Bicyclic Sesquiterpanes Research Articles

Organic geochemistry of Duckmantian (Pennsylvanian) coals from the Ruhr Basin, western Germany

The molecular composition of 58 Duckmantian Ruhr coals and adjacent sedimentary rocks has been analyzed using organic-geochemical investigations representing a maturity range from 0.74 to 0.98% vitrinite reflectance. In addition eight samples of higher maturity (1.46 to 3.55% vitrinite reflectance) were studied for comparison. The composition of coals depends primarily on plant input into the peat swamps, but also to a large extent on thermal maturity. Several maturity-related parameters have been applied in this study such as MPI, DMAI, and diverse hopanoid-based maturity ratios. Especially diamantane-based parameters proved to be excellent for characterizing high rank samples, whereas hopane- and phenanthrene-based parameters are well-suited for the lower maturity range.Various specific biomarkers reflect the composition of the Duckmantian coals concerning the floral differences and floral shift during the Westphalian. The dominating n-alkanes, hopanes, and bicyclic sesquiterpanes show only marginal differences and reveal a quite homogenous floral composition within the six coal seams. Tetracyclic diterpanes, as approved markers for modern as well as Paleozoic conifers and "pre-gymnosperms", have been identified in all six coal seams, but in low concentration (one order of magnitude lower than bicyclic sesquiterpanes). A slight increase of the tetracyclic diterpane ent-beyerane in the younger seams indicates an increase in abundance of "pre-gymnosperms" (cordaites) during the Duckmantian. Significantly increased proportions of diverse compounds like bicyclic sesquiterpanes (eudesmane) or tetracyclic terpanes clearly testify an origin from higher land plants. The major part of the Duckmantian coal swamps biomass with its vitrinite rich coals originated presumably from barks of arborescent lycopods. High concentrations of hopanes mirror the input of bacterial organic matter and a strong microbial reworking of the deposited terrestrial plant organic matter.

Application of Light Petroleum Biomarkers for Forensic Characterization and Source Identification of Spilled Light Refined Oils

Light petroleum biomarkers such as bicyclic sesquiterpanes and diamondoids are ubiquitous components of crude oils and ancient sediments, and are also widely found in intermediate petroleum distillates and many finished petroleum products. These compounds are relatively resistant to biodegradation and light-to-medium evaporation weathering, thus particularly useful in oil-source correlation and differentiation for those cases where the traditional tri- to pentacyclic biomarkers are absent. This work utilized sesquiterpanes and diamondoids for fingerprinting and identification of light oils spilled on water. The gas chromatography/flame ionization detection (GC/FID) analysis and distribution profiles of polycyclic aromatic hydrocarbon (PAHs) and conventional biomarkers suggest that the spilled oils are mixtures of mainly gasoline and light diesel type fuel. Since potential source oil candidates were not available, and a large part of the hydrocarbons in gasoline and diesel co-eluted in chromatographic analysis, it is a challenge to quantify the gasoline and diesel in spill samples. It has been known from previous studies that the bulk concentrations of C14 to C16 sesquiterpanes are in the range of approximately 6,000 to 9,000 μg/g for many light diesel fuels, while little or no sesquiterpanes were detected in gasoline, light kerosene and heavy-end lubricating oils. The target sesquiterpanes in the spilled oil samples were determined to be in quite high concentrations: approximately 4,000 μg/g oil. Therefore, it was estimated that these spilled oil samples consist of approximately half gasoline and half light diesel. To verify the estimation, spilled samples were simulated by mixing a fresh gasoline and a light diesel with a similar carbon range as the spilled oils. Results from comparison of GC/FID chromatograms of the spilled oils with the simulated spill samples are consistent with that obtained from sesquiterpane analysis.

Chemical Fingerprints of Alberta Oil Sands and Related Petroleum Products

Alberta oil sands are known to contain the world's largest reserves of bitumen. The rapid growth in their production could result in a significant environmental impact. Fingerprinting bitumen and petroleum products from the Alberta oil sands is essential in order to better understand the chemical compositions of oil sands, prepare for potential oil spills, and address the associated environmental problems. This study presents an integrated quantitative chemical characterization of Alberta oil sands bitumen and other related Alberta oils using gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The characterized target hydrocarbons include n-alkanes, unsubstituted polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues (APAHs), biomarker terpanes and steranes, bicyclic sesquiterpanes, and diamondoids. The chemical features of bitumen in oil sands are clearly distinguishable from those of most other conventional crude oils. The chemical fingerprints of diluted oil sands bitumen and Albian Heavy Synthetic crude were significantly altered by either the diluent blended with the former or the upgrading processing of crude bitumen in the latter. A chromatographic hump of unresolved complex mixtures (UCMs) eluting between n-C10 to n-C40 is pronounced and n-alkanes are nearly absent in bitumen extracted from oil sands. Alkylated naphthalenes account for only a small proportion of the total APAHs in Alberta oil sands extracts. The PAH compounds in oil sands extracts and diluted bitumen are dominated by alkylated homologues with the relative distribution of C0– < C1– < C2– < C3– for all five APAH series. Biomarker terpanes and cage-like adamantanes were determined in almost identical abundance and distribution profile in oil sands extracts and diluted crude bitumen, while biomarker steranes and bicyclic sesquiterpanes were removed to varying degrees by physical weathering or biodegradation.

Petroleum Hydrocarbon Biodegradation under Seasonal Freeze−Thaw Soil Temperature Regimes in Contaminated Soils from a Sub-Arctic Site

Several studies have shown that biostimulation in ex situ systems such as landfarms and biopiles can facilitate remediation of petroleum hydrocarbon contaminated soils at sub-Arctic sites during summers when temperatures are above freezing. In this study, we examine the biodegradation of semivolatile (F2: C10-C16) and nonvolatile (F3: C16-C34) petroleum hydrocarbons and microbial respiration and population dynamics at post- and presummer temperatures ranging from -5 to 14 °C. The studies were conducted in pilot-scale tanks with soils obtained from a historically contaminated sub-Arctic site in Resolution Island (RI), Canada. In aerobic, nutrient-amended, unsaturated soils, the F2 hydrocarbons decreased by 32% during the seasonal freeze-thaw phase where soils were cooled from 2 to -5 °C at a freezing rate of -0.12 °C d(-1) and then thawed from -5 to 4 °C at a thawing rate of +0.16 °C d(-1). In the unamended (control) tank, the F2 fraction only decreased by 14% during the same period. Biodegradation of individual hydrocarbon compounds in the nutrient-amended soils was also confirmed by comparing their abundance over time to that of the conserved diesel biomarker, bicyclic sesquiterpanes (BS). During this period, microbial respiration was observed, even at subzero temperatures when unfrozen liquid water was detected during the freeze-thaw period. An increase in culturable heterotrophs and 16S rDNA copy numbers was noted during the freezing phase, and the (14)C-hexadecane mineralization in soil samples obtained from the nutrient-amended tank steadily increased. Hydrocarbon degrading bacterial populations identified as Corynebacterineae- and Alkanindiges-related strains emerged during the freezing and thawing phases, respectively, indicating there were temperature-based microbial community shifts.

Characteristics of bicyclic sesquiterpanes in crude oils and petroleum products

This study presents a quantitative gas chromatography–mass spectrometry analysis of bicyclic sesquiterpanes (BSs) in numerous crude oils and refined petroleum products including light and mid-range distillate fuels, residual fuels, and lubricating oils collected from various sources. Ten commonly recognized bicyclic sesquiterpanes were determined in all the studied crude oils and diesel range fuels with principal dominance of BS3 (C 15H 28), BS5 (C 15H 28) and BS10 (C 16H 30), while they were generally not detected or in trace in light fuel oils like gasoline and kerosene and most lubricating oils. Laboratory distillation of crude oils demonstrated that sesquiterpanes were highly enriched in the medium distillation fractions of ∼180 to 481 °C and were generally absent or very low in the light distillation fraction (boiling point to ∼180 °C) and the heavy residual fraction (>481 °C). The effect of evaporative weathering on a series of diagnostic ratios of sesquiterpanes, n-alkanes, and biomarkers was evaluated with two suites of weathered oil samples. The change of abundance of sesquiterpanes was used to determine the extent of weathering of artificially evaporated crude oils and diesel. In addition to the pentacyclic biomarker C 29 and C 30 αβ-hopane, C 15 and C 16 sesquiterpanes might be alternative internal marker compounds to provide a direct way to estimate the depletion of oils, particularly diesels, in oil spill investigations. These findings may offer potential applications for both oil identification and oil-source correlation in cases where the tri- to pentacyclic biomarkers are absent due to refining or environmental weathering of oils.

APPLICATION OF STATISTICAL ANALYSIS IN THE SELECTION OF DIAGNOSTIC RATIOS FOR FORENSIC IDENTIFICATION OF AN OIL SPILL SOURCE

ABSTRACT In this work, 14 fresh crude oils of different types and origins were analyzed by gas chromatography with mass-selective detection, and over 80 potentially diagnostic ratios were calculated based on the quantitation of isoprenoids, polycyclic aromatic hydrocarbons (PAHs), biomarkers, diamondoids, bicyclic sesquiterpanes and aromatic steranes, etc. Diagnostic power (DP) was calculated for the selection of the candidate source-sensitive diagnostic ratios and used to determine which ratios were most diagnostic among the crude oils studied. In order to investigate the effect of evaporative and biodegradative weathering on diagnostic ratios and thereby to differentiate weathering-resistant ratios from weathering-sensitive ratios, triplicate analyses were performed for two suites of reference oils, laboratory-evaporated Prudhoe Bay crude oils and laboratory-biodegraded Alberta Sweet Mixed Blend (ASMB) crude oils, respectively. Student'S t-test was used to statistically evaluate whether diagnostic ratios were significantly affected by weathering and to ensure that the observed change is not due to analytical variance. It was found that, diagnostic ratios generally remained consistent for oils with slight to medium evaporative weathering, only the ratios of those compounds with lower boiling points such as adamantanes changed greatly. For biodegraded oils, most of diagnostic ratios remained constant for lightly to moderately biodegraded oils; while most of diagnostic ratios with exception of certain triaromatic steranes and high-molecular-weight terpane and sterane biomarkers demonstrated significant changes for heavily biodegraded oils.

HIGHER PLANT BIOMARKERS IN PALEOGENE CRUDE OILS FROM THE YUFUTSU OIL‐AND GASFIELD AND OFFSHORE WILDCATS, JAPAN

Geochemical investigation of Paleogene oils from the onshore Yufutsu oil‐ and gasfield, southern Hokkaido, and from two nearby offshore wells, revealed the presence of numerous biomarkers of higher plant origin. Biomarkers in the oils belong to different groups of both angiosperm and gymnosperm origin; they include bicyclic sesquiterpanes, diterpanes, and triterpanes and their aromatized counterparts, which suggests a terrestrial origin for the oils. The oils were characterized as having a high wax content, a low content of organosulphur compounds, a high pristane/phytane ratio, and a low C27/(C27+C29) sterane ratio.Although the oils from on‐ and offshore Southern Hokkaido are similar in their geochemical composition, notable differences were observed in the biomarker signature of both saturate and aromatic fractions. The oils from the offshore wells appeared to have a greater abundance of higher plant biomarkers compared to those from the Yufutsu field, suggesting an enrichment in higher plant components. Differences in biomarker fingerprint could not be linked to the maturity effect, since the oils appeared to be of similar maturity levels, corresponding to the late stage of the oil window (0.9–1.2%, Rc). The differences in the biomarker signatures between the oils from the Yufutsu field and the offshore wells are likely to be due to facies variations in source organic matter, resulting from differences in the quantity and quality of land plant input.

Characterization, Weathering, and Application of Sesquiterpanes to Source Identification of Spilled Lighter Petroleum Products

Biomarkers have become increasingly important for identifying the source of spilled oil, due to their specificity and high resistance to biodegradation. The biomarkers most commonly used in forensic investigations are the high molecular weight (MW) tri- and pentacyclic terpanes and steranes. For lighter petroleum products such as jet fuels and diesels, the refining processes remove most high MW biomarkers from the original crude oil feedstock. The smaller bicyclic sesquiterpanes, however, are concentrated in these products. Sesquiterpanes are ubiquitous components of crude oils and ancient sediments. Examination of GC-MS chromatograms of these bicyclic biomarkers using their characteristic fragment ions (m/z 123, 179, 193, and 207) provides a highly diagnostic means for identifying spilled oil, particularly for lighter refined product samples that are difficult to identify by current techniques. In this work, sesquiterpanes in crude oils and petroleum products are identified and characterized, distributions of sesquiterpanes in oils and refined products are compared, the effects of evaporative weathering on sesquiterpane distributions are examined, and a methodology using diagnostic indices of sesquiterpanes is developed for oil correlation and differentiation. Finally, two case studies are presented to illustrate the unique utility of sesquiterpanes for fingerprinting and identifying unknown diesel spills.

Middle Distillate Fuel Fingerprinting Using Drimane-Based Bicyclic Sesquiterpanes

Petroleum biomarkers are ubiquitous hydrocarbons that occur in crude oils and are derived from formerly living organisms whose organic materials gave rise to the crude oil over geologic time. Biomarkers' specificity and resistance to weathering renders them useful in chemical fingerprinting of petroleum contamination in the environment. The biomarkers most commonly used in forensic issues, viz., tri- and penta-cyclic triterpanes and regular or rearranged steranes, are too high boiling for use in fingerprinting middle distillate petroleum products. The present article describes a suite of “low boiling” biomarkers (i.e., drimane-based bicyclic sesquiterpanes) that boil within the distillate fuel range (n-C13 to n-C16; ∼ 240°C to 285°C). GC/MS analysis of 24 dispensed (fresh) distillate fuels (Jet A, JP-5, and diesel fuel/fuel oil #2) demonstrate the specificity of sesquiterpane patterns in fuels of different origins. Analysis of fresh diesel fuel #2 and its associated, variably weathered NAPLs demonstrate the stability of the sesquiterpane despite complete biodegradation of n-alkanes. Finally, a case study of a forensic investigation is presented in which the sesquiterpanes are used to further unravel the sources of weathered diesel fuel/fuel oil #2 impacting soils on adjacent properties. Sesquiterpanes were used to demonstrate that the soils from the plaintiff's and defendant's properties contained distinct diesel fuel/fuel oil #2, which implied distinct sources and thereby led to a rapid settlement of the case.

Identification of Bicyclic Sesquiterpanes in Oils from the Niger Delta, Nigeria

Identification of Bicyclic Sesquiterpanes in Oils from the Niger Delta, Nigeria

Composition of the extract from a Carboniferous bituminous coal: 1. Bulk and molecular constitution

A procedure for the extraction, separation and characterization of coal bitumen is described. A Carboniferous coal was subjected to exhaustive (single-step) extraction with dimethylacetamide (DMAA) at ambient temperature. The treatment solubilized ∼24 wt% of the organic matter. The bitumen was fractionated further and some fractions were separated into normal and branched/cyclic components. By g.c. and g.c.-m.s., n-alkanes, hopanes, benzohopanes, steranes, bicyclic sesquiterpanes, seco-hopanes, polycyclic aromatic hydrocarbons, and their alkylated homologues were identified. Number-average structural analysis was applied to the polar fractions and revealed some peculiarities of the structural units, i.e. simple molecular aggregates.

Tricyclic terpanes in Precambrian bituminous sandstone from the eastern Yanshan region, North China

A bituminous sandstone at the base of the Xiamaling Formation (Precambrian) is a fossil oil pool which was thermally altered into reservoir bitumen ∼760 Ma ago. This reservoir bitumen was extracted, fractionated and analyzed for biomarkers. A novel series of extended tricyclic terpanes (C 18C 23) with a 13α( n-alkyl)-side chain configuration was identified by co-injection of two standards (C 18, C 20) and GC-MS analysis. Some bicyclic sesquiterpanes, C 18-norditerpanes, regular extended tricyclic terpanes (C 18C 24, no C 22), and alkylcyclohexanes were also detected. The source of the organic matter, its alteration in the sandstone reservoir and the origin of its novel tricyclic terpanes are all inferred to be microbial.

Geochemical characteristics of oils from Taiwan

Geochemical studies on a number of oils from Taiwan have shown that they are sourced predominantly from terrigenous organic matter. Biomarker characteristics include the presence of high amounts of long-chain regular isoprenoids, bicyclic sesquiterpanes, diterpanes, low concentrations or absence of tricyclic terpanes, presence of several C 24 tetracyclic terpanes and some source-specific pentacyclic terpanes and a predominance of C 29 steranes. For most of the oils, the n-alkanes extended to C 30 or above and have CPI values of approximately 1, indicating the mature nature of these oils. The pristane/phytane ratios, generally in excess of 5, suggest the likely prevalence of a highly oxic, nearshore, marine-open peat swamp depositional environment which incorporated large amounts of terrigenous organic matter. The long-chain isoprenoids extending to C 42, and possible higher, are proposed to be regular head-to-tail isoprenoids possibly derived from polyprenols in higher plants. The sesquiterpanes present in the oils range from C 15 and C 17 and are dominated by 8β(H)-drimane and 8β (H)-homodrimane. The diterpanes include C 17-C 20 tricyclic and C 19 and C 20 tetracyclic diterpanes. The presence of diterpanes in these oils suggests that resins derived from conifers contributed to the source of these oils. At least nine tetracyclic terpanes with carbon numbers ranging 24 to 27 were detected in Taiwan oils. Two series of tetracyclic terpanes are apparent, one is the de-A-oleanane/ursane series and the other is the 17,21-secohopane series. The former is more source-specific than the latter and is probably related to the presence of oleanane. A number of pentacyclic terpanes, including oleanane, have been detected and many of these compounds may be of terrigenous origin and source-specific. Oleanane, de-A-oleanane/ursane and de-A-lupane can be used as indicators for angiosperms which have evolved since the late Cretaceous. Sterane distributions in the Taiwan oils are dominated by the C 29 steranes and include regular and rearranged steranes, indicating the terrigenous nature of the organic matter in the source rocks. The significance of the variations observed in the biomarker distributions of the oils from Taiwan is discussed in some detail in this paper.

Biomarker distributions in crude oils and source rocks from different sedimentary environments

The saturated and aromatic hydrocarbons from a significant number of oils and source rocks derived from terrestrial and marine organic matter have been analysed by GC and GC-MS. Results show that certain classes of biomarkers including bicyclic sesquiterpanes, tricyclic terpanes, pregnanes, methylsteranes, rearranged steranes, hopane sulfides, benzohopanes, long-chain alkylbenzenes and pentacyclic triterpanes can be used to distinguish differences in source input and/or depositional environments. Variations in the distributions of the naphthalenes, phenanthrenes, fluorenes, dibenzofurans, dibenzothiophenes, naphthobenzothiophenes and triaromatic steroid hydrocarbons may also reflect disparities in source input or sedimentary environments.

Application of sesquiterpanes to the study of oil-gas source—the gas-rock correlation in the Qiongdongnan Basin

There are abundant sesquiterpane compounds in terrestrial source rocks and oils. During the thermal evolution, the relative concentration of bicyclic terpanes (C 14) decreases with increasing maturation of organic matters. The concentrations of drimane and homo-drimane increase owing to the dehydroxylation and chemo-dynamics of precursors. Their sharp changes begin around the threshold. The lower the maturity, the more obvious the predominance of homo-drimanes. The crude oils in the Ya13-1 gas field, Qiongdongnan Basin, belong to condensate oils. The “counting vitrinite reflectances” range from 0.8 to 1.10%. The maturity indices, such as paraffin index and hopane value, show that the condensate oils are low mature, which are possibly generated from the resin matter of higher plants at lower temperatures. The aromatic contents of Ya13-1 condensate oils amount to 50%. The Pr/Ph ratios are between 6 and 10. It is shown that the oils are an aromatic base coal generated from coal-bearing strata. The main source rocks for the gas field are the coal-bearing Yacheng Formation (E) based on the oil-rock correlation by bicyclic terpanes. Condensate oil, especially with bicyclic sesquiterpanes, is of importance for the gas-rock correlation, which expands the application range of biomarkers in petroleum exploration.

Characteristics of biomarkers in the Recent sediment from Qinghai Lake, northwest China

The occurrence of biomarker hydrocarbons in the Recent sediment of Qinghai Lake was investigated. It was found that the distribution of these biomarkers in Qinghai Lake, a semi-saline water lake, is unusual. The distribution of n-alkanes is predominated by high carbon-numbered alkanes with a high OEP (CPI) value. Two series of bicyclic sesquiterpanes derived from micro-organisms, e.g. algae or bacteria, were detected. The occurrence of tricyclic and tetracyclic terpenoids is characterized by the input of the organic matter from aquatic organisms. The conversion from hopenes existing in bacteria and blue-green algae into hopanes is put forward in this paper. C 27C 29 regular steranes, 4-methylsteroids, diasteranes, pregnanes, norsteroids and secosteranes were found in abundance in the sedimentary samples. Another important contribution of this paper is towards the geochemistry of amino acids in the Recent sediment of Qinghai Lake. The composition, distribution and evolution of the amino acids in the lacustrine sediments will be discussed in detail. It was found that several ratios of different amino acids have a clear diagenesis trend in the two cores studied. The racemization reaction of amino acids and their application in the geochemistry will also be discussed. The racemization of alanine and leucine were employed in this study to calculate the age of the sediment samples, with satisfactory result.

Geochemical characteristics of crude oils from the Cuyo Basin, Argentina

Crude oils from the Triassic Cuyo Basin are thought to be derived from a fresh-water lacustrine source rock, mainly the Upper Triassic organic-rich shales of Cacheuta Fm. By means of GC and GC-MS methods, the oils were analysed for characteristic compounds which may reflect biological input to the source sediments and maturity variations. Pristane/phytane ratios, distributions of n-alkanes, and the presence of significant amounts of bacteriohopanoid-derived compounds (hopanes, 8,14-secohopanes, 8,14-monoaromatic secohopanoids, benzohopanes) together with bicyclic sesquiterpanes in all the samples studied, are taken as an indication of possible reworking of algal organic matter by bacteria. Sterane distributions were consistent with a lacustrine origin of the oils. The occurrence of selected alkylnaphthalene derivatives as dominant compounds in the aromatic hydrocarbon fractions was a matter of special attention in the study. The variation of their concentrations with the maturity of the oils is compared to that of monoaromatic 8,14-secohopanoids. The results suggest that 1,2,5-trimethylnaphthalene in these oils is a product of hopanoid degradation under mild thermal conditions.