N-alkanes In Crude Oil Research Articles

Determination of N-Paraffins Content in Crude Oil via Near-Infrared Spectroscopy Associated with Chemometric Approaches

This study explores the potential application of NIR spectroscopy coupled with different linear and nonlinear models for rapid evaluation of n-alkanes in crude oil. Samples for calibration were 30 model mixtures of n-eicosane in crude oil samples with a concentration of 1–15%. The prediction models were established based on 21 methods: linear regression, regression trees, support vector machines, Gaussian process regression, ensembles of trees, and neural networks. The spectral range 4500–9000 cm−1 was determined to be the most informative for prediction. The prediction capability of lineal regression methods turned out to be unsatisfactory. Nonlinear models were preferred over linear models; better results were obtained using the regression trees method, including «fine tree» (RMSE = 2.8635) and neural networks (RMSE = 2.0157). The LS-SVM model exhibited satisfactory prediction performance (R2 = 0.96, RMSE = 0.91), as did the Gaussian Process Regression Matern 5.2 GPR (R2 = 0.96, RMSE = 1.03) and Gaussian Process Regression (Rational Quadratic) (R2 = 0.95, RMSE = 1.04). Among the 21 chemometric algorithms, the best and weakest models were the LS-SVM and PLSR models, respectively. The LS-SVM model was the optimal model for the prediction of n-alkanes content in crude oil.

Combined microbial degradation of crude oil under alkaline conditions by Acinetobacter baumannii and Talaromyces sp

The purpose of this work was to study the biodegradation of crude oil under alkaline condition by defined co-culture of Acinetobacter baumannii and Talaromyces sp. The n-alkanes in crude oil could be completely degraded by bacteria and fungi with the ratio of 1:1 at pH 9 in 14 d water simulation experiment. Meanwhile, the total degradation rate of crude oil could reach 80%. Fungi had stronger ability to degrade n-alkanes, while bacteria could better degrade other components such as aromatics and branched alkanes. The two strains were both capable of producing a small amount of biosurfactant. High cell viability was the main factor for strains to exert high degradation ability in alkaline environment. It was preliminarily verified that bacteria and fungi rely on the differences of enzyme systems to achieve synergy in the degradation process. These results indicated that the defined co-culture had great potential for bioremediation in alkaline soils.

Biodegradation of n-alkanes in crude oil by three identified bacterial strains

In this study, aerobic biodegradation of crude oil was simulated using Pseudomonas aeruginosa XJ16, Bacillus cereus XJ20, and Acinetobacter lwoffii XJ19 bacteria for 90 days, for semi-quantitative calculation of concentration, demonstrating that n-alkanes (C14–C35) were biodegraded by the three strains at different ratios and rates. P. aeruginosa XJ16 showed the highest biodegradative potential for n-alkanes, with total biodegradation ratio of 98.2% in 10 days. In comparison, the total biodegradation ratio by B. cereus XJ20 increased gradually and achieved 98.8% after 90 days; whereas that by A. lwoffii XJ19 was much lower even after 90 days (29.3%). In addition, P. aeruginosa XJ16 and B. cereus XJ20 exhibited stronger biodegradation efficiencies for C18–C32n-alkanes (95.4%–99.7%) than A. lwoffii XJ19 (9.05%–73.0%). However, all three bacterial strains exhibited comparably good biodegradation efficiencies for C33–C35n-alkanes (60.2%–86.4%). Moreover, the biodegradation rate constants and biodegradation rates were of the decreasing order: P. aeruginosa XJ16 > B. cereus XJ20 > A. lwoffii XJ19. P. aeruginosa XJ16 and B. cereus XJ20 biodegrade n-alkanes with relatively low carbon numbers more easily than those with high carbon numbers. However, A. lwoffii XJ19 is more likely to biodegrade n-alkanes with relatively high carbon numbers. On day 10, surface tension (mN·m−1) declined from 70.6 to 35.9 by treatment with P. aeruginosa XJ16, to 31.3 with B. cereus XJ20, and to 34.1 with A. lwoffii XJ19. As biosurfactant-producing and hydrocarbon-degrading bacteria, these three strains have the potential to be used for bioremediation of hydrocarbon pollutants.

Preferential degradation of long-chain alkyl substituted hydrocarbons in heavy oil under methanogenic conditions

Methanogenic crude oil degradation is a significant process in subsurface environments and degradation of crude oil n-alkanes has been well documented. However, little is known about the biodegradability of the resulting heavy oil. In this study, a methanogenic consortium enriched from Shengli oilfield generated 1.3–1.9 mmol CH4/g of heavy oil at a rate of 2.9–8.8 μmol CH4/g of oil/day. Four SARA fractions (saturates, aromatics, resins and asphaltenes) of oils experienced a loss in linear aliphatic structures. n-Alkylcyclohexanes, methyl-n-alkylcyclohexanes, n-alkyldecalins, n-alkylbenzenes, n-alkyltoluenes and n-alkylxylenes with alkyl side chains longer than 14 carbons were degraded over 50% compared to the undegraded oil. In addition, the extent of degradation of these hydrocarbons increased with increasing carbon length. Correspondingly, n-fatty acids and naphthenic acids with 1–3 naphthenic rings accumulated over time. 16S rRNA gene analysis revealed that aceticlastic Methanosarcina and Methanothrix dominated in the archaeal domain, and bacterial members related to Dehalococcoidia and Soehngenia were consistently present in the successive transfer cultures. However, neither assA/masD-like genes nor alkyl-substituted succinate metabolites were detected, indicating an alternative degradation pathway, rather than addition to fumarate. This study provides novel insights into methanogenic degradation of long-chain alkyl substituted hydrocarbons in heavy oil, which also extends our understanding of anaerobic degradation of crude oil in subsurface sedimentary environments.

Promoting the treatment of crude oil alkane pollution through the study of enzyme activity

Microbes appear to play a key role in bioremediation of petroleum hydrocarbons pollution and little attention has been paid to the enzyme activity in the process of alkane bioremediation. Oil field bacterium identified as Pseudomonas synxantha LSH-7′ was chosen as the tested strain. Periodically collected samples were analyzed by GC-FID (Gas Chromatography- Flame Ionization Detector) and RT-qPCR (Quantitative-Real-Time-PCR). GC-FID results showed this bacterial strain has great degradation ability on crude oil n-alkanes and RT-qPCR data indicated the differences between the three genes expression including AlkB-, Cytochromes P450-, and almA- related when grown on different-chain alkanes. Meanwhile, enzyme activity like alkane hydroxylase, alcohol dehydrogenase, dehydrogenase, protease, phosphatase, catalase and lipase were measured. Extracellular alkane hydroxylase was induced in a higher degree than intracellular in the early incubation time, alcohol dehydrogenase increased/decreased along with alkane hydroxylase, and the pH of the medium obviously decreased. Other enzymes were also described including dehydrogenase activity that reached a highest point that was slower than alcohol dehydrogenase, protease activity started multiplying after a period of culture while biomass was immediately increased, catalase activity dramatically enhanced in the presence of alkanes, phosphatase activity was closely linked to pH approximately but lipase activity was found to be moderate.

Variations of Acidic Compounds in Crude Oil during Simulated Aerobic Biodegradation: Monitored by Semiquantitative Negative-Ion ESI FT-ICR MS

Simulations of aerobic biodegradation have been widely employed to investigate the mechanisms of crude oil biodegradation in geological environments. In this study, a simulated biodegradation experiment was performed with crude oil under aerobic conditions, in which n-alkanes were nearly depleted, thus providing an opportunity to study the biodegradation mechanisms of n-alkanes in crude oils. The sequences of biodegraded oils with a slight to moderate degree of biodegradation were characterized by negative-ion electrospray (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography (GC). Semiquantitative results on the molecular compositions of heteroatom classes were obtained by coinjection of internal standards. The biodegradation mechanisms for n-alkanes and n-fatty acids, as well as some other heteroatomic compounds, are discussed. Evidence from FT-ICR MS and GC analyses of biodegraded oils indicates that n-alkanes can be progressively biodegraded to n-fatty ac...

Detection of n-alkane biodegradation genes alkB and ladA in thermophilic hydrocarbon-oxidizing bacteria of the genera Aeribacillus and Geobacillus

Ability to degrade crude oil n-alkanes was revealed in new strains of thermophilic bacilli isolated from petroleum reservoirs and a hot spring: Geobacillus toebii В-1024, Geobacillus sp. 1017, and Aeribacillus pallidus 8m3. The strains utilized С10–С30 n-alkanes (В-1024), С10, C11, and С13–С19,22 n-alkanes (1017), and C11–C29 n-alkanes (8m3). In all three strains, PCR amplification with specific degenerate oligonucleotide primers revealed the alkB gene encoding rubredoxin-dependent alkane monooxygenase. In strains В-1024 and 1017, fragments of the genes homologous to the ladA gene determining flavin-dependent alkane monooxygenase were also amplified. Nucleotide sequences of these genes were practically identical to those of the genes ladAαB23, ladAβB23, and ladB B23, which were revealed previously in Geobacillus thermoleovorans strain B23. For the latter strain, activity of respective enzymes in the oxidation of long-chain n-alkanes has been shown. Thus, simultaneous presence of the alkB and ladA genes coding alkane monooxygenases responsible for oxidation of medium-chain and long-chain n-alkanes in thermophilic bacilli was revealed for the first time.

Characteristics and origin of carbon isotopes of n-alkanes in crude oils from the western Pearl River Mouth Basin, South China sea

The quantitative characterization of carbon isotopes of n-alkanes is commonly carried out in organic geochemical studies. Possible controls on carbon isotopes include source organic matter, maturity, fractionation during oil expulsion and migration, and the mixing of different oils. In this study of the origin of crude oils in the western Pearl River Mouth Basin, the influences of all of these factors have been considered in reaching a conclusion. Carbon isotopes of n-alkanes in the crude oils, and the extracts of the two effective source rocks (the Wenchang and Enping formations) in the basin, exhibit clear differences. The Wenchang source rocks have heavy δ13C values that remain almost constant or become slightly heavier with increasing carbon number. The Enping source rocks have light δ13C values that become lighter with increasing carbon number. Two groups of oils in this area were identified based on the carbon isotopes of the n-alkanes; groupIoils are similar to extracts of the Wenchang source rocks. However, the groupIIoils are different from both the Wenchang and Enping source rocks and the carbon isotopic profiles of their n-alkanes exhibit a “V” feature with increasing carbon number. The results of artificial thermal maturation experiments indicate that, from the early stage to the peak stage of oil generation (with EasyRo between 0.64% and 1.02%), the δ13C values of n-alkanes in the pyrolysis oils become heavier by about 3‰ with increasing thermal maturity, but the shape of the carbon isotopic profiles are not significantly changed. Calculated δ13C values of n-alkanes in “mixed” artificial pyrolysis oils indicate that the mixture of oils generated from the same source rocks with different maturities could not change the carbon isotopic profile of the n-alkanes, however, a mixing of the Wenchang and Enping oils could give the “V” feature in the profiles, similar to the groupIIoils in this area. The groupIIoils appear to be mixed Wenchang and Enping oils, the latter being the dominant component in the mixture. We conclude that the source organic matter and the degree of mixing are the main factors controlling the carbon isotopic characteristics of n-alkanes in crude oils in the western Pearl River Mouth Basin.

Interaction Effects of Plants and Indigenous Micro-organisms on Degradation of N-Alkanes in Crude Oil Contaminated Agricultural Soil

Agricultural soil samples from mapped out areas for the study were aseptically collected with sterile plastic sample containers and microbiologically analyzed to isolate autochthonous microbial flora. Seeds of four annual crops including Vigna unguiculata var unguiculata, Mucuna pruriens, Zea mays and T occidentalis used were planted on the test soil and polluted with Bonny light crude oil twenty eight (28) days after plant growth. Thirty days after pollution, soil samples were collected within the rhizosphere of the test plants and examined microbiologically to isolate persisting microorganisms in the polluted soil. The variation in degradation of n-alkanes was ascertained seven days after pollution using Gas chromatographic analysis on soil samples and compared with the control. The pre microbial lab analysis of the soil under the study revealed culturally, the presence of PenicillIum sp Aspergillus fumigatus, Aspergillus niger, Candida sp, Pseudomonas fluorescence, Acinetobacter baumanni, Bacillus mycoides, Klebsiella sp., Staphylococcus aureus and Escherichia coli whereas the absence of the last two isolates was observed during post microbial analyses. Results of the GC analysis on comparison to the control sample depict that plants kept in the greenhouse were able to degrade alkanes within the range of C7 to C12 and C32 to C40 while samples in the field degraded alkanes within the range C7 to C15 and C36 to C40. M pruriens degraded C13. This study could be a promising tool in conversion of crude oil in contaminated agricultural soil to less toxic substances for enhanced remediation.

Progressive degradation of crude oil n-alkanes coupled to methane production under mesophilic and thermophilic conditions.

Although methanogenic degradation of hydrocarbons has become a well-known process, little is known about which crude oil tend to be degraded at different temperatures and how the microbial community is responded. In this study, we assessed the methanogenic crude oil degradation capacity of oily sludge microbes enriched from the Shengli oilfield under mesophilic and thermophilic conditions. The microbial communities were investigated by terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA genes combined with cloning and sequencing. Enrichment incubation demonstrated the microbial oxidation of crude oil coupled to methane production at 35 and 55°C, which generated 3.7±0.3 and 2.8±0.3 mmol of methane per gram oil, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that crude oil n-alkanes were obviously degraded, and high molecular weight n-alkanes were preferentially removed over relatively shorter-chain n-alkanes. Phylogenetic analysis revealed the concurrence of acetoclastic Methanosaeta and hydrogenotrophic methanogens but different methanogenic community structures under the two temperature conditions. Candidate divisions of JS1 and WWE 1, Proteobacteria (mainly consisting of Syntrophaceae, Desulfobacteraceae and Syntrophorhabdus) and Firmicutes (mainly consisting of Desulfotomaculum) were supposed to be involved with n-alkane degradation in the mesophilic conditions. By contrast, the different bacterial phylotypes affiliated with Caldisericales, “Shengli Cluster” and Synergistetes dominated the thermophilic consortium, which was most likely to be associated with thermophilic crude oil degradation. This study revealed that the oily sludge in Shengli oilfield harbors diverse uncultured microbes with great potential in methanogenic crude oil degradation over a wide temperature range, which extend our previous understanding of methanogenic degradation of crude oil alkanes.

Prediction of the Interaction between Crude Oil Wax-Crystal Fractions and Acrylate Polymers by Monte Carlo Simulation

The interaction between n-alkanes and pour point depressants with different structures was investigated. Using n-hexadecane as the representative component of crude oil n-alkanes, molecular simulation was employed to study the interaction between polyacrylate pour point depressants with different side chain length and n-hexadecane, and the interaction between polyacrylate pour point depressants with different polar building blocks and n-hexadecane. It was shown that during wax precipitation process, the mixed energy is low when the side chain length of acrylate is compatible with n-hexadecane. It is easier for polyacrylate to go into wax-crystal lattice, thus lowering crude oil pour point. The simulation for pour point depressants consisting of acrylate and other different polar building blocks demonstrated that the stronger the polarity of polar building block, the lower the interaction energy between polymer pour point depressant and n-hexadecane. At the same time, it is easier for polymers with polar building blocks to interact with n-alkanes. The polar building block can effectively inhibit wax-crystal growth and thus improve crude oil low-temperature fluidity.

Correlation of crude oils and oil components from reservoirs and source rocks using carbon isotopic compositions of individual n-alkanes in the Tazhong and Tabei Uplift of the Tarim Basin, China

Carbon isotopic compositions were determined by GC–IRMS for individual n-alkanes in crude oils and the free, adsorbed and inclusion oils recovered by sequential extraction from reservoir rocks in the Tazhong Uplift and Tahe oilfield in the Tabei Uplift of Tarim Basin as well as extracts of the Cambrian–Ordovician source rocks in the basin. The variations of the δ13C values of individual n-alkanes among the 15 oils from the Tazhong Uplift and among the 15 oils from the Triassic and Carboniferous sandstone reservoirs and the 21 oils from the Ordovician carbonate reservoirs in the Tahe oilfield demonstrate that these marine oils are derived from two end member source rocks. The major proportion of these marine oils is derived from the type A source rocks with low δ13C values while a minor proportion is derived from the type B source rocks with high δ13C values. Type A source rocks are within either the Cambrian–Lower Ordovician or the Middle–Upper Ordovician strata (not drilled so far) while type B source rocks are within the Cambrian–Lower Ordovician strata, as found in boreholes TD2 and Fang 1. In addition, the three oils from the Cretaceous sandstone reservoirs in the Tahe oilfield with exceptionally high Pr/Ph ratio and δ13C values of individual n-alkanes are derived, or mainly derived, from the Triassic–Jurassic terrigenous source rocks located in Quka Depression.The difference of the δ13C values of individual n-alkanes among the free, adsorbed and inclusion oils in the reservoir rocks and corresponding crude oils reflects source variation during the reservoir filling process. In general, the initial oil charge is derived from the type B source rocks with high δ13C values while the later oil charge is derived from the type A source rocks with low δ13C values.The δ13C values of individual n-alkanes do not simply correlate with the biomarker parameters for the marine oils in the Tazhong Uplift and Tahe oilfield, suggesting that molecular parameters alone are not adequate for reliable oil-source correlation for high maturity oils with complex mixing.

Phylogenetic diversity of microbial communities associated with the crude-oil, large-insoluble-particle and formation-water components of the reservoir fluid from a non-flooded high-temperature petroleum reservoir

The diversity of microbial communities associated with non-water-flooded high-temperature reservoir of the Niibori oilfield was characterized. Analysis of saturated hydrocarbons revealed that n-alkanes in crude oil from the reservoir were selectively depleted, suggesting that crude oil might be mildly biodegraded in the reservoir. To examine if any specific microorganism(s) preferentially attached to the crude oil or the other components (large insoluble particles and formation water) of the reservoir fluid, 16S rRNA gene clone libraries were constructed from each component of the reservoir fluid. The clones in the archaeal libraries (414 clones in total) represented 16 phylotypes, many of which were closely related to methanogens. The bacterial libraries (700 clones in total) were composed of 49 phylotypes belonging to one of 16 phylum-level groupings, with Firmicutes containing the greatest diversity of the phylotypes. In the crude-oil- and large-insoluble-particle-associated communities, a Methanosaeta-related phylotype dominated the archaeal sequences, whereas hydrogenotrophic methanogens occupied a major portion of sequences in the library of the formation-water-associated community. The crude-oil associated bacterial community showed the largest diversity, containing 35 phylotypes, 16 of which were not detected in the other bacterial communities. Thus, although the populations associated with the reservoir-fluid components largely shared common phylogenetic context, a specific fraction of microbial species preferentially attached to the crude oil and insoluble particles.

Distribution of high-molecular-weight n-alkanes in paraffinic crude oils and asphaltene-resin-paraffin deposits

Paraffinic and high-paraffin oils and asphaltene-resin-paraffin (ARP) deposits of Samara oblast have been investigated by differential scanning calorimetry (DSC) and GLC techniques. High-paraffin oils have been found to contain n-alkanes with the number of carbon atoms of C15-C60 and higher forming a crystalline phase with the mp ∼30–40°C. The ARP deposits from high-paraffin oils almost do not contain highmolecular-weight n-alkanes with the number of carbon atoms >55. This is due to the peculiarities of the crystallization and cocrystallization processes of high polydispersity n-alkanes in crude oils.

Compositional Characteristics and Geochemical Significance of N-alkanes in Process of Crude Oil Cracking

The simulation experiments with crude oil samples have been performed in laboratory by using high temperature simulative techniques, and the characteristics of change of compositions have also been analyzed by gcochemical methods in the cracking process. The results indicate that before a large number of gaseous hydrocarbons being generated by cracking of crude oil, the n-alkanes of high molecular weight from crude oil has already begun to be pyrolyzed, and C + 15 hydrocarbon mainly cracked into C 6–C 14. With increasing maturity, C 6–C 14 is further transformed into C 1–C 5, accompanied by the output of benzene, ultimately forming methane and cracking bitumen. In the pyrolysis of n-alkanes process, abundance of benzene and its homologue show significantly increasing, which can be used as potential distinguishing marks of crude oil cracking. Besides, comparative simulation experiments on n-hexadecane have been performed in laboratory by the same experimental condition, and it shows that the characteristics of change of compositions are basically the same as that of n-alkanes in crude oil.

Biomarkers and compound-specific stable carbon isotope of n-alkanes in crude oils from Eastern Llanos Basin, Colombia

Representative samples of crude oils from Cusiana, Cupiagua, Apiay, Castilla and Chichimene fields in the Eastern Llanos Basin of Colombia were analyzed to determine its compound-specific stable carbon isotope composition (CSIA) using gas chromatography–isotopic ratio–mass spectrometry (GC–IRMS). GC–IRMS analyses of n-alkanes allowed differentiating between Cretaceous and Cretaceous/Tertiary oil samples. Cretaceous sourced samples have δ13C-enriched values than Cretaceous/Tertiary sourced samples; the heavier isotope composition of these samples is due to their major terrigenous organic matter input. Their isotope distribution patterns suggest significant algal and/or bacterial contribution (marine origin). The analysis of the n-alkane fractions by GC–IRMS confirms that the organic matter has marine origin in those samples from Cusiana, Cupiagua and Apiay while Castilla and Chichimene have marine origin with terrestrial inputs. The results were confirmed by gas chromatography/FID and gas chromatography/mass spectrometry (GC/MS). Basic geochemical composition show that samples from Cupiagua/Cusiana fields and Apiay/Castilla/Chichimene fields in the Llanos basin, Colombia present different characteristics reflecting a specific for each depositional environment.

Organic-geochemical Differentiation of Petroleum-type Pollutants and Study of Their Fate in Danube Alluvial Sediments and Corresponding Water (Pančevo Oil Refinery, Serbia)

A review is given in this paper of the up-to-date results observed in differentiation and transformation studies on petroleum-type pollutants in underground and surface waters. Water and particulate matter derived from the locality of Pancevo Petroleum Refinery, Serbia (River Danube alluvial formations). It was shown that distributions of n-alkanes, steranes and triterpanes, and δ13CPDB values of n-alkanes may successfully be used for qualitatively differentiating the petroleum-type pollutants from native organic matter in recent sedimentary formations. In underground waters, a petroleum-type pollutant is exposed to microbiological degradation which is manifested through relatively fast degradation of n-alkanes. Following an almost complete degradation of crude oil n-alkanes in underground water, the biosynthesis of novel, even carbon-number C16–C30n-alkanes may be observed. It is shown that the n-alkane distribution observed in a petroleum-type pollutant may depend on the intensity of its previous interaction with water. The fate of petroleum-type pollutants in environmental waters may be predicted through laboratory simulative microbiological degradation experiments by using microorganism consortiums similar to those observed under relevant natural conditions, as well as on corresponding nutrient base.

A kinetic model for thermally induced hydrogen and carbon isotope fractionation of individual n-alkanes in crude oil

A quantitative kinetic model has been proposed to simulate the large D and 13C isotope enrichments observed in individual n-alkanes (C 13–C 21) during artificial thermal maturation of a North Sea crude oil under anhydrous, closed-system conditions. Under our experimental conditions, average n-alkane δ 13C values increase by ∼4‰ and δD values increase by ∼50‰ at an equivalent vitrinite reflectance value of 1.5%. While the observed 13C-enrichment shows no significant dependence on hydrocarbon chain length, thermally induced D-enrichment increases with increasing n-alkane carbon number. This differential fractionation effect is speculated to be due to the combined effect of the greater extent of thermal cracking of higher molecular weight, n-alkanes compared to lower molecular weight homologues, and the generation of isotopically lighter, lower molecular weight compounds. This carbon-number-linked hydrogen isotopic fractionation behavior could form the basis of a new maturity indicator to quantitatively assess the extent of oil cracking in petroleum reservoirs. Quantum mechanical calculations of the average change in enthalpy (ΔΔH ‡) and entropy (ΔΔS ‡) as a result of isotopic substitution in n-alkanes undergoing homolytic cleavage of C-C bonds lead to predictions of isotopic fractionation that agree quite well with our experimental results. For n-C 20 ( n-icosane), the changes in enthalpy are calculated to be ∼1340 J mol -1 (320 cal mol -1) and 230 J mol -1 (55 cal mol -1) for D-H and 13C- 12C, respectively. Because the enthalpy term associated with hydrogen isotope fractionation is approximately six times greater than that for carbon, variations in δD values for individual long-chain hydrocarbons provide a highly sensitive measure of the extent of thermal alteration experienced by the oil. Extrapolation of the kinetic model to typical geological heating conditions predicts significant enrichment in 13C and D for n-icosane at equivalent vitrinite reflectance values corresponding to the onset of thermal cracking of normal alkanes. The experimental and theoretical results of this study have significant implications for the use of compound-specific hydrogen isotope data in petroleum geochemical and paleoclimatological studies. However, there are many other geochemical processes that will significantly affect observed hydrogen isotopic compositions (e.g., biodegradation, water washing, isotopic exchange with water and minerals) that must also be taken into consideration.

Hydrogen isotopic compositions, distributions and source signals of individual n-alkanes for some typical crude oils in Lunnan Oilfield, Tarim Basin, NW China

Isotopic compositions of carbon-bound hydrogen in individual n-alkanes from several typical crude oil samples from Lunnan Oilfield, Tarim Basin, NW China, were firstly measured using newly developed gas chromatography-thermal conversion-isotope ratio mass spectrometry. The similar range of δ D of individual n -alkanes of crude oils among reservoirs of different geological times reflects that hydrocarbons are all derived from the same marine depositional environment. Compared to the theoretic value (-150‰) and the reported δ D values ( n C13― n C27, -160‰―-90‰) of individual n -alkanes for Ordovician-sourced crude oils in the Canadian Williston Basin, the hydrogen isotopic composition of individual n -alkanes in crude oils from Lunnan Oilfield is characterized by heavy hydrogen isotopic values ( n C12― n C27, -120‰―-60‰). In terms of the factors that control the fractionation of hydrogen isotopes, relatively saline depositional environment and higher thermal maturation were attributed to the heavy d D values of individual n-alkanes in crude oils from Lunnan Oilfield.

04/00108 The quantitation and origin of C 40+n-alkanes in crude oils and source rocks : Hong, Z. et al. Organic Geochemistry, 2003, 34, (7), 1037–1046

04/00108 The quantitation and origin of C 40+n-alkanes in crude oils and source rocks : Hong, Z. et al. Organic Geochemistry, 2003, 34, (7), 1037–1046