The influence of biodegradation on resins and asphaltenes in the Liaohe Basin

Asphaltenes are traditionally considered to be recalcitrant to microbial alteration. Resins and asphaltenes of seven biodegraded oils extracted from reservoir cores of two columns (Es3 and Es1) of the Lengdong oilfield in the Liaohe Basin, NE China, were studied to test this hypothesis. Elemental (C, H, N, O, S) and isotopic compositions (δ¹³C and δ¹⁵N) were measured, FT-IR was used to study the oxygenated functionalities of both resins and asphaltenes, and Py–GC–MS was used to elucidate how alkyl side chains of asphaltenes were altered during biodegradation. We conclude that the products of biodegradation, such as carboxylic acids, phenol and alcohols, may not only contribute to the resin fraction of crude oils, but also are linked with functionalities of resins and asphaltenes. The amount of asphaltenes increases because some resin molecules are enlarged and their polarity increased such that they can be precipitated by hexane as newly generated asphaltenes. Thus, the hydrocarbons that are progressively consumed during biodegradation can pull the δ¹³C of asphaltene fraction closer to the δ¹³C of the altered resins and hydrocarbons that were consumed.     

南堡凹陷原油高分辨质谱特征及其地球化学意义

南堡凹陷深部油气资源丰富, 油气成因研究薄弱.首次采用高分辨质谱(负离子电喷雾离子源(electrospray ionization, 简称ESI)傅里叶变换离子回旋共振质谱(Fourier transform ion cyclotron resonance mass spectrometry, 简称FT-ICR MS)技术对南堡凹陷原油中杂原子化合物的组成与分布特征及其地球化学意义进行了研究.应用负离子ESI FT-ICR MS检测出9种主要杂原子组合类型, 分别为N₁、N₁O₁、N₁O₂、N₁O₃、N₂、O₁、O₂、O₃和O₄类, 其中N₁、O₁和O₂类在所有样品中普遍存在且相对丰度较高.经研究发现成熟度对原油中N₁、O₁类化合物碳数分布、缩合度有明显的控制作用.实验观察到N₁类DBE(等效双键数)=12, 15的高低分子量同系物相对丰度参数C_16-20/C_21-50-DBE₁₂-N₁和C_20-24/C_25-50-DBE₁₅-N₁、N₁类缩合度参数DBE₁₂/DBE₉-N₁及O₁类缩合度参数DBE_8-9/DBE₄-O₁与成熟度指标Ts/Tm、TMNr具有良好的相关性, 认为它们可作为该区原油成熟度评价指标, 反映烃类演化的热动力学原理.南堡凹陷不同层系原油高分辨质谱特征有明显差异, 指示其可应用于母源岩性质识别.综合研究认为, FT-ICR MS在成熟度评价、油气成因与油源识别等方面地球化学意义显著, 其在油气地球化学理论研究和油气勘探中具有潜在的应用价值.      

A comparison of organosulphur compounds produced by pyrolysis of asphaltenes and those present in related crude oils and tar sands

Asphaltenes and NSO fractions from a variety of oils and tar sands have been characterized by pyrolysis-gas chromatography (Py---GC) using both flame ionization and flame photometric detectors. Organosulphur compounds were not always produced by pyrolysis of the asphaltenes isolated from the biodegraded tar sand extracts although pyrolysis of the NSO fractions produced a series of thiophenes from all of the samples examined. These observations suggest that under certain conditions, asphaltene fractions may be affected by biodegradation, leading to preferential removal of the sulphur containing compounds. In addition, it was observed that Py---GC of asphaltenes permitted oils to be differentiated on the basis of their source rock lithology. Oils derived from carbonate source rocks produced thiophene/benzothiopene ratios <1 whilst the same ratio was >1 for oils derived from shales. Thiophene/dibenzothiophene ratios could be used in a similar manner.     

东濮凹陷盐湖相原油氮/氧化合物分布特征及其应用

东濮凹陷盐湖相原油中杂原子化合物研究薄弱。采用高分辨率质谱技术、结合色谱-质谱,对东濮凹陷盐湖相、淡水湖相原油、烃源岩中的含氮、氧化合物进行了检测。结果表明,原油中含有丰富的氮、氧化合物, N₁、O₁和O₂占绝对优势;随成熟度增加,N₁和O₁类化合物相对丰度增加、O₂类化合物相对丰度降低、氮/氧化合物的缩合度增加、烷基侧链碳数范围降低,提出了多项氮、氧化合物的成熟度辅助识别指标,建立了DBE₁₅/DBE₉-N₁和DBE₁₅⁺/DBE₁₄^--N₁与折算镜质体反射率之间的定量关系式。通过对氮、氧化合物的油-油、油-岩对比,认为东濮凹陷盐湖相原油主要来自成熟烃源岩。基于高分辨率质谱的氮、氧化合物具有重要的成熟度评价、油源对比、油气运移示踪的应用前景。     

基于傅里叶变换质谱的烃源岩成熟度评价方法及地质意义

<正>伴随非常规油气资源的勘探开发,油气资源开采的广度和深度进一步扩大,一定程度上缓解了我国油气供需矛盾、保障了我国能源安全,同时有力推动了能源结构战略转型。但同时也对能源地质研究工作提出了新的挑战。有机质成熟度是油气评价的重要参数之一,不同成熟阶段的有机质会对应产出不同成因、不同性质、不同质量的油气,如何准确评价沉积有机质成熟度是当前油气资源勘探开发工作的关键问题之一。前人在科研实践工作中从光学、化学、谱学等角度提出了适用条件各异的成熟度评价方法,在部分地质环境中获得了良好的应用效果,但已有的成熟度指标多受测定方法原理的制约导致其适用性不同程度受限(肖贤明等,2020),制约了油气资源的高质量勘探开发。     

Characterisation of the non-asphaltene products of mild chemical degradation of asphaltenes

The major steranes of the non-asphaltene fraction of Nigerian tar sand bitumen (maltene) are the c₂₇-c₂₉ diasteranes [13β(H),17α(H); 20R + S] and C₂₈-C₂₉ regular steranes [14β (H),17β (H); 20S]. The reducing metal reaction products of the corresponding asphaltenes (maltene-I) contain mainly C₂₇-C₂₉ regular steranes with the 14β(H),17β(H); 20R + S and 14α(H),17α(H); 20R + S configurations as well as the corresponding diasteranes having the 13β(H),17α(H); 20R + S configuration. These sterane distributions suggest that maltene-I corresponds to an unaltered oil whilst the maltene is equivalent to the product of severe biodegradation of maltene-I. This is consistent with maltene-I being the remnant of “original oil” trapped within the asphaltene matrix and protected from the effect of in-reservior biodégradation.Degradation of Nigerian asphaltenes by refluxing with ferric chloride-acetic anhydride or methanolic potassium hydroxide also releases soluble reaction products having the characteristics of unaltered oil such as the presence of n-alkanes having an unbiased distribution. These methods appear to be milder and more suitable than reducing metal reactions for releasing hydrocarbons occluded by asphaltenes.     

烃源岩生成有机酸过程的高分辨质谱研究

研究石油中有机酸的生成过程对研究储层改造、石油润湿性及页岩油可动性评价具有重要意义。在热压生烃模拟实验基础上,对Ⅲ型烃源岩不同演化阶段生成油中的非烃馏分进行了负离子电喷雾傅立叶变换离子回旋共振质谱分析,研究了烃源岩生成有机酸过程。对样品生成有机酸分析表明,在整个演化过程烃源岩都能生成有机酸,在低演化阶段主要生成脂肪酸,随演化程度的升高,脂肪酸丰度快速减少,芳环酸开始大量生成。随演化程度的增加,芳环上短链取代基发生断裂,并促进了有机酸的缩合,使得生成的有机酸缩合度逐渐提高,高碳数有机酸逐渐减少;烃源岩生成脂肪酸系列中存在偶奇优势,生成的C16、C18脂肪酸存在异常高丰度, C16、C18脂肪酸异常丰度现象可能是污染造成的,是否与烃源岩类型及成熟度有关尚需进一步研究。     

A Matrix‐Matched Reference Material for Validating Petroleum Re‐Os Measurements

This study presents two matrix‐matched reference materials developed for petroleum Re‐Os measurements. We present the Re and Os mass fractions and ¹⁸⁷Re/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os values (ratio of the number of atoms of the isotopes) for repeatedly measured aliquots (ca. 120–150 mg test portions) of the NIST Research Material 8505 (RM 8505) crude oil, and its asphaltene and maltene fractions, and ~ 90 g of homogeneous asphaltene powder isolated from this oil. Measurements were performed using the Carius tube‐isotope dilution negative‐thermal ionisation mass spectrometry methodology. The RM 8505 crude oil contains 1.98 ± 0.07 ng g^?1 Re and 25.0 ± 1.1 pg g^?1 Os, with Re‐Os isotope amount ratios of 452 ± 6 for ¹⁸⁷Re/¹⁸⁸Os and 1.51 ± 0.01 for ¹⁸⁷Os/¹⁸⁸Os (n = 20, 95% conf.). The homogeneous asphaltene sample contains 16.52 ± 0.10 ng g^?1 Re and 166.0 ± 0.9 pg g^?1 total Os, and possesses isotope amount ratios of 574 ± 3 for ¹⁸⁷Re/¹⁸⁸Os and 1.64 ± 0.01 for ¹⁸⁷Os/¹⁸⁸Os (n = 24, 95% conf.). The intermediate precision of these data makes the RM 8505 whole oil and the (~ 90 g) homogenised asphaltene appropriate petroleum matrix‐matched reference materials for Re‐Os measurements. The asphaltene fraction of the oil is the main carrier of Re and Os of the RM 8505 whole oil, and caution is suggested in using asphaltene and maltene fractions of a single oil for Re‐Os geochronology.     

东濮凹陷北部盐湖相原油特征与成因

东濮凹陷盐湖相油气成因与成藏机理研究薄弱。采用色谱/质谱(GC/MS)等常规技术,结合傅立叶变换离子回旋共振质谱、单体烃碳同位素技术,对东濮凹陷北部文明寨、卫城地区油气特征及其成因进行了解剖。结果表明,该区原油具有植烷对姥鲛烷优势显著、伽马蜡烷富集、升藿烷“翘尾”、甾烷异构化程度较低等咸水、盐湖相原油的典型特征。原油还具有正构烷烃单体烃碳同位素呈低碳重、高碳轻、近两段式分布的特征,与柴达木盐湖相原油有所差异。原油中检测到丰富的S1、S2、O1S1、N1、O1、O2、O3等芳构化程度较低的NSO化合物,其与该区低熟油的形成关系密切。油-油、油-岩详细对比表明,东濮凹陷北部原油主要来自埋深超过3 000 m的沙三—沙四段烃源岩、存在不同成熟度原油混合聚集现象。研究结果对该区进一步油气勘探具有重要指示意义。     

Biodegradation preference for isomers of alkylated naphthalenes and benzothiophenes in marine sediment contaminated with crude oil

Contamination of coastal marine sediments with polycyclic aromatic hydrocarbons is pervasive, with major sources including anthropogenic activity and natural seepage. Biodegradation serves as a major hydrocarbon sink with evaporation and dissolution responsible for the removal of low boiling range compounds and photo-oxidation acting on many multi-substituted aromatic compounds. In this work, first-order rate constants for aerobic biodegradation were quantified for naphthalene (N), benzothiophene (BT) and their alkylated congeners (1-4 carbon substituents (C1-C4)) in laboratory experiments with oil laden marine sediments from a natural seep. Rate constants were used as proxies for microbial preference, which follows the order: naphthalene > C1N > C2N > C1BT > C2BT > benzothiophene > C3BT > C3N > C4BT > C4N, with some overlap. The application of comprehensive two dimensional gas chromatography further enabled separation and quantification of multiple structural isomers for C2N-C4N and C2BT-C4BT, with 7-12 isomers resolved for each C2N-C4N and 4-7 isomers resolved for each C2BT-C4BT. A strong isomeric biodegradation preference was noted within each of these compound classes, with rate constants varying as much as a factor of 2 for structural isomers of the same compound class. Each isomer was consumed to a low, but non-zero concentration, suggesting that their residual load in sediment may be proportional to the number of structural isomers originally present, in addition to the pattern and the number of alkyl substitutions. The simultaneous first-order biodegradation rates observed for 52 aromatic hydrocarbons resolved in this study, along with reference compounds such as n-alkanes, lends support to the concept of broad scale metabolic specificity during aerobic biodegradation of petroleum.     

Field-ionization mass spectrometry: application to geochemical analysis

The thiourea adduct, thiourea non-adduct and aromatic fractions from a series of Alberta oil sand bitumens have been subjected to field ionization mass spectrometric analyses. Field ionization mass spectra feature little fragmentation and the molecular weight distributions of compounds in the fractions are readily obtained. Using this method, the various acyclic and cyclic saturated hydrocarbons and the hydrocarbon and thiophenic aromatic materials may be distinguished by compound type and number of carbon atoms. The effect of biodegradation on crude oils is illustrated in the results from the series of oil sand bitumens and their asphaltene pyrolysis products. Field ionization mass spectrometry is potentially an important new analytical tool in organic geochemistry.     

用高分辨率质谱揭示塔中4油田原油成因机制

塔里木盆地塔中4油田位于塔中构造较高部位, 具有显著不同于周边原油的特征.采用高分辨率质谱、色谱-质谱等对原油成因进行了调查.GC/MS分析表明, 塔中4油田石炭系原油中链烷烃(指示未降解-轻度降解)极其发育, 同时检测到丰富的降解三环萜烷及25-降藿烷系列(指示强烈生物降解), 反映该区油气具有多期充注特征.高分辨率质谱分析显示, 塔中4油田原油中硫化物分布正常, 低等效双键数(DBE)硫化物不太发育, 天然气组成与碳同位素也未显示异常, 反映石炭系原油可能未受TSR作用影响.观察到塔中4油田原油中硫化物组成与分布特征多数与下奥陶统原油相近, 指示两者可能有一定成因联系.混源模拟实验显示, 下奥陶统原油混入可导致塔中4油田原油出现高芳香硫特征.地质地球化学综合研究认为, 塔中4油田原油中芳香硫异常与深源油气混合有关, 与TSR作用关系不明显.      

Multi-method characterization of DOM from the Turia river (Spain)

Water concentrates from Turia river (1.5 mg L⁻¹ total organic C) obtained by nanofiltration (membrane mass cut-off 90 Da) were fractioned by non-ionic Amberlite resins (DAX8 and XAD4) to afford three samples termed as hydrophobic acid (50%), transphilic acid (24%) and hydrophobic neutral (12%). If a nanofiltration membrane 270 Da mass cut-off is used then about 50% of dissolved organic matter is not retained. These three fractions were characterized by analytical and spectroscopic techniques (¹H NMR, MALDI–TOF-MS, ESI–API-MS, ESI–MS/MS). Overall, these data are compatible with the presence of oligosaccharides, oligopeptides and fatty acids as the main components of dissolved organic matter. Particularly revealing was the information from MALDI–TOF-MS and ESI–MS/MS where series of compounds differing in the number of hexose units were identified. The three fractions have many spectroscopic similarities and, particularly the hydrophobic and transphilic ones, are really almost identical. This similarity in the fraction composition shows that the conventional fractionation procedure is inefficient as a standard general method for separation of different compound types. The composition of dissolved organic matter was confirmed, and some individual organic compounds identified, by GC–MS analysis of the silylated derivatives obtained by reacting the fractions with a mixture of N,O-bis(trimethylsilyl)trifluoroacetamide with trimethylchlorosilane (10%). Thus, rather surprisingly, the dissolved organic matter of this natural raw water is predominantly composed of a relatively simple mixture of a few types of compounds with molecular weights well below 1100 Da (about six hexose units). These results, particularly the absence of detectable amounts of high molecular weight humic acids and low molecular weight phenolic compounds indicates that trihalomethanes formed in the water disinfection process by Cl₂ really derive from oligosaccharides and oligopeptides. Also, the data suggests alternative strategies to effect a more efficient fractionation of the dissolved organic matter.     

The effect of biodegradation on polycyclic aromatic hydrocarbons in reservoired oils from the Liaohe basin, NE China

The occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) has been studied in oil columns from the Liaohe basin, NE China, characterized by varied degrees of biodegradation. The Es3 oil column has undergone light to moderate biodegradation – ranging from levels 2 to 5 on the [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, NJ, p. 363] scale (abbreviated as ‘PM level’) – while the shallower Es1 column has undergone more severe biodegradation, ranging from PM level 5 to 8. Both columns show excellent vertical biodegradation gradients, with degree of biodegradation increasing with increasing depth toward the oil–water contact (OWC). The compositional gradients in the oil columns imply mass transport control on degradation rates, with degradation occurring primarily at the OWC. The diffusion of hydrocarbons to the OWC zone will be the ultimate control on the maximum degradation rate. The chemical composition and physical properties of the reservoired oils, and the ‘degradation sequence’ of chemical components are determined by mixing of fresh oil with biodegraded oil.The PAH concentrations and molecular distributions in the reservoired oils from these biodegraded columns show systematic changes with increasing degree of biodegradation. The C₃₊-alkylbenzenes are the first compounds to be depleted in the aromatic fraction. Concentrations of the C_0–5-alkylnaphthalenes and the C_0–3-alkylphenanthrenes decrease markedly during PM levels 3–5, while significant isomer variations occur at more advanced stages of biodegradation (>PM level 4).The degree of alkylation is a critical factor controlling the rate of biodegradation; in most cases the rate decreases with increasing number of alkyl substituents. However, we have observed that C₃-naphthalenes concentrations decrease faster than those of C₂-naphthalenes, and methylphenanthrenes concentrations decrease faster than that of phenanthrene. Demethylation of a substituted compound is inferred as a possible reaction in the biodegradation process.Differential degradation of specific alkylated isomers was observed in our sample set. The relative susceptibility of the individual dimethylnaphthalene, trimethylnaphthalene, tetramethylnaphthalene, pentamethylnaphthalene, methylphenanthrene, dimethylphenanthrene and trimethylphenanthrene isomers to biodegradation was determined. The C₂₀ and C₂₁ short side-chained triaromatic steroid hydrocarbons are degraded more readily than their C_26–28 long side-chained counterparts. The C_21–22-monoaromatic steroid hydrocarbons (MAS) appear to be more resistant to biodegradation than the C_27–29-MAS.Interestingly, the most thermally stable PAH isomers are more susceptible to biodegradation than less thermally stable isomers, suggesting that selectivity during biodegradation is not solely controlled by thermodynamic stability and that susceptibility to biodegradation may be related to stereochemical structure. Many commonly used aromatic hydrocarbon maturity parameters are no longer valid after biodegradation to PM level 4 although some ratios change later than others. The distribution of PAHs coupled with knowledge of their biodegradation characteristics constitutes a useful probe for the study of biodegradation processes and can provide insight into the mechanisms of biodegradation of reservoired oil.     

The isotopic composition of carbon in the Alberta oil sand

The carbon isotopic ratios obtained from Athabasca bitumen, asphaltene and maltene have the same value $\text{δ}{}^{13}\text{C}\text{= ?29.6}\text{per ml}$. The corresponding values in the Cold Lake deposits are ?30.6, ?30.0 and ?31.6 per ml. The ratios determined for methane collected from the oil sand and its fractions are about 15 per ml lower than the above values. It appears that the Athabasca and Cold Lake Reservoirs have similar histories.     

Study of the biodegradation levels of oils from the Orinoco Oil Belt (Junin area) using different biodegradation scales

This work presents a study of the molecular composition of the saturated and aromatic hydrocarbon fractions of crude oils from the Orinoco Oil Belt (Junín area) in the Eastern Venezuelan Basin, with the purpose of classifying these samples following two distinct biodegradation assessment schemes: the PM scale [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, New Jersey, p. 363] and the Manco scale [Larter, S., Huang, H., Adams, J., Bennett, B., Snowdon, L.R., 2012. A practical biodegradation scale for use in reservoir geochemical studies of biodegraded oils. Organic Geochemistry 45, 66–76]. Both scales agree on the presence of different levels of biodegradation for the analyzed oils, although they are based on different groups of compounds. The PM scale uses mainly compounds from the saturated hydrocarbon fractions (e.g., n-alkanes, acyclic isoprenoids, terpanes and steranes) as well as aromatic steroids. On the other hand, the Manco scale considers other compounds (e.g., alkyltoluenes, naphthalene, methylnaphthalene, phenanthrene, alkylphenanthrenes and methyldibenzothiophenes) not included in the PM biodegradation scale. Thus, the combined use of these two scales allows the determination of the level of biodegradation of both saturated and aromatic compound classes. Dibenzothiophene (DBT), which was not included for the Manco score determination, also shows variations in peak intensity when compared to C₄-alkylnaphthalenes, presumably associated with the process of biological alteration. The differences in the biodegradation levels observed in the present study may be attributed to variations in parameters that control biodegradation rates laterally across the study area or the existence of varying communities of microorganisms, among other possible factors.     

Organic geochemistry of Recent equatorial deltaic sediments

The organic matter of recent deltaic sediments cored in the Mahakam delta, East Kalimantan, has been studied before and after physical fractionation into sands >50 μm, silts 5–50 μm and clays <5 μm. Both the lipid and non-lipid components have been investigated.Weight, carbon and nitrogen fractionation budgets were used to define three types of samples, depending on coarse particle contributions to the total amount of organic matter: a = a first type with more than 50% of the O.M. in the coarse particles, high C/N ratios and O.M. content, b = an intermediary type with medium C/N ratios and O.M. content, each fraction having quite the same O.M. content, c = a third type with less than 5% of the whole O.M. in the sands and the lowest C/N ratios and O.M. content.Concerning the global organic characteristics of the fractions, a systematic increase of C/N ratios occurs when going from clays to sands; the finer the fraction is, the more nitrogenous the compounds are. This enrichment in nitrogen is related to a persistent high rate of hydrolysable material either for argillaceous organic matter-poor sediments or for the clay fractions of all types of samples. Conversely, the type (a) coarse sediments, in particular the sandy components were resistant to acid hydrolysis with burial.Concerning the geochemical markers signatures of granulometric fractions, the distribution patterns of n-alkanes and n-fatty acids are characterized by the predominance of high molecular weight compounds >C₂₂. Carbon preference index (CPI) values are higher in the sands and silts, reflecting their enrichment in continentally-derived vegetation debris. For type (c), the fractionation revealed markers of microbial activity within the clay fractions. For all types of samples, we observed an increase with burial of the n-alkane and n-fatty acid concentrations, particularly in the clay fractions, suggesting possibly a better preservation and/or affinity of lipids with the finest fractions.     

东濮凹陷原油含硫化合物的分布特征及其应用

东濮凹陷盐湖相原油中杂原子化合物研究薄弱。采用高分辨率质谱结合色谱-质谱技术,对东濮凹陷盐湖相、淡水湖相原油中的含硫化物进行了检测。结果表明,原油中含有丰富的含硫化合物,S1和O1S1占绝对优势,咸水相原油富含S1类、淡水相原油相对富集O1S1类,指示O1S1/S1具有原始沉积环境指示意义。东濮盐湖相原油中的硫化物富含碳数为C27-35、C40的化合物,与原油中丰富的甾类、藿烷类与β-胡萝卜类化合物碳数相吻合,指示菌藻类、色素类生源的重要贡献。随成熟度增加,硫化物缩合度增加、烷基侧链碳数范围降低,相关参数DBE6/DBE12-S1、DBE3+6/DBE12+15+18-S1等可用于辅助评价原油成熟度。东濮低熟油含有丰富的低热稳定性硫化物,指示富硫干酪根和/或富硫大分子低温降解是低熟油形成的重要机制之一。     

Effect of secondary oil migration distance on composition of acidic NSO compounds in crude oils determined by negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry

The acidic and neutral NSO compounds in a series of Duvernay-sourced oils in Canada, which are believed to have migrated extensively over relatively long distances such as along the Rimbey-Meadowbrook reef trends, were characterized by negative-ion electrospray (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Heteroatomic compounds were characterized according to their class (number of nitrogen, oxygen and sulfur heteroatoms), degree of aromaticity [rings plus double bonds (DBE)] and carbon number distribution. The N₁, N₁O₁, N₁O₂, N₁S₁, O₁ and O₂ classes were identified in Duvernay-sourced oils. With increasing migration distance, the relative abundance of O₂, N₁O₁ and N₁O₂ showed a significant decrease, while the O₁ class increased from < 10% to nearly 30% of the total. With increasing migration along the Rimbey-Meadowbrook reef trend, pyrrolic nitrogen compounds (N₁ class) shows an enrichment of alkylcarbazoles (DBE = 9) relative to alkylbenzocarbazoles (DBE = 12), and of higher homologous relative to the lower homologous. O₁ compounds show a relative enrichment of those with low DBE values. Additionally, the N₁O₁ and N₁S₁ compounds show a relative enrichment of those with high DBE values, and of higher homologues compared to the lower homologues, indicating great potential for developing new migration indices.     

Analytical problems in determining peptide nitrogen in the humic fractions of three Italian soils

Peptides were released from organic matter fractions of three Italian soils (humin, humic and fulvic acids), when the samples were hydrolyzed in Ba(ON)₂-saturated solution at 105°C for 2 hr. The peptides obtained were separated using electrophoresis and paper chromatography. The presence of polypeptides in the soil organic matter was indicated by: (1) their hydrolysis by pronase; (2) the amino acids released by 6 N HCl hydrolysis; (3) The comparison of i.r. spectra of humic fractions before and after hydrolysis with 6 N HCl.Attempts at isolating the native proteinaceous compounds using electrophoresis in polyacrylamide gel failed; additionally, our attempts to hydrolyze proteinaceous components enzymatically in unfractionated soil organic matter, as well as in its fractions, before and after methylation, with pepsin, papain and pronase, were unsuccessful. Pronase demonstrated a weak proteolytic activity only at very low substrate-enzyme ratios (20 : 1) in humic and fulvic fractions and in whole phyrophosphate extract. Deproteinated substrates treated with pronase also released free amino acids, suggesting autodigestion.In humin, humic and fulvic fractions we found a total amino acid content of 40–45%, 12–24% or 1–85, respectively. Amino acid recovery from single fractions was about 70–80% of the total content in the unfractionated soil.