Steroid Hydrocarbons Research Articles

Dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum

The steroidal alkanes of a selection of sediments and oils have been examined by GC-MS with multiple metastable reaction monitoring. Specific 4-methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates. An immature marine oil shale and two mature marine oils of Triassic to early Cretaceous age contained high concentrations of C30 steranes comprising desmethyl, 24-ethyl-4α-methylcholestane and 4α,23,24-trimethylcholestane (dinosterane) isomers. An immature non-marine oil shale and two non-marine oils of Cretaceous to Eocene age contained stereoisomers of 24-ethyl-4α-methylcholestane as the dominant C30 steranes. Reaction monitoring analyses in GC-MS are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks.

長岡周辺新第三系ガス田の生物指標化合物

Cuttings materials from Katagai Gas Field in the vicinity of Nagaoka City, Niigata Prefecture, were analyzed for biological markers (triterpenoid and steroid hydrocarbons) in order to evaluate their validity as maturity indicies, with the following results.(1) Isomerization of both steranes and triterpanes are recognized from immature to oil generation zone.(2) The most reliable criteria in the immature zone and the oil generation zone are inferred to be the isomerization of hopane nucleus and the epimerization of stigmastane side chain, respectively.(3) Change of monoaromatic steroid hydrocarbons into triaromatics seems to occur from the immature to oil generation zone.(4) Cracking reactions in the side chains of C26, 27, 28-triaromatic steroid hydrocarbons into C20, 21-triaromatics appear to take place from the late stage of oil generation zone to the overmature zone. This reaction may be useful as a maturity index of crude oils or gas condensates, which cannot be measured for vitrinite reflectance.

Steroidal hydrocarbons of the Kishenehn Formation, northwest Montana

The Oligocene Kishenehn Formation of northwest Montana and southeast British Columbia consists of fluvial and lacustrine sediments (marlstones, lignites and oil shales) deposited in an elongate, intermontane half-graben. The petroleum source rock potential and steroidal hydrocarbon distribution of selected shales of the Kishenehn Formation were examined. Several steroidal hydrocarbon series were documented, including 4-desmethylsteranes, 4-methylsteranes, sterenes, diasterenes, spirosterenes, C-ring monoaromatic steroids and B-ring monoaromatic anthrasteroids. Non-steroid hydrocarbons present include hopenes, ββ-hopanes, moretanes, perylene, botrycoccane, a series of alkylcyclohexanes, and a fused-ring aromatic tentatively identified as a tetrahydrochrysene. Source rock analysis indicates that the Kishenehn Formation possesses excellent petroleum source potential. Conventional thermal maturity parameters (vitrinite reflectance and Rock-Eval T max values), as well as maturity parameters derived from molecular parameers ( n-alkane, steroid and hopanoid distributions) suggest that much of the Kishenehn Formation is currently undergoing organic diagenesis. Typical molecular indicators of thermal immaturity include the occurrence of high relative amounts of: (a) 5β(H) desmethylsteranes; (b) 14α(H) B-ring monoaromatic anthrasteroids; and (c) 4β(CH3) methylsteranes. A near-shore freshwater lacustrine depositional environment is indicated, with some input of terrigenous organic matter (high-CPI C23–C31 n-alkanes and relatively high ethylcholestane content), while the presence of 4-methylsteroids and botryococcane indicate significant contributions from dinoflagellates and Botryococcus braunii. The occurrence in the Kishenehn Formation of a diverse selection of 4-methyl and 4-desmethyl aliphatic and aromatic steroids provides a unique opportunity to monitor co-variance of molecular maturity indicators in sediments depositedunder relatively constant depositional conditions.

Geochemical Study of Oils, Source Rocks, and Tar Sands in Pauls Valley Area, Anadarko Basin, Oklahoma: ABSTRACT

An organic geochemical study of numerous oils and source rocks from the Anadarko basin has been undertaken in an attempt to determine the number of genetically related families of oils in the Pauls Valley area of the Anadarko basin, in addition to determining the potential source rocks for these oils. In the study area it was found that, of the oils examined, there were basically two families of oils. The majority of oils examined from the Oil Creek, Bromide, Hunton, and other sands appeared to have a similar source which appeared to be the Woodford Shale. A smaller and distinct group of oils appeared to be source and reservoired in the Viola Limestone. The correlations were made by determination of the various classes of biomarkers in the oils and source rock extract. The compounds examined included n-alkanes, isoprenoids, steranes, hopanes, and monoaromatic steroid hydrocarbons. The distributions of these compounds will be discussed in addition to the way in which the data are used to make the above-mentioned correlations. In the course of this study, a number of tar-sand samples in Upper Mississippian tar sands from Carter County, Oklahoma, were also examined in some detail. These samples were of particular interestmore » since they presented an opportunity to study samples that had been biodegraded to differing degrees. Hence several classes of biomarkers, namely alkanes, steranes, hopanes, mono and tri-aromatic steranes, and porphyrins, were analyzed from these different tar sands. The aims of the study were two-fold, with the first being to study the in-situ effects of progressive biodegradation on a series of samples derived from the same source. The second was to determine the origin of the oil responsible for the tar sands.« less

Effects of thermal maturation on steroid hydrocarbons as determined by hydrous pyrolysis of Phosphoria Retort Shale

Hydrous pyrolysis experiments on the Phosphoria Retort Shale generate bitumen extracts and expelled oils that have steroid hydrocarbons with m/z 217-, 231-, and 253-mass Chromatographic distributions that are similar to those of bitumens and crude oils in the natural system. These experiments agree with the natural observations that diasteroid hydrocarbons increase relative to their regular counterparts with increasing thermal stress, while their C 27 through C 29 proportionality shows a slight enrichment in C 27. Relative concentrations of 20S to 20R configurations of 24-ethyl-14α,17α-cholestane show the expected increase with increasing thermal stress into the early part of the primary oil generation stage, but thereafter decrease with increasing thermal stress. If this reversal is found in high maturity sections of the natural system, the utility of this transformation as a maturity index will be limited. Triaromatic- to monoaromatic-steroid hydrocarbon concentrations increase with increasing thermal stress as observed in the natural system. Preferred migration of monoaromatic steroid hydrocarbons from bitumen extracts to expelled oils places considerable doubt on currently employed kinetic models for this aromatization reaction. As in the natural system, the experiments show relative concentrations of low-molecular weight- to high-molecular weight-triaromatic steroid hydrocarbons to increase with increasing thermal stress. Assuming a first-order reaction rate, the apparent activation energy and pre-exponential factor for this apparent side-chain cleavage reaction are 175.59 kJ mol −1 and 2.82 × 10 13 hr −1, respectively. These kinetic parameters are geologically reasonable and are similar to those for the overall generation of expelled oil.

Structure and significance of a novel rearranged monoaromatic steroid hydrocarbon in petroleum

Abstract A monoaromatic steroid hydrocarbon isolated from a catalytic dehydrogenation/isomerization mixture derived from 5α-cholestane was determined to be a (10β→ 5β) CH 3 -rearranged monoaromatic steroid (2a) by 1 HNMR analysis. Gas chromatography-mass spectrometry (GCMS) coinjection with a crude oil monoaromatic fraction and GCMS elution patterns suggest that this 5β-Me rearranged monoaromatic steroid is part of a series of C 27 -C 29 homologues in 20S and 20R pairs (2a-f) which are found in nearly all crude oils. Evidence from a study of Toarcian sediments from West Germany shows that the relative amounts of rearranged (2a-f) compared to regular (1a-1) C-ring monoaromatic steroids depends upon the strength of the anoxic environment during sedimentation. In addition, observation of rearranged/regular MA-steroid ratios in a suite of Jurassic oils demonstrates the differential effects of maturation on the preservation of the two series of biomarker compounds.

The origin and fate of 4-methyl steroid hydrocarbons. I. Diagenesis of 4-methyl sterenes

Abstract Treatment of 4-methylcholest-4-ene under mild acid conditions at low temperatures gives chemical evidence for certain features seen in the distributions of sedimentary 4-methyl steroid hydrocarbons, and further indicates that many low temperature diagenetic reactions of steroids are explicable in terms of acid catalysed rearrangements. Specifically, the results provide: (i) Indirect evidence that the 4-ene skeleton is a key intermediate in the dehydration of 4-methyl stanols in sediments. (ii) An explanation for the distribution of 4-methyl sterenes and A-nor sterenes in the lacustrine Messel shale (Eocene). (iii) An explanation for the presence of 4β-methyl steranes in relatively immature sedimentary rocks, despite the precursor stanols having the 4α-methyl configuration. With increasing maturity in the Paris Basin shales (Lower Toarcian), the less stable 4β-methyl steranes decrease gradually in abundance relative to their 4α-methyl counterparts, at a rate fairly similar to the change in pristane stereochemistry.

Steranes as indicators of petroleum-like hydrocarbons in marine surface sediments

Combined gas chromatography-mass spectrometry (GC-MS) can be used to reveal the distribution of triterpenoidal and steroidal hydrocarbons in petroleums. Commonly this is achieved by monitoring the ions m/z 191 and m/z 217. This technique, much used for oil-oil correlations, has also been proposed to be useful for the detection and ‘fingerprinting’ of petroleum-type hydrocarbons in contaminated surface sediments, although few examples appear to have been published. GC-MS of saturated hydrocarbon fractions isolated from a large number of sites in and around Sullom Voe, Shetland Islands shows that in some cases both biologically-derived and petroleum type components are distinguishable in the m/z 191 ‘fingerprints’. In contrast, the corresponding m/z 217 sterane ‘fingerprints’ are not complicated by biologically-derived steranes and even though the ratio of the major triterpanes to steranes exceeds 50:1 in some cases, the m/z 217 profile still yields a useful petroleum ‘fingerprint’.

Distribution of aromatic steroids in geological samples: their evaluation as geochemical parameters

The distribution of ring-C monoaromatic and triaromatic steroid hydrocarbons of about fifty crude oils and sediments of various origins and ages were studied in order to test their validity as geochemical source and maturity parameters. Three ratios appeared to be useful maturity parameters, i.e. A/B cis to trans isomers in non-rearranged monoaromatics, mono/triaromatics and shortvs long-chain homologues. Four other variations may be considered as source parameters depending upon lithology or other palaeo-environmental conditions, i.e. rearranged vs non-rearranged monoaromatics, 5β/5α -methyl rearranged monoaromatics, carbon number distribution and occurrence of a yet unknown series of methylated triaromatic steroids. 5α-Methyl rearranged monoaromatics seem to be particularly important in anhydrites from sabkha environments. Recent identification of most aromatic steroid constituents occurring in geological samples confers on this class of compounds an increasing value as correlation parameters in geochemical studies.

Biodegradation in South Texas Eocene oils — Effects on aromatics and biomarkers

The Eocene oil producing trend in South Texas provides an excellent area for studying sequential effects of biodegradation on crude oil composition. Many small fields contain oils of a common genetic type which exhibit a broad range of biodegration stages. Gas chromatograms of 26 oils from Eocene Jackson reservoirs in Duval County, Texas, show that n-paraffins are missing in 23 oils, while the other three appear to be undegraded. Among the degraded samples, a progressive increase in degradation is indicated by first a gradual disappearance of isoprenoids, then by disappearance of other prominent peaks in the C 13–C 17 range. Gas chromatography-mass spectrometry analyses were on nine oils, selected on the basis of their gas chromatograms to represent various biodegradation stages. Changes in distributions of geochemically important compound types, including the more common biomarkers, were related to extent of biodegradation. Significant observations include: (1) two- and three-ring aromatics, including benzo- and dibenzothiophenes show selectivity in degradation and disappear during adjacent degradation stages; (2) a series of adamantanes is unaffected; (3) steranes and aromatized steroid hydrocarbons remain undegraded; (4) tricyclic and tetracyclic terpanes are not degraded, but ammong pentacyclic triterpanes, a a slight decrease in C 29 and C 30 hopanes can be seen; and (5) bicyclic and diterpanes are degraded irregularly and less rapidly than aromatics. Aside from an early loss of straight-chain and branched-chain paraffins, biodegradation may follow quite different routes at different locations, particularly with regard to aromatics. Therefore, criteria for correlating biodegraded oils and assessing biodegradation stages on the basis of aromatic hydrocarbon distributions must be carefully selected.

Geochemical correlation of surface and subsurface oils, western Greece

Biodegraded seep oils, devoid of n-alkanes and most isoprenoid hydrocarbons, were successfully correlated with subsurface crude oils in western Greece primarily using carbon isotopes and the more microbially resistant tricyclic terpane and aromatic steroid hydrocarbon distributions. All the studied oils seem to fit into three major genetic groups which are consistent with the geologic, tectonic, and geographic settings and are presumably related to different source-rock facies. Group I oils are typical of the abundant oil shows in the Epirus province, northwest Greece. Minor but consistent biomarker differences necessitated subgrouping of the Epirus oils, implying derivation from slightly different sources. Group II oils are located in the Katakolon area, northwestern Peloponnese. Group III oils, which are clearly distinct from the other groups, are centered in Zakynthos Island. An oil seep at Trifos, west central Greece, and a subsurface oil from Paxi Island, because of uncertain correlations, are classed intermediate between Group I and II oils. An aromatic steroid hydrocarbon measurement, modified after Mackenzie et al. (1981), appears useful in determining the relative maturity of biodegraded and conventional oils and carbonate rock extracts.

Lipid composition of the pelagic crab Pleuroncodes planipes, its feces, and sinking particulate organic matter in the Equatorial North Pacific Ocean

Fecal pellets from the pelagic crab Pleuroncodes planipes were a substantial portion of the particulate organic matter in a sediment trap deployed at the bottom of the mixed layer in the eastern tropical North Pacific Ocean. The lipids of fresh P. planipes feces were compared to lipids of the sediment trap material, of mixed zooplankton which may comprise part of the diet of the crab, and of the crab itself in order to elucidate the source of organic compounds found in the trap. Hydrocarbons, wax esters, triacylglycerols, steroidal alcohols, steroidal ketones, and fatty acids were determined by capillary gas chromatography and gas chromatography/mass spectrometry. Significant input of lipids via sedimentation of crab fecal material is indicated, and modification of dietary lipid within the gut of the crab is inferred. Labile dietary fatty acids are depleted and sterols enriched in the fecal pellets and trap material relative to the zooplankton and crab. Nuclear saturated and unsaturated 3-ketosteroids and unsaturated steroidal hydrocarbons were detected in the crab, its feces, and in the sediment trap particulate material.

Laboratory models for aromatization and isomerization of hydrocarbons in sedimentary basins

With increasing depth in the Earth's crust, changes take place in the sedimentary distributions of aromatic steroid hydrocarbons and of stereoisomers of certain types of alkanes1,2. The changes occur before and during the early stages of hydrocarbon generation and have been interpreted as resulting from aromatization and configurational isomerization reactions respectively3. We have now brought about an aromatization reaction and an isomerization reaction in the laboratory under free radical conditions, sulphur being chosen as a convenient source of radicals, and have extracted rate constants from the absolute concentration–time functions of the organic substrates. The activation energies and pre-exponential factors were then deduced from the temperature dependence of the rate coefficients. The values of these activation parameters show that, in the laboratory, the aromatization is more temperature dependent than the isomerization reaction, as suggested previously from the distributions of steroidal compounds in sedimentary basins3–5.

Semi‐preparative HPLC of some geologically interesting steroid hydrocarbons

Semi‐preparative HPLC of some geologically interesting steroid hydrocarbons

Molecular changes in sediment lipids as indicators of systematic early diagenesis

Studies of the steroidal hydrocarbons in sediment sequences demonstrate that diagenetic changes in their molecular distributions occur systematically with burial and form a coherent continuum linking the lipid constituents of organisms to those of ancient sediments and petroleums. Such changes are initially caused by (i) microbial processes, then (ii) low-temperature reactions, which appear to be catalysed by clay minerals and, finally, (iii) thermal processes. The molecular composition at stage (iii) can depend on the proportions of the different products generated by the divergent diagenetic pathways of stages (i) and (ii). Organic molecular reactions are sufficiently sensitive that some diagenetic changes are recognizable over small ( ca . 10 m) depth intervals, which should permit a system of molecular diagenetic zones to be devised. This development should enable the low-temperature thermal history of sediments to be assessed accurately. Specific diagenetic reactions within stages (ii) and (iii) also appear to reflect the sediment heat flow; thus, the reaction rates are higher in rapidly subsiding Neogene sedimentary sequences than they are in Cretaceous sediments from passive continental margins.

The aromatization and isomerization of hydro carbons and the thermal and subsidence history of the Nova Scotia margin

The temperature and burial histories of the sediments deposited on the continental margin off Nova Scotia have been modelled. A good match between predicted and observed present-day bottom-hole temperatures is only achieved when the thermal conductivities of sediments are derived from laboratory measurements of representative samples; values commonly quoted in the literature predict too low a geothermal gradient. The temperature history is used to predict the extents of geochemical reactions involving steroid hydrocarbons together with previously derived reaction constants. The reaction extents were measured on 33 samples. In general, agreement between observations and predictions is good. The reactions in some samples, however, appear to have progressed anomalously far for their depths. This is thought to be the result of impregnation of these sediments with oil, which has migrated from depth. The good general agreement between model predictions and observations encourages extrapolation of the model to areas of no sample control, and the reconstruction of the temperature and burial history of the margin. Tentative reconstruction of oil generation from the principal oil source rock of the region may also be attempted. The top of the oil-generation zone currently lies 4 km below the shallow regions of the continental shelf. Model predictions suggest that the Verrill Canyon formation and its equivalents are mature but that younger sediments are not. Maturation of deeper regions of the Verrill Canyon started in the Early Cretaceous, but significant volumes of sediment only entered the oil-generation zone during the Tertiary.

Biological marker characteristics of oils and asphalts from carbonate source rocks in a rapidly subsiding graben, Dead Sea, Israel

A detailed GC/MS study of biological marker compounds in the saturated and aromatic hydrocarbon fractions of oils and asphalts from the Dead Sea area, Israel, provided decisive information to the solution of a long-lasting controversy by showing that the asphalts are products of early generation in an immature stage from the same type of carbonate source rock which generated more mature oils. The asphalts are not biodegraded residues of the oils. Oils from six different wells, and asphalts from wells, outcrops, and a floating block from the Dead Sea all have very similar sterane and triterpane patterns. They all lack rearranged steranes (diasteranes) indicating a carbonate source matrix and compare reasonably well with a sample of Upper Cretaceous bituminous chalk from Nebi Musa. The main difference between the oils and the asphalts is a significantly higher triaromatic to mono- plus triaromatic steroid hydrocarbon ratio in the former. This is explained as a result of rapid subsidence and heating of their source rock close to the deep parts of the Dead Sea graben. The oils thus were generated in the more deeply buried source rock blocks under the graben fill, whereas the asphalts either originate from an immature source rock section closer to the graben rims or represent an earlier phase of generation and expulsion. This study also provides general information on the evolution of biological markers in carbonate source rocks. Low-activation-energy processes, like isomerisation of steranes, appear to occur much faster at low temperatures than in shales. The high sulfur content and less cross-linking of the biogenic organic matter into a complex kerogen structure are suggested to be responsible for this. Care should be taken when using only sterane isomerisation to assess the maturity of hydrocarbons from carbonate rocks and of carbonate-derived oils.

Biological marker distribution and significance in oils and rocks of the Monterey Formation, California

The biological marker distributions of several oils, core extracts and solid bitumens of the Monterey Formation of California have been studied. Sterane, terpane and monoaromatic steroid hydrocarbons were analyzed in samples from the San Joaquin, Los Angeles, Ventura and Santa Maria Basins. The sterane patterns of both oils and extracts are characterized by 1. (a) low relative concentrations of diasteranes, 2. (b) low 20S/20R-5α,14α,17α-ethylcholestane ratios, 3. (c) relatively high concentrations of cholestane ( vs. methyl- and ethylcholestane) isomers. San Joaquin Basin samples contain significant amounts of the 5β isomer, which is generally absent in samples from other basins. The carbon number distribution of 5α,14α,17α,20R steranes is similar for all oils, regardless of API gravity, depth or basin location, and is suggestive of open marine depositional conditions for the source material involved. 17α(H),l8α(H),21β(H)-28,30-Bisnorhopane is present in almost all samples. Certain San Joaquin Basin oils and extracts contain 1. (a) a series of 25-nor hopanes, including 25,28,30-trisnorhopane, 2. (b) a distinctive monoaromatic steroid hydrocarbon distribution, 3. (c) an aliphatic hydrocarbon fraction devoid of n-paraffins. Biological marker characteristics suggest that the Monterey oils examined originated early in the maturational sequence, from elastics-poor source material. API gravities of the Monterey Formation oils examined vary monotonically with 1. (a) bisnorhopane/hopane ratios, 2. (b) aromatized/regular sterane ratios and 3. (c) the concentration of monoaromatized steranes relative to terpanes and regular steranes. These oil gravity correlations exist regardless of sample depth or basin location.

Isomerization and Aromatization of Hydrocarbons and the Paleothermometry and Burial History of Alberta Foreland Basin

The hydrocarbon fractions extracted from 34 Cretaceous shales from a cross section of the Alberta basin have been analyzed using gas chromatography-mass spectrometry. Particular attention has been paid to the extents to which three temperature-dependent geochemical reactions have occurred: isomerization of steranes at C-20; isomerization of hopanes at C-22; and aromatization of C-ring monoaromatic steroid hydrocarbons. Estimates of the kinetic constants of these reactions have been published previously; therefore, constraints may be put on the maximum temperature experienced by the sediments and the time for which this temperature existed. The subsidence history of the Alberta basin is simulated using a lithospheric flexural model in which the lithosphere is downwarped by the loading of overthrusts in the adjacent Cordilleran orogene. When overthrusting ceases, erosion of the overthrusted region lightens the load and the lithosphere rebounds, causing uplift and erosion of the foreland basin. Major overthrusting and therefore deep burial occurred during the Laramide orogeny of Late Cretaceous to mid-Tertiary time. The extent of chemical reactions suggests that the present maturity of the Cretaceous shales is almost entirely a reflection of burial and heating during the Laramide orogeny in a manner that is consistent with the lithospheric flexural model for the basin. The chemical reactions suggest that the paleogeothermal gradient increased systematically away from the foothills of the Rocky Mountains along the profile studied. That a similar trend exists today suggests this situation has persisted at least since the early stages of the Laramide orogeny. This variation is best explained by advective heat transfer. Water entering the basin in the faulted and topographically higher foothills is heated at depth, thereby depressing the geothermal gradient. This hot water then migrates updip and away from the foothills to enhance the geothermal gradients in the Edmonton area and beyond. The route of the migrating hot water is similar to that taken by hydrocarbons from Devonian and Cretaceous source rocks in the deep basin, updip to the oil and tar-sand accumulations of Alberta.

HPLC fractionation and GC-MS determination of aromatic hydrocarbons from oils and sediments

Normal-phase HPLC using a cyano/amino bonded silica stationary phase can provide reliable and rapid fractionation of total neutral fractions from oils and sediments. Separation of aliphatic from aromatic hydrocarbons is possible, but in addition HPLC is able to fractionate aromatic hydrocarbons according to their number of double bonds. Applications of the HPLC fractionation in organic geochemistry are described and illustrated by GC-FID and GC-MS data from an oil and a recent sediment exhibiting a high degree of petrogenic contamination. Alkylphenanthrenes can be obtained free of alkyldibenzothiophenes, allowing evaluation of the methylphenanthrene index by GC-FID without the need for quantification of co-eluting sulphur compounds by GC-FPD. The choice of capillary GC stationary is also considered, particularly with regard to resolution of aromatic steroidal hydrocarbons and alkylphenanthrenes.