AHA (ash-free high-octane additive) increases the octane number M.M. (motor method) by 3.3 points and according to R.M. (research method) by 5.3 points, and when introducing the additive Hitech 18 mg/l in a mixture with N-methylaniline, the increase in the O.N. (octane number) for M.M. was 4.4 units, and for R.M. (research method) – 6.

Geochemical fingerprints of Dongpu Depression crude oils in Bohai Bay Basin, northern China: Insights from biomarkers and isotopic compositions of selected alkylnaphthalenes and alkylphenanthrenes

The Dongpu Depression is a rift lake in the Bohai Bay Basin of eastern China, where abundant oil and gas resources were discovered. Previous geochemical investigations of Dongpu Depression oils have revealed a notable lack of data regarding the isotopic compositions of individual polycyclic aromatic hydrocarbons (PAHs) from the discovered Cenozoic crude oils. Using gas chromatography-mass spectrometry (GC–MS) and gas chromatography-isotope ratio mass spectrometry (GC-IRMS), a novel approach combining molecular parameters and stable carbon isotope compositions of individual PAH was applied to study the depositional environment conditions, the different source inputs, the maturation stage and to identify the potential family of five crude oils selected from Dongpu Depression.A decrease of Ga/C30H together with low Pr/Ph ratios and changes in isotopic compositions indicate that the five Dongpu Depression oils were derived from OM deposited in an anoxic saline environment with a stratified water column where mixing of saline water and freshwater occurred. The low isoprenoid, tricyclic and tetracyclic terpane ratios in combination with the δ13C values of 1,6-DMN, 1,2,5-TMN, 1,3,6,7-TeMN, 9-MP and 1-MP attest that their sources have a mixed origin with high aquatic organism (planktonic) input and a lower land plant (C3 plant) contribution. The δ13C values of phenanthrene between −30.0 ‰ and −20.0 ‰ indicate that the studied Dongpu Depression oils belong to a single family generated from the peak to the late oil generation stage (Rc-TNR-2 between 0.85 and 1.15 %). A correlation with various basins indicates that oil samples featured by δ13C values of Phen between −30.0 ‰ and −20.0 ‰ correspond to crude oils derived from mixing of aquatic and high plant contributions with different degrees of mixtures, which have not yet reached their cracking stage (Rc < 2.0 %). Crude oils from the Carboniferous and Mesozoic-Cenozoic Tarim rocks, Australian petroleum systems, Termit Basin, Bongor Basin, Fushan Depression and the studied Dongpu Depression oils belong to that group of oils. Crude oils characterized by lighter phenanthrene isotopic compositions (δ13C values of Phen < −30.0 ‰) are mainly derived from marine/aquatic input and have already entered the cracking window (Rc > 2.0 %). This group of oils is represented in this study by the Cambrian-Ordovician Tarim Basin oil samples. The research shows the importance of the aromatic isotopic compositions in petroleum system characterization and could be used as a reference for a practical exploration campaign of petroleum.

Carbon isotopic compositions of mono-, di-, tri-aromatics provide insights into the source of sulfur-rich crude oils in the Huanghekou Depression, Bohai Bay Basin

The stable carbon isotope compositions (δ13C) of individual aromatic hydrocarbons have been analyzed in sulfur-rich and sulfur-lean crude oils from the Huanghekou depression, Bohai Bay Basin. The δ13C values of individual aromatic hydrocarbons, including alkylbenzenes, alkylnaphthalenes, alkylphenanthrenes, alkylfluorenes and alkyldibenzothiophenes, are reported. The main aims are to find out the origin of these oils and their relationship to paleoclimate. The distribution of aromatic hydrocarbons and maturity parameters show the oils all stay in the low-mature to mature stage. Meanwhile, aromatic hydrocarbons are mainly derived from the diagenetic/catagenetic origin. The δ13C values for 1,2,4-trimethylbenzene (−30.7‰ to −28.8‰) and 1,2,3,4-tetramethylbenzene (−32.4‰ to −26.3‰) indicate the algae-derived organic matter for alkylbenzenes. Some isomers, such as 1,7-+1,3-+1,6-dimethylnaphthalene, 1,2,5-trimethylnaphthalene, 1,2,5,6-+1,2,3,5-tetramethylnaphthalene, 1,10- + 1,3- + 3,10- + 3,9-dimethylphenanthrenes, 1,6- + 2,9- + 2,5- dimethylphenanthrenes and 4,9- + 4,10- + 1,9- dimethylphenanthrenes show isotopic depletion (−34.9‰ to −25.2‰), indicating the major contribution of algae for these compounds. Meanwhile, isotopically depleted (−33.6‰ to −26.7‰) alkyldibenzothiophenes represent the algae input. δ13C values for mainly algae-derived naphthalene to trimethylnaphthalenes of sulfur-rich oils are more enriched than those of sulfur-lean oil, with the most significant difference of 4.4‰, indicating that the aridity of the environment and stratified water column result in the enrichment in 13C.

Stable carbon isotopic compositions of individual light hydrocarbons in the C5–C7 range in natural gas from the Qaidam Basin, China

C5–C7 light hydrocarbons are important components in petroleum and are extensively employed as an auxiliary approach in petroleum research. Consensus on the mechanism of light hydrocarbon generation has not yet been achieved. In this study, 20 gas samples were collected from the western part and northern margin of the Qaidam Basin. The molecular and carbon isotopic compositions of C1–C3 gaseous hydrocarbons and C5–C7 light hydrocarbons, as well as the carbon isotopes of oils were analyzed. Based on the relationships between carbon isotopes (13C) of individual light hydrocarbons and calculated vitrinite reflectance, it suggests that organic matters play a fundamental role in the carbon isotopes of light hydrocarbons, and maturity mainly affects the carbon isotopes of n-alkanes in light hydrocarbons. In addition, carbon isotopic differences between n-, iso- and cyclo-alkanes indicate that light hydrocarbons with different structures are produced from various biological precursors. Besides, carbon isotopes of individual light hydrocarbons can be used to estimate the δ13Ckerogen and distinguish cracked gas. On the one hand, small isotope fractionation between iso-alkanes and kerogen is observed. Average carbon isotopic compositions of iso-pentane ( i-C5), 2-methylpentane (2-MC5) and 3-methylpentane (3-MC5) can provide a similar δ13Ckerogen with actual values. On the other hand, the carbon isotopic difference between 2-MC5 and n-C6 generally decreases with increasing maturity. Combined with the parameter (2-MC6 + 3-MC6)/ n-C6, kerogen-cracked gases are characterized by high δ13C2MC5–δ13CnC6 and low (2-MC6 + 3-MC6)/ n-C6 values, whereas oil-cracked gases exhibit the opposite features.

Compositional analysis of light oil fractions from deep-water Guneshli field

Hydrocarbon composition of the fraction with 150–300 оС boiling point of oil from deep-water Guneshli field has been studied. The oil is characterized with light, oily, low sulphur, low-in-tar, paraffinic structure (3.7 % mass of solid paraffin), without asphaltenes. The fraction with 250–300 оС boiling point has been divided into naphteno-paraffinic and aromatic hydrocarbon groups using the method of liquid elution-adsorption chromatography. The individual hydrocarbon composition of naphteno-paraffinic hydrocarbons has been studied via chromato-mass-spectroscopy and the structure-group composition of the arenes using PMR-spectroscopy, correspondingly. Isoprenoid С13–С15 and С18, as well as 0.54 % mass of pristane biomarkers (С19) and phytane (С20) biomarkers have been revealed in the composition of naphteno-paraffinic hydrocarbons. the nuclear are enriched in the paraffinic structures in the form of substituent.

Increasing the Yield of Light Distillates by Wave Action on Oil Raw Materials

The article presents the results of the electromagnetic activation of petroleum feed in the vortex layer apparatus. It is shown that under the electromagnetic influence, there is a significant increase in the proportion of straight-run gasoline fraction distillate, as well as a change in the physicochemical parameters of the light fractions obtained as a result of the cavitation effect and the low-temperature cracking. It has been established that the processes of wave action on oil occurring in the electromagnetic field zone lead to a change in the individual and group hydrocarbon composition of the distillates obtained. The gasoline fraction produced from activated petroleum, due to an increase in the proportion of aromatic compounds, has a high octane number compared to the original straight-run fraction and low content of alkenes, which allows us to recommend its use as a high-octane component of motor fuels in the compounding and production of commercial gasoline.

Virtual Soft Sensor of the Feedstock Composition of the Catalytic Reforming Unit

The paper discusses a method for obtaining a matrix of individual and group composition of a hydrotreated heavy gasoline fraction in industrial conditions based on the fractional composition obtained by the distillation method according to the ASTM D86 (the Russian analogue of such a standard is GOST 2177). A method for bounds estimation of the retention index (RI) change is considered on the basis of the symmetry of the RI change range relative to its arithmetic mean. Implementation of this method is performed by simulation of individual composition of C6–C12 feedstock of the catalytic reforming unit in the software package. For this purpose, the boiling curve of individual composition of hydrocarbon mixture is converted into the corresponding curve of fractional composition. The presented technique of creating a virtual soft sensor makes it possible to establish a correct relationship between the fractional composition and the individual hydrocarbon composition obtained according to the IFP 9301 (GOST R 52714) (Russian GOST R 52714 and international IFP 9301 standards for the determination of individual and group composition of hydrocarbon mixtures by capillary gas chromatography). The virtual soft sensor is based on chemical and mathematical principles. The application of this technique on the data of a real oil refinery is shown. Obtaining accurate data by means of a virtual soft sensor on the individual composition of feedstock will make it possible to optimize the catalytic reforming process and thus indirectly improve its environmental friendliness and enrichment efficiency.

Hydro-catalytic isomerization of light gasoline fraction of Zhanazhol field’s oil

The purpose of the present work is to show that light straight-run gasoline fraction can be used as feedstock for hydro-catalytic isomerization process, and the isomerized product can serve as a component for obtaining pure ecological commercial gasoline brand Euro-4 and Euro-5. Transformation of n-alkanes of Zhanazhol oil’s light gasoline fraction with boiling temperature 180°C was studied. Isomerization was carried out in a flow unit with a stationary layer of modified sample of industrial aluminum-platinum catalyst at 200-300°C and 2.0-4.0 MPa, with volume feed rate of 1.0-3.0 h-1 and circulation ratio of hydrogen containing gas circulation 1000-1500 m3/m3 of catalyst feed. Light gasoline fraction are subjected to a number of chemical transformations: n-paraffins isomerization, five-membered and six-membered cycloalkanes dehydroisomerization and hydrocracking. n-Alkanes are isomerized in iso-alkanes, naphthenic hydrocarbons are first subjected to hydrocracking with opening the cycle and forming n-alkanes, which are then isomerized into iso-alkanes. Thus, the reaction products contain isopentane, 2,3-dimethylbutane with octane number 92 and 104 correspondingly, and other iso-paraffinic hydrocarbons that lead to raise of gasoline octane number. By study of individual hydrocarbon composition of feedstock and isomerizate it is possible to establish some regularities hydrocarbons in the process of hydro-catalytic isomerization of light gasoline fraction.

Thermogravimetric Determination of the Kinetics of Petroleum Needle Coke Formation by Decantoil Thermolysis.

This work presents the results of thermogravimetric analysis of decantoil. The microstructure of the extracted petroleum coke during the thermolysis of decantoil in an inert nitrogen atmosphere at 1000 °C was studied by scanning electron microscopy and interpreted as acicular. The model free kinetic approach based on Friedman’s isoconversion method was used to calculate the kinetic characteristics of decantoil thermolysis-activation energy and pre-exponential factor. The individual hydrocarbon composition of decantoil was determined by gas chromatography mass spectrometry, which was used to determine the activation energy of evaporation of its fractions. The total energy spent on the chemical reactions of cracking and thermopolycondensation was determined when the degree of decantoil conversion was changed from 0.1 to 0.9.

Каталитический риформинг бензиновой фракции смеси нефтей Южного региона Республики Казахстан

В статье рассматриваются результаты исследования процесса каталитического риформинга прямогонного бензина, полученного из смеси нефти месторождений, расположенных в Южном регионе Казахстана. Изучен индивидуальный и групповой углеводородный состав исходного гидроочищенного бензина и риформата с целью установления степени превращения углеводородов на разных этапах каталитического риформинга. В результате исследования процесса каталитического риформинга прямогонного бензиновой фракции (85–180°С) установлен химизм и механизм реакций, которые основываются на следующих реакциях: дегидроциклизация парафиновых углеводородов, дегидрирование и дегидроизомеризация нафтеновых, изомеризация нафтеновых и парафиновых углеводородов. Сравнение физико-химических свойств и группового углеводородного состава гидрогенизата и продуктов риформинга показывает, что сумма н-парафиновых и нафтеновых углеводородов после каталитического риформинга уменьшается в 3–4 раза по сравнению с исходным бензином, а концентрация ароматических углеводородов значительно возрастает за счет реакции дегидрирования цикланов и дегидроциклизации нормальных парафинов.

Optimization of the Pyrolysis of Naphtha Fractions of the West Siberian Gas Condensate to Obtain Lower Olefins and Divinyl

Naphtha fractions of the West Siberian gas condensate were evaluated as feedstock for thermal pyrolysis performed in the temperature interval 750–900°C at the conventional contact time of 0.2–0.4 s and steam-to-feed weight ratio of (0.5; 0.8): 1.0. Statistical models of the process, based on the experimental dataset obtained, were constructed and used for multicriteria optimization with respect to the key products: ethylene, propylene, divinyl, pyrogas, and coke. The optimum process parameters for pyrolysis of light and heavy naphtha of the gas condensate to reach the maximal yield of target products (ethylene, propylene, divinyl) under the conditions of compromise solutions were found. The influence of the group and individual hydrocarbon composition of the naphtha fractions of the gas condensate on the yield and distribution of the major products was demonstrated.

Stable carbon isotopic composition of light hydrocarbons and n-alkanes of condensates in the Tarim Basin, NW China

The carbon isotope ratios of individual light hydrocarbons and the n-alkanes of twenty-one condensates from the Tarim Basin, as well as 47 condensates and oils from other petroliferous basins (Ordos Basin, Sichuan Basin, Turpan-Harmi Basin, Qiongdongnan Basin, Beibu Gulf Basin and Bohai Bay Basin) in China, were analyzed. We investigated the oil–oil correlation, the effects of gas washing and maturity, as well as the distinguishing parameters of humic and sapropelic condensates, and have come to the following conclusion. The carbon isotopic patterns of condensates and oils in the Ordovician strata of Tarim Basin are very similar, indicating they originate from the same type of source rocks. The condensates from Dawanqi oil field and Yinan 2, as well as Ti'ergen and Yitikelike gas fields, have similar carbon isotopic patterns. Thus, they probably have originated from the same terrestrial Jurassic source rock. The carbon isotopic patterns of the condensates from the Dabei, Kela 2, and Keshen gas fields are also similar, indicating they are of the same oil family and sourced from the Triassic and Jurassic terrestrial source rock. The carbon isotopic ratios of 2-MP, 3-MP, 3-MH, and nC5-8 are much more susceptible to maturity level than other light hydrocarbons. Gas washing has minor effects on the δ13C compositions of individual light hydrocarbons and n-alkanes, although it causes <2‰ shifts. The δ13C compositions of MCP, CH, MCH, benzene, and toluene can be used as identification parameters for humic and sapropelic condensates. Humic condensates generally have δ13CMCP > −25‰, δ13CCH > −24‰, δ13CMCH > −24‰, δ13Cbenzene > −25‰, and δ13Ctoluene > −24‰, whereas sapropelic condensates mainly have δ13CMCP < −26‰, δ13CCH < −26‰, δ13CMCH < −24‰, δ13Cbenzene < −25‰ and δ13Ctoluene < −24‰. Moreover, the mixing humic and sapropelic condensates usually show intermediate values.

Hydrocarbon composition of bitumen from deeply buried terrestrial organic matter (zone of apocatagenesis)

We present new results catagenetic alteration of dispersed organic matter (DOM) and individual hydrocarbon composition of bitumen extracts from the lower mesocatagenesis and apocatagenesis zone, based on the study of core samples from superdeep well SV-27 (Vilui syneclise), which penetrated Permian and Upper Carboniferous coal-bearing strata. The vitrinite reflectance data show a progressive increase in the thermal maturity of DOM at a depth of ~4 km. The major biomarker indicators of the thermal history of DOM in the central part of the Vilyui syneclise appear to play only a minor role below this depth, thus reflecting the early stages of mesocatagenesis. The pristane/phytane ratios begin to invert at the same depth. Bitumen extracts from core samples collected from this depth contain new hydrocarbons in trace amounts, which increase with depth. The identified compounds include homologous series of alkenes, 2,4- and 2,7-dimethylalkanes, and alkylcyclohexanes with a prevalence of compounds with an odd carbon number predominance. Unusual differentiation of aliphatic and cyclic hydrocarbons with even and odd carbon-numbered chains occurs at the maximum depth (6458 m). Among aromatic hydrocarbons, four new diastereomers are identified: 17-desmethyl–23-methylmonoaromatic steroids C27. Considerable variations in the composition of bitumen extracts from the apocatagenetically altered core samples appear to reflect the termination of hydrocarbon generation from kerogen and further thermolysis of residual bitumens, including their asphaltene components. This explains the low values of maturity biomarker indicators corresponding to the apocatagenesis grade, since in this case they reflect the composition of hydrocarbons generated during the early stages and later occluded and adsorbed by asphaltenes. “Deep-seated” microoil from Permian, Carboniferous, and Cambrian deposits did not participate in the formation of oil rims and major gas condensate pools in the Vilyui petroleum area.

Accumulation process and pattern of oolitic shoal gas pools in the platform: A case from Member 3 of Lower Triassic Feixianguan Formation in the Heba area, northeastern Sichuan Basin

Abstract Combined with the regional sedimentary burial history and trap tectonic evolution history, the gas source, pool-forming periods and accumulation process of the oolitic shoal limestone gas pool in the Lower Triassic Feixianguan Formation Member 3 were researched in the Heba area of northeast Sichuan Basin. The gas source was mainly derived from the underlying Upper Permian Wujiaping Formation (or Longtan Formation) according to the analysis results of carbon isotopic compositions of individual hydrocarbons. The analysis of homogenization temperature for fluid inclusions shows, the gas pool has experienced multi-stage gas charging and migration, which occurred in the Late Jurassic to Early Cretaceous, matched with the generating peak of the Upper Permian source rocks, and represented the main period for hydrocarbon accumulation. The structure formation process of the Heba area had structural prototype in Indo-Chinese Epoch, and was relatively stable stage in the Jurassic to Early Cretaceous, and was formed like present structure in the Late Cretaceous, and was complicated in the Cenozoic Himalayan period. It is predicted that the sedimentary micro-paleogeomorphology highs, faults or fracture relative development area and the ancient-modern structure development zone are favorable for oolitic shoal limestone gas pools in Northeast Sichuan.

Influence of thermal maturity on carbon isotopic composition of individual aromatic hydrocarbons during anhydrous closed-system pyrolysis

Anhydrous closed-system pyrolysis experiments were conducted on the pure alkyl naphthalenes, n-alkanes and three crude oils at the highly to over mature stage in order to investigate compositional and isotopic changes of individual aromatic hydrocarbons during laboratory maturation. On the whole, aromatic hydrocarbons have better thermal stability than n-alkanes. While the carbon isotopic composition of substituted aromatic hydrocarbons exhibits a positive correlation with increasing thermal maturity, there is no significant fractionation in the carbon isotopic composition of unsubstituted aromatic hydrocarbons. This finding suggests that the carbon isotopic distribution of unsubstituted aromatic hydrocarbons can be used as an effective tool for oil-oil and oil-source correlation, especially for highly-over mature fields.

Petroleum source, maturity, alteration and mixing in the southwestern Barents Sea: New insights from geochemical and isotope data

The Hammerfest Basin (HB) is an important area for petroleum exploration in the southwestern Norwegian Barents Sea. This contribution is aimed to characterize oils and condensates hosted in Triassic and Jurassic reservoirs, establish genetic relationships and to assess maturity, mixing and petroleum alteration processes. The research was based on geochemical as well as bulk and compound-specific stable carbon and hydrogen isotope analyses of oil and condensate samples from all major fields and discoveries in the HB, including extracts from Jurassic and Triassic source rocks. Interpretations of light hydrocarbon composition and isotope data clearly identify four main petroleum groups affected by microbial degradation, water washing, evaporative fractionation and high thermal maturity level. Based on polycyclic aromatic hydrocarbons (PAHs), marine and higher-plant-derived biomarkers and carbon isotopic composition (δ13C) of individual petroleum hydrocarbons, four petroleum families (I–IV) are recognized in the HB and a distinction can be made among oils and condensates from different stratigraphic levels and sectors of the Basin. Most oils and condensates from the HB consist of mixtures with small maturity variations; however, oils from Middle Triassic reservoirs in the Goliat field showed larger maturity variations according to biomarker, PAH and light hydrocarbon–maturity ratios. In the HB, geochemical and isotopic data allowed unraveling mixtures of hydrocarbons derived mainly from Jurassic, Triassic and Paleozoic source rocks.

A multiple endpoint analysis of the effects of chronic exposure to sediment contaminated with Deepwater Horizon oil on juvenile Southern flounder and their associated microbiomes

Exposure to oiled sediments can negatively impact the health of fish species. Here, we examine the effects of chronic exposure of juvenile southern flounder, Paralichthys lethostigma, to a sediment-oil mixture. Oil:sediment mixtures are persistent over time and can become bioavailable following sediment perturbation or resuspension. Juvenile flounder were exposed for 32 days under controlled laboratory conditions to five concentrations of naturally weathered Macondo MC252 oil mixed into uncontaminated, field-collected sediments. The percent composition of individual polycyclic aromatic hydrocarbons (PAHs) of the weathered oil did not change after mixing with the sediment. Spiked exposure sediments contained 0.04–395mg/kg tPAH50 (sum of 50 individual PAH concentration measurements). Mortality increased with both exposure duration and concentration of sediment-associated PAHs, and flounder exposed to concentrations above 8mg/kg tPAH50 showed significantly reduced growth over the course of the experiment. Evident histopathologic changes were observed in liver and gill tissues of fish exposed to more than 8mg/kg tPAH50. All fish at these concentrations showed hepatic intravascular congestion, macrovesicular hepatic vacoulation, telangiectasia of secondary lamellae, and lamellar epithelial proliferation in gill tissues. Dose-dependent upregulation of Cyp1a expression in liver tissues was observed. Taxonomic analysis of gill and intestinal commensal bacterial assemblages showed that exposure to oiled sediments led to distinct shifts in commensal bacterial population structures. These data show that chronic exposure to environmentally-relevant concentrations of oiled sediments produces adverse effects in flounder at multiple biological levels.

The distribution characteristic and its significance of compound specific isotopic composition of aromatic hydrocarbon from marine source rock and oil in the Tarim Basin, western China

Aromatic hydrocarbons are generally main distillation of crude oil and organic extract of source rocks. Bicyclic and tricyclic aromatic hydrocarbons can be purified by two-step method of chromatography on alumina. Carbon isotopic composition of individual aromatic hydrocarbons is affected not only by thermal maturity, but also by organic matter input, depositional environment, and hydrocarbon generation process based on the GC-IRMS analysis of Upper Ordovician, Lower Ordovician, and Cambrian source rocks in different areas in the Tarim Basin, western China. The subgroups of aromatic hydrocarbons as well as individual aromatic compound, such as 1-MP, 9-MP, and 2,6-DMP from Cambrian-Lower Ordovician section show more depleted 13C distribution. The δ13C value difference between Cambrian-Lower Ordovician section and Upper Ordovician source rocks is up to 16.1‰ for subgroups and 14‰ for individual compounds. It can provide strong evidence for oil sourc correlation by combing the δ13C value and biomarker distribution of different oil and source rocks from different strata in the Tarim Basin. Most oils from Tazhong area have geochemical characteristics such as more negative δ13C9-MP value, poor gammacerane, and abundant homohopanes, which indicate that Upper Ordovician source rock is the main source rock. In contrast, oils from Tadong area and some oils from Tazhong area have geochemical characteristics such as high δ13C9-MP value, abundant gammacerane, and poor homohopanes, which suggest that the major contributor is Cambrian-Lower Ordovician source rock.

The effect of origin and genetic processes of low molecular weight aromatic hydrocarbons in petroleum on their stable carbon isotopic compositions

Stable carbon isotopic compositions of individual low molecular weight aromatic hydrocarbons, such as alkylbenzenes, alkylnaphthalenes and alkylphenanthrenes, were measured from a set of oils, mostly from the North-West shelf of Australia, of varying age, facies type and thermal maturity. The objective was to assess the influence of thermal maturity and source during generation of these aromatics on their stable carbon isotopic compositions. For most of the oils studied, δ13C of the aromatic components show a 13C depletion as the degree of methylation increases. For the alkylnaphthalenes, the 13C depletion is most pronounced for low maturity oils compared to high maturity oils. δ13C of the methyl groups of these alkylnaphthalenes were calculated and the resulting data display significant differences between ‘mature’ and ‘immature’ oils, suggesting that isotopically lighter methyl groups are ‘released’ as thermal maturation proceeds. Therefore, we propose an isotopic fractionation associated with the methyl transfer mechanisms affecting low molecular weight aromatic hydrocarbons during diagenesis.