Marine Oil Shale Research Articles

Trace Elements in Marine Oil Shale from the Changshe Mountain Area, Northern Tibet, China

With the aim of better understanding geochemistry and assessing potentially hazardous trace elements of marine oil shale, 18 samples from the Changshe Mountain area are studied. The contents of Se, Mo, Cd, As, Bi, Cs, F, and Zn are enriched from 1.8 to 34.5 times as compared with the Clarke values, whereas the other elements are slightly higher/lower than the respective worldwide means. The potentially hazardous trace elements in the Changshe Mountain oil shale include As, Cd, Mo, and Se. Arsenic, Mo, and Se are mainly controlled by organic matter, whereas Cd is mainly present in fossil remains.

Pyrolysis of a Naturally Dried Botryococcus braunii Residue

The extant chlorophyte microalga Botryococcus braunii is a potential source of biofuel. In any future biofuel plant, it may be dried and stockpiled after harvesting and then pyrolyzed to generate oil. To investigate the formation of bio-oil from B. braunii, its naturally occurring residue known as coorongite was pyrolyzed non-isothermally and isothermally under about 1 atm of pure nitrogen carrier gas. The apparent pyrolysis activation energy of coorongite (25 kJ/mol) is much lower than those of most kerogens, which are on the order of 130–250 kJ/mol. However, it approaches that reported for a Moroccan marine oil shale, implying similarities in their responses to pyrolysis. Non-isothermal pyrolysis by thermogravimetry coupled with infrared spectroscopy (TG–IR) revealed coorongite to contain a significant amount of alkanes. Molecular analysis of the isothermal pyrolysates by gas chromatography–mass spectrometry (GC–MS) identified a homologous series of normal alkanes and alkenes (C9–C21), normal ketones (C...

SOURCE REGIONS AND THE SEDIMENTARY PALEOENVIRONMENT OF MARINE OIL SHALE FROM THE BILONG CO AREA, NORTHERN TIBET, CHINA: AN SR-ND ISOTOPIC STUDY

The Bilong Co oil shale zone is located in the South Qiangtang depression, northern Tibet, southwestern China. This zone, together with the Shengli River-Changshe Mountain oil shale zone in the North Qiangtang depression, northern Tibetan Plateau, potentially represents the largest marine oil shale resource in China. Altogether 18 samples of oil shale and micritic limestone were collected from the Bilong Co area to determine their Sr and Nd isotopic composition, as well as discuss sediment sources and paleoenvironmental changes. The Sm-Nd model ages for the Bilong Co oil shale samples support its derivation from the Nadi Kangra source whose model ages reflect the origin of volcanic rocks from the older continental crust by its melting. The Nd isotopic composition of the Bilong Co oil shale is similar to that of Late Triassic Nadi Kangri Formation volcanic-volcani- clastic rocks, which implies that this oil shale stems from said rocks. Generally, the vertical variations of eNd(0) values in the Bilong Co oil shale section are relatively homogeneous, suggesting a stable provenance for sediments. The 87 Sr/ 86 Sr ratio of the Bilong Co oil shale is much higher than that of contemporary seawater. Such a high 87 Sr/ 86 Sr ratio reflects the original com- position of the deposited sediment, both chemical and clastic. In the Bilong Co oil shale area, micritic limestone generally has a slightly lower 87 Sr/ 86 Sr ratio than oil shale. The Sr isotopic fluctuation in the Bilong Co oil shale is closely connected with sea level change. Sea level rise and consequent marine incursion may change the aquatic environment of the pre-existing lagoon, lowering the 87 Sr/ 86 Sr ratio of the precipitation fluid.

Geochemistry of platinum group elements in marine oil shale from the Changshe Mountain area (China): Implications for modes of occurrence and origins

Abstract The Shengli River–Changshe Mountain oil shale zone, located in the North Qiangtang depression, northern Tibet plateau, represents a potentially largest marine oil shale resource in China. Eighteen samples, including oil shale and micritic limestone, were collected from the Changshe Mountain oil shale to determine the concentrations, the modes of occurrence, and origins of platinum group elements (PGEs) in marine oil shale. The oil shale samples from the Changshe Mountain area exhibit low total PGE contents ranging from 3.196 to 8.071 ng/g with a weighted mean value of 5.383 ng/g, while the micritic limestone samples from the Changshe Mountain area exhibit a little lower ranging from 0.471 to 5.669 ng/g. PGEs in oil shale samples are characterized by high contents in Pd (3.23 ng/g), Pt (1.60 ng/g), and Os (0.32 ng/g), as compared to Rh (0.083 ng/g), Ru (0.112 ng/g), and Ir (0.043 ng/g). The individual PGEs of oil shale samples from the Changshe Mountain area exhibit various modes of occurrence. Ru and Ir are mainly controlled by clay minerals and partly present as sulfide. Rh is mainly associated with sulfide and possibly present as clay minerals. Pt is associated with clay minerals and sulfide, and Pd is controlled by organic matter and pyrite, while Os is mainly present in organic matter. Three possible sources of PGEs were identified in oil shale seams in the Changshe Mountain area. Ru and Ir are mainly terrigenous inputs. Rh and Pt are derived from mixed sources (seawater and terrigemnous supply), while Pd and Os are mainly derived from seawater. The terrestrial source of the oil shale seams in the Changshe Mountain oil shale was the Suowa Formation limestone and the Nadi Kangri felsic volcanic rocks.

ORIGIN AND MODE OF OCCURRENCE OF TRACE ELEMENTS IN MARINE OIL SHALE FROM THE SHENGLI RIVER AREA, NORTHERN TIBET, CHINA

With the aim of better understanding of geochemistry of marine oil shale, 25 samples from the Shengli River area were studied. The concentrations of Sr, U, Rb, Pb, and Th were 1.22 to 3.66 times higher compared to the average concentrations in the crust (Clarke values), while the concentrations of other elements were slightly higher/lower compared to the respective Clarke values. Trace elements including U, Pb and Th are important from the environmental point of view. The elements in the Shengli River oil shale may be divided into three groups according to their modes of occurrence, i.e. group A, B, and C. Group A exhibits a relatively high affinity with organic matter. Group B has weakly positive or slightly negative correlation coefficients with ash yield, while Group C shows high positive correlation coefficients with ash yield and possibly has an inorganic affinity. Elements related to terrigenous origin in the oil shale seams in the Shengli River oil shale have originated from two sources: the Nadi Kangri Formation felsic volcanic rocks and the Suowa Formation limestone.

ORGANIC GEOCHEMICAL CHARACTERISTICS OF THE BILONG CO OIL SHALE (CHINA): IMPLICATIONS FOR PALEOENVIRONMENT AND PETROLEUM PROSPECTS

The Bilong Co oil shale is located in the southern part of the Qiangtang basin. This oil shale zone, together with the Shengli River-Changshe Mountain oil shale zone in the northern part of the Qiangtang basin, represents a large marine oil shale resource in China. An organic geochemical investigation of the oil shale was performed to reconstruct paleoenvironment during deposition and to assess petroleum prospects. The TOC content (6.75–19.2 wt.%) and S2 values (5.96–70.2 mg HC/g rock) of oil shale samples from the Bilong Co area are relatively high indicating that the oil shale from the Bilong Co area has shale oil producing potential. The thermal maturity assessed from Tmax and other maturity-related parameters (Ts/(Ts+Tm), C32Hop S/(S+R), C29St S/(S+R), and C29St ββ/(αα+ββ)) shows a mature stage of the organic matter. Analyzed oil shale samples from the Bilong Co area are characterized by a dominance of low carbon number molecular compositions with relatively high C 21- /C 21+ (0.82–1.95), low Pr/Ph (0.13–0.80), high concentrations of homohopanes (C31-C35), and a slight predominance of C29 steranes, indicating reducing environments, highly saline conditions, a strong contribution of inferior aquatic organisms, and some influence of terrestrial organic matter. Highly similar biomarker characteristics between the Bilong Co oil shale and nearby Zharen-Longeni crude oil in the southern Qiangtang depression suggest that the oil shale from the Bilong Co area has made a strong contribution to the generation of Zharen-Longeni crude oil.

Concentration and mode of occurrence of trace elements in marine oil shale from the Bilong Co area, northern Tibet, China

Abstract The Bilong Co oil shale zone is located in the South Qiangtang depression. This zone, together with the Shengli River-Changshe Mountain oil shale zone in the North Qiangtang depression, northern Tibet plateau, represents a potentially large marine oil shale resource in China. With the aim of better understanding geochemistry of marine oil shale, 18 samples from the Bilong Co area are studied and 56 elements in them are determined. The contents of Mo, Se, Cd, Cs, As, Bi, U Rb, Pb, Th, Li, Sr, and Zn are enriched from 1.3 to 35.0 times as compared with the average concentration in the crust (Clarke values), whereas the other elements are slightly higher/lower than the respective Clarke values. Compared to common Australian oil shales, the contents of Ce, Co, Cs, F, Ga, Hf, Nb, Nd, Pb, Pr, Rb, Sc, Sn, Th, and Zr in the Bilong Co oil shale samples exhibit relatively high levels, whereas As, Br, Cd, Cr, Cu, Dy, Er, Eu, Ho, Lu, Mo, Ni, Se, Tb, Tm, U, V, Y, Yb, and Zn are relatively depleted. However, the distribution patterns of trace elements are quite similar indicating that trace-element speciation in oil shale is governed by general processes rather than by individual geochemical mechanisms within one particular sample. The elements in the Bilong Co oil shale may be classified into three groups of association according to their modes of occurrence, i.e. Groups A, B, and C. Group A (Si–Al–K–Na–Ti–Zr–Sc–Th–Sn–Nb–Ga–Ta–Be–Hf–Cs–Li–Rb–ash–REEs) is strongly correlated with ash yield and mainly has an inorganic affinity. Group B (Cr–W–Mg–Mn–Br–F–Sr–Ba) has weakly or negatively positive correlation coefficients (with an exception of F) with ash yield. Group C (Zn–Bi–Cd–Ca–Fe–Pb–Hg–Co–Cu–Ni–P–Mo–Se–U–As–V) shows negative correlation coefficients with ash yield (with an exception of Bi) and possibly has an organic affinity.

Geochemistry and origin of rare earth elements (REEs) in the Shengli River oil shale, northern Tibet, China

The Shengli River-Changshe Mountain oil shale zone, located in the North Qiangtang depression, northern Tibet plateau, represents a potentially large marine oil shale resource in China. Twenty-eight samples including oil shale, micritic limestone and marl were collected from the Shengli River area to determine the contents and distribution patterns of rare earth elements (REEs) in marine oil shale. Oil shale samples from the Shengli River area have high ash yield (61.86–67.48%) and TOC content (8.02–13.67%) with low total sulfur (S t,d) content (0.76–1.39%) and intermediate shale oil content (3.60–16.30%). The total rare earth element (ΣREE) content in oil shale samples is notably depleted (46.79–67.90 μg/g), approximately one third of the mean value of the North American Shale Composite (NASC), and lower than that of world-wide black shales and Chinese coals, but higher than that of world-wide coals and micritic limestone samples (29.21 μg/g) from the Shengli River area. The oil shale samples from the Shengli River area exhibit shale-like Chondrite or NASC-normalized REE patterns similar to those of micritic limestone and marl samples from this area, indicating that REEs of these different lithological samples may have been derived from a similar terrigenous source. REE contents of oil shale samples are highly positive correlated with ash yield and show a positive correlation with Fe and a weakly positive correlation with organic sulfur, and the vertical variations of REEs mainly follow those of Si, Al, K and Ti. All these facts indicate that the REE contents in oil shale seams are mainly controlled by clay minerals and, to a lesser extent, by pyrite, as well as partly associated with oil shale organic constituents. Rare earth elements in the Shengli River oil shale have originated from two sources: a felsic volcanic rock source and a clastic or/and limestone source.

Concentrations and modes of occurrence of platinum group elements in the Shengli River oil shale, northern Tibet, China

The Shengli River–Changshe Mountain oil shale zone, located in the North Qiangtang depression, northern Tibet plateau, represents a potentially large marine oil shale resource in China. Twenty-one samples including oil shale, micritic limestone and marl were collected from the Shengli River area to determine the contents, distribution patterns and modes of occurrence of platinum group elements (PGEs) in marine oil shale. Oil shale samples from the Shengli River area have high ash yield (61.86–67.48%) and total organic carbon content (8.02–13.67%) with low total sulfur content (0.76–1.39%) and intermediate shale oil content (3.60–16.30%). The total PGE content in oil shale samples is very low (average 1.749 ng/g), approximately half the mean value of Chinese coals, but higher than that of USA coals. PGEs in oil shale samples from the Shengli River area are characterized by high Pd (average 0.82 ng/g), Os (average 0.15 ng/g) and Pt (average 0.66 ng/g) contents compared with Ru (average 0.05 ng/g), Rh (average 0.05 ng/g) and Ir (average 0.02 ng/g). Distribution patterns of individual PGEs are not uniform in the Shengli River oil shale section. The lower marl layer is characterized by the highest Ru and Rh concentrations, whereas the upper marl layer is characterized by the highest Os and Ir concentrations. The highest Pt and Pd concentrations are found in the lower and upper parts of oil shale seams, respectively. The individual PGEs in the oil shale samples from the Shengli River area exhibit various modes of occurrence. Ru is mainly present in P-bearing minerals and partly associated with the clay and Ca-bearing minerals. Rh is mainly controlled by clay minerals and partly present in the form of apatite. Os occurs mainly in clay minerals and, to a lesser extent, in pyrite and apatite. Pd and Ir are mainly associated with Ca-bearing minerals and apatite. Pt is mainly present in Ca-bearing minerals and partly related to organic matter and apatite.

GEOCHEMISTRY OF RARE EARTH ELEMENTS IN MARINE OIL SHALE – A CASE STUDY FROM THE BILONG CO AREA, NORTHERN TIBET, CHINA

The Bilong Co oil shale zone is located in the South Qiangtang depression. This zone, together with the Shengli River-Changshe Mountain oil shale zone in the North Qiangtang depression, northern Tibet plateau, represents a potentially large marine oil shale resource in China. The content and modes of occurrence of rare earth elements (REEs) in selected oil shale samples from the Bilong Co area were studied by inductively-coupled plasma mass spectrometer (ICP-MS) and statistical methods, respectively. The total organic carbon (TOC) content (6.75–19.20%) of oil shale samples is high with low or moderate total sulfur (St, d) content (1.05–2.00%) and intermediate shale oil content. The total rare earth element (∑REE) content of oil shale samples ranges from 63.69 to 117.85 µg/g. The average REE content of 13 oil shale samples from the Bilong Co area is slightly higher than that of USA coals and micritic limestone samples from the Bilong Co area, but lower than that of worldwide black shales. The oil shale samples from the Bilong Co area show shale-like chondrite or NASC-normalized REE patterns similar to those of micritic limestone samples from this area, indicating that REEs of these different lithological samples may have been derived from a similar terrigenous source. REE content of oil shale samples is highly positively correlated with ash yield and shows a positive correlation with Fe and a negative correlation with organic sulfur, and the vertical variations of REEs mainly follow those of Si, Al, K, Na and Ti. All these facts indicate that the REE content in oil shale seams is mainly controlled by clay minerals and, to a less extent, by pyrite, as well as partly associated with oil shale organic constituents.

REE geochemistry of marine oil shale from the Changshe Mountain area, northern Tibet, China

Abstract The Shengli River–Changshe Mountain oil shale zone, located in the North Qiangtang depression, northern Tibet plateau, represents a potentially large marine oil shale resource in China. The contents and distribution patterns of rare earth elements (REEs) in selected oil shale and micritic limestone samples from the Changshe Mountain area were studied by inductively-coupled plasma mass spectrometer (ICP-MS). Analyzed oil shale samples from the Changshe Mountain area are characterized by high total organic carbon (TOC) contents (7.02–16.32%) and ash yields (53.22–82.12%) with shale oil contents from 3.85% to 11.76%. The total rare earth element (∑ REE) contents in oil shale samples are 68.19 μg/g, close to those of US coals, and higher than those of micritic limestone samples (37.69 μg/g) from the Changshe Mountain area, but lower than those of world-wide black shales, common Chinese coals, and North American Shale Composite. There are two types, A and B, of distribution patterns of REEs in the Changshe Mountain oil shale samples. Type A shows negligible Ce anomalies (0.97–1.01), with slightly higher ∑ REE concentrations (36.87–118.38 μg/g) and LREE/HREE (6.79–10.74) and (La/Yb) n (6.68–8.36) ratios, whereas type B exhibits a slightly negative Ce anomaly (0.84–0.88), with slightly lower ∑ REE concentrations (13.73–15.31 μg/g) and LREE/HREE (5.54–6.34) and (La/Yb) n (5.03–6.65) ratios. Both types A and B oil shales are characterized by distinctly sloping LREE trends (La n /Sm n = 3.60–5.44) accompanied by flat HREE trends, with distinct Eu negative anomalies (0.51–0.69). The vertical variations of ∑ REE contents are similar to those of ash, Si, Al, K, Na, Ti and Fe, and show a negative correlation with organic sulfur and organic carbon, indicating that the REE contents in oil shale seams are mainly controlled by land-derived detritus.

VARIATIONS IN COMPOSITION, PETROLEUM POTENTIAL AND KINETICS OF ORDOVICIAN – MIOCENE TYPE I AND TYPE I‐II SOURCE ROCKS (OIL SHALES): IMPLICATIONS FOR HYDROCARBON GENERATION CHARACTERISTICS

Lacustrine and marine oil shales with Type I and Type I‐II kerogen constitute significant petroleum source rocks around the world. Contrary to common belief, such rocks show considerable compositional variability which influences their hydrocarbon generation characteristics. A global set of 23 Ordovician – Miocene freshwater and brackish water lacustrine and marine oil shales has been studied with regard to their organic composition, petroleum potential and generation kinetics. In addition their petroleum generation characteristics have been modelled. The oil shales can be classified as lacosite, torbanite, tasmanite and kukersite. They are thermally immature. Most of the shales contain >10 wt% TOC and the highest sulphur contents are recorded in the brackish water and marine oil shales. The kerogen is sapropelic and is principally composed of a complex of algal‐derived organic matter in the form of: (i) telalginite (Botryococcus‐, Prasinophyte‐ (Tasmanites?) or Gloeocapsomorpha‐type); (ii) lamalginite (laminated, filamentous or network structure derived from Pediastrum‐ or Tetraedron‐type algae, from dinoflagellate/acritarch cysts or from thin‐walled Prasinophyte‐type algae); (iii) fluorescing amorphous organic matter (AOM) and (iv) liptodetrinite. High atomic H/C ratios reflect the hydrogen‐rich Type I and Type I‐II kerogen, and Hydrogen Index values generally >300 mg HC/g TOC and reaching nearly 800 mg HC/g TOC emphasise the oil‐prone nature of the oil shales. The kerogen type and source rock quality appear not to be related to age, depositional environment or oil shale type. Therefore, a unique, global activation energy (Ea) distribution and frequency factor (A) for these source rocks cannot be expected. The differences in kerogen composition result in considerable variations in Ea‐distributions and A‐factors. Generation modelling using custom kinetics and the known subsidence history of the Malay‐Cho Thu Basin (Gulf of Thailand/South China Sea), combined with established and hypothetical temperature histories, show that the oil shales decompose at different rates during maturation. At a maximum temperature of ∼120°C reached during burial, only limited kerogen conversion has taken place. However, oil shales characterised by broader Ea‐distributions with low Ea‐values (and a single approximated A‐factor) show increased decomposition rates. Where more deeply buried (maximum temperature ∼150°C), some of the brackish water and marine oil shales have realised the major part of their generation potential, whereas the freshwater oil shales and other brackish water oil shales are only ∼30–40% converted. At still higher temperatures between ∼165°C and 180°C all oil shales reach 90% conversion. Most hydrocarbons from these source rocks will be generated within narrow oil windows (∼20–80% kerogen conversion). Although the brackish water and marine oil shales appear to decompose faster than the freshwater oil shales, this suggests that with increasing heatflow the influence of kerogen heterogeneity on modelling of hydrocarbon generation declines. It may thus be critical to understand the organic facies of Type I and Type I‐II source rocks, particularly in basins with moderate heatflows and restricted burial depths. Measurement of custom kinetics is recommended, if possible, to increase the accuracy of any computed hydrocarbon generation models.

Geochemical and palynological investigation of the Shengli River marine oil shale (China): Implications for paleoenvironment and paleoclimate

Abstract The Shengli River oil shale, located in the North Qiangtang depression, northern Tibet plateau, represents a potential large marine oil shale resource in China. A geochemical and palynological investigation of the oil shale was performed to reconstruct paleoenvironment and paleoclimate during deposition. The total organic carbon (TOC) contents (15.05%–20.34%) and S 2 values (103.27–129.12 mg HC/mg rock) of oil shale samples are high, and the organic matter consists mainly of type II kerogen. The thermal maturity assessed from PI (0.033–0.036) and T max (433–436) shows an immature to early mature stage of the organic matter. Analyzed oil shale samples from the Shengli River area are characterized by a dominance of low carbon number molecular compositions with high C 21 − /C 21 + (2.10–2.83), low Pr/Ph (0.63–0.75) and high concentrations of C 27 sterane and homohopanes (C 31 –C 35 ), indicating reducing environments, highly saline conditions, and a prevalent contribution of algae to organic matter accumulation. The analyzed oil shale samples have an uncommonly heavy C isotopic composition, ranging in δ 13 C values of bulk organic matter from − 20.79‰ to − 21.78‰. The enrichment in 13 C is mainly attributed to the high productivity of algae rather than solely the result of hypersalinity. Composition of palynofloras from oil shale samples suggests that the climate of the Qiangtang basin region during the deposition of oil shales was warm and humid or sub-humid.

SEDIMENTOLOGICAL INVESTIGATIONS OF THE SHENGLI RIVER-CHANGSHE MOUNTAIN OIL SHALE (CHINA): RELATIONSHIPS WITH OIL SHALE FORMATION

Recently a new oil shale belt was discovered in the Changshe Mountain area, northern Tibet, China. This belt, combined with the oil shale zone found in the Shengli River area, represents a large marine oil shale resource in China. Three facies associations have been recognized concerning the deposition of oil shale in the Qiangtang basin: fluvial-delta, tidal flat-lagoon and shallow marine facies associations. Oil shales were mainly deposited in lagoonal environments. The deposition of the Shengli River-Changshe Mountain oil shale may be controlled by many factors, such as sea level change, differential palaeotopography and palaeoclimate change. Sea level rise and consequent marine incursion may change the aquatic environment of pre-existing lagoon. Differential palaeotopography may control the lateral distribution of oil shale seam, while palaeoclimate change may be partially responsible for the vertical facies change from oil shale to gypsum-salt deposition.

Re-Os (ICP-MS) DATING OF MARINE OIL SHALE IN THE QIANGTANG BASIN, NORTHERN TIBET, CHINA

Marine oil shale from the Shenglihe oil shale section in the Qiangtang basin, northern Tibet, China, was dated by the Re-Os technique using Carius Tube digestion, Os distillation, Re extraction by acetone and ICP-MS measurement. An isochron was obtained giving an age of 101±24 Ma with an initial 187 Os/ 188 Os ratio of 1.84±0.11(n = 11, MSWD = 3.5). The Re-Os age agrees with the geological age derived from biostratigraphic data, indicating the great potential of the Re-Os method for dating the marine oil shale. Our new data (Bilong Co oil shale) also show that the samples must derive from the same layer of oil shales to determine an accurate and precise depositional age for the marine oil shale with the 187 Re- 187 Os radioisotope system.

Porphyrin Distributions in Lacustrine and Marine Shales as Indicators of Paleodepositional Environments: ABSTRACT

Porphyrins, organic molecules derived from chlorophyll, were assessed as potential paleoenvironmental indicators (biomarkers) of oil shales. The differences between the porphyrins from shales and coals are well established. However, the more subtle differentiation between the porphyrin distribution patterns of the lacustrine and marine oil shales is not documented. The lacustrine shales studied here are from Tertiary fault basins in China. The Mesozoic marine oil shales came from a variety of geographic and stratigraphic settings. The bulk of porphyrins occurs in the carbon number range from C[sub 30] to C[sub 33]. The C[sub 32] porphyrin is the most abundant irrespective of shale origin. The acustrine shales contain porphyrins in the C[sub 28]-C[sub 35] range whereas the marine shales usually have porphyrins in the C[sub 25]-C[sub 36] range. The DPEP, ie., Class A-2 porphyrins are dominant both in lacustrine and marine shales. However, the DPEP ie., Class A-4 porphyrins are absent in lacustrine shales. Moreover, marine shales contain vanadyl porphyrins whereas lacustrine shales contain nickel porphyrins. Finally, the absolute amounts of posphyrins in lake sediments are much lower than in marine sediments. Differences amongst porphyrin characteristics of thermally immature organic-rich shales are only in part attributed to the great variety of theirmore » precursor molecules, i.e., chlorophylls. Most likely, the dominant control was exerted by the intensity of anoxia during early diagenesis.« less

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.

Petrographic classification of oil shales

Oil shales are a diverse group of rocks that contain mineral matter and organic matter. The organic matter is derived from terrestrial, lacustrine and marine organisms. The maceral nomeclature system of the International Committee for Coal Petrology, used widely in coal petrography and petroleum source-rock studies, is suitable for describing the organic matter in oil shales provided the terminology for organic matter derived from algal precursors is divided into two submacerals — telalginite and lamalginite. Macerals of the liptinite group, including alginite, are volumetrically important constituents of oil shales and are the major source of the shale oil that is formed during pyrolysis. Liptinite is easily characterized and quantified using fluorescence mode microscopy and thus the type and abundance of liptinite can be used as a basis for a petrographic classification of oil shales. Oil shales are grouped, using the environmental of deposition as the discriminatory criterion, into the three primary divisions of terrestrial, lacustrine and marine oil shales. Type and abundance of liptinite is then used to subdivide these three groups into cannel coal, torbanite, lamosite (further subdivided into Rundle-type lamosite and Green River-type lamosite), marinite, tasmanite and kuckersite.

The effect of organic matter type and organic carbon content on Rock-Eval hydrogen index in oil shales and source rocks

The amount of “gas-prone” kerogen (woody, fungal and “inert”) and the organic carbon content (TOC) are the two predominant factors affecting the hydrogen index (HI) in the 226 samples of lacustrine and marine oil shales and source rocks studied. HI decreases as a function of the amount of “gas-prone” kerogen and increases as a function of TOC. In addition, the type of amorphous kerogen influences the hydrogen index, and this can be roughly estimated from the fluorescence intensity of the amorphous kerogen. Nearly eighty percent of the variation in HI in these samples can be accounted for by the percentage of “gas-prone” kerogen, the TOC content, and the fluorescence of the amorphous kerogen in a multiple regression analysis. Hydrogen index increases as a function of TOC up to about 10% TOC (the relationship can be approximated by a quadratic equation) and then levels off. A possible explanation for this is that the capability of a rock to generate and expel hydrocarbons during pyrolysis increases with TOC. When the retention capacity of the rock matrix is saturated (at about 10% TOC) further increases in TOC have no effect on HI. It is also possible that the quality (i.e. oil-proneness) of the amorphous kerogen is poorer in low TOC samples than in high TOC samples. The samples came from the following oil shales and source rocks: Rundle (Queensland Eocene-Miocene), Mae Sot (northwestern Thailand, Eocene-Pliocene), River River (northwestern Colorado, Eocene), Toolebuc (western Queensland, Late Albian), the “Posidonienschiefer” (southwestern Germany, Toarcian), an Argentinian lacustrine deposit (Eocene-Miocene), the Kimmeridgian sections from four North Sea wells (blocks 21, 30, and 210), Monterey Shale (California, Miocene), and sections from six wells from the Alaskan Tertiary (North Slope, North Aleutian Shelf, Navarin Basin, Norton Sound). Most samples appear to be thermally immature (T.A.I. less than 1.8; R o less than 0.6%) so they should be considered only potential source rocks. The lacustrine oil shales have a higher conversion ratio (yeild/TOC or S 1 + S 2/TOC) than do the marine oil shales in samples with only amorphous and algal kerogen. These, in turn, have a higher conversion ratio than the marine source rocks. These differences are roughly reflected in the fluorescence intensity of the amorphous kerogen. Free hydrocarbons are higher in the marine source rocks than in the marine oil shales, and are lowest in the lacustrine oil shales.

Permian

Permian