Coaly Shale Research Articles

The effect of volcanism to the source rock maturity in Gunung Endut area: Insight for subvolcanic hydrocarbon exploration

Banten region is known to have subvolcanic hydrocarbon system but no proven play despite oil seeps and the potential source rock have been identified in this area. A Geochemical analysis of source rock have been done on Gunung Endut, Banten Province. There are four coaly shale sample from Genteng Formation and Bojongmanik Formation collected and analysed in this study. The purpose of this study is to understand the influence of volcanic environment towards the quality, quantity and maturity of source rock based on TOC, pyrolysis, and vitrinite reflectance analyses. The result obtained showed TOC value between 8–18 wt% which indicated excellent petroleum potential from the source rock. In addition, Pyrolysis data showed S1 value between 0.05–0.19, S2 value between 1.52–11.53, S3 value between 4.10–7.57 and Tmax 414.8–523.2 °C. From both analyses, TOC and Pyrolysis, the source rock is categorized as Type 3 Kerogen producing gas and Type 4. Based on its maturity, three sample are categorized as immature while one specimen is categorized as postmature. Furthermore, Vitrinite Reflectance analysis result shows Ro value between 0.27–0.63 that support the result of pyrolysis analysis. Maturity anomaly found in the sample is presumed to be caused by intrusion that have been identified by the geological mapping in the same region. The condition on the surface may also reflect the source rock in the subsurface. A number of source rock in Banten region may be matured due to intrusion that related to volcanic activities. Subsurface zone with abundance igneous bodies will have different maturity compare to other area. Hence, it is important for petroleum exploration activities in Banten region or other volcanic area to properly identify the distribution of subsurface igneous body due to its effect to the source rock maturity.

Occurrence of carbon nanotubes and implication for the siting of elements in selected anthracites

Petrographic, geochemical, and electron microbeam investigations of selected anthracites and anthracite-rank coaly shales were conducted. The Pennsylvania, Rhode Island, and KwaZu-Natal anthracites show an enrichment in the middle to heavy rare earths (REE) while the Virginia semi-anthracite exhibited a decreasing trend through the light REE, a peak in Gd, and a depletion in the heavy REE. Substitution of As, Hg, and Se in pyrite was most apparent in the Virginia coal. The Pennsylvania, Rhode Island, and KwaZu-Natal anthracites contained spherical carbon nanotube (CNT) structures. The CNTs contained several elements, including Hg, Cd, F, Cl, and Br. While CNTs are known to be produced from coals of varying ranks, this seems to be the first report of naturally occurring CNTs.

Composition of lipids from coal deposits of the Far East: Relations to vegetation and climate change during the Cenozoic

Twenty-one samples of sub-bituminous coal and 1 sample of coaly shale have been collected from different coal seams, representing the Cenozoic coal basins widely distributed in the region of Primorye and Sakhalin (Russia), and NE China (Hunchun deposit). The seams belong to lower Miocene-upper Oligocene (Sineutesovsky), Oligocene-upper Eocene (Pavlovsky), upper Eocene (Ust-Davydovsky), lower Eocene (Uglovsky), and upper Paleocene (Kivdinsky) local chronostratigraphic units.Terpenoid biomarker compositions indicate the contribution of conifers and angiosperms to peat formation. The results are in agreement with paleobotanical data from sedimentary successions closely associated with the seams, highlighting abundant conifers of the taxodioid Cupressaceae and Pinaceae families, as well as Betula, Alnus, Fagus, and Ulmus during Cenozoic in the Far East. In contrast to previous findings about changes in peat-forming vegetation in central Europe, the terpenoid biomarker ratios revealed increased contributions of angiosperms during the Oligocene and gymnosperm domination during Eocene and Miocene. The different evolution may be related to differences in temperature and precipitation distribution, as well as in geomorphology and landscape evolution.A positive relationship between the di-/(di- + tri-)-terpenoid biomarker ratios and δ13C of Oligocene samples indicates the role of varying gymnosperm/angiosperm influences on the δ13C of coal. Differences in vegetation and climate are most probably responsible for the different trends in δ13C of terpenoid biomarkers over the Cenozoic, beside their general variation coupled to the evolution in δ13C of atmospheric CO2.Lower δ2H values of plant-derived lipids during the Oligocene were most probably caused by lower temperatures during coal formation. This conclusion is supported by the results of recent paleobotanical studies, yielding lower mean annual temperatures (MAT) during the Oligocene but comparable values for mean annual precipitation (MAP) during the Eocene and Oligocene in the Primorye region. Pimarane-type diterpenoids are significantly depleted in 2H. The results are in agreement with previous studies identifying different sources of hydrogen and/or different biosynthetic pathways during their formation.

Organic Matter Type, Maturity, Depositional Environmental Characteristics, and Liquid Hydrocarbon Potential of Late Carboniferous Kozlu Bituminous Coal and Coaly Shale Beds (Zonguldak-Amasra Basin, NW Anatolia, Turkey): An Application of Biomarker Geochemistry

The Upper Carboniferous (Westphalian A) Kozlu Formation consisting chiefly of sandstone, thick coal layers, shale, and conglomerate levels crops out in the Zonguldak-Amasra Basin, NW Anatolia. The Kozlu Formation contains a total of 20 mineable coal layers with the thickness varying from 0.5 to 6 m. The lower level of formation is represented by lacustrine deposits, whereas the upper part is made up of thick flood plain sediments and meandering river deposits bearing laterally continuous coal levels. In this study, coal samples taken from coal layers within the Kozlu Formation at the Kozlu Underground Coal Mining site were evaluated using the data obtained from pyrolysis/total organic matter (TOC), gas chromatography, and gas chromatography–mass spectrometry. The average total organic matter (TOC) value of Kozlu coals is 40.28%. The coals are characterized by relatively high hydrogen index (HI) value (average 262 mg HC/gTOC) and very low oxygen index value (2 mg CO2/gTOC). Pyrolysis data indicate that coals contain dominantly type II and less amount of type III kerogen, and Tmax values range from 454 to 468 °C. In gas chromatographs, the recorded distribution consists predominantly of low-carbon-numbered n-alkanes and subordinately of high-carbon-numbered n-alkanes and the terrigenous/aquatic ratio value is very low (0.05–0.09). Pristane abundance is greater than that of phytane, and Pr/Ph ratios are in the range of 1.11–1.60. The sterane abundances in the Kozlu coals are in the following order: C29 > C28 > C27. Coals have high C19 and C20 tricyclic terpane concentrations and high (C19 + C20)/C30 ratio, high C30* (diahopane) and C29Ts concentrations, and high C30*/C29Ts ratio and low C31R/C30 and C29/C30 hopane ratios. The dibenzothiophene-to-phenanthrene ratio of Kozlu coals is found to be very low (0.04–0.14). Based on the pyrolysis and biomarker data, the Kozlu coals are interpreted as being deposited in a suboxic–oxic continental environment in which there is effective input of clay and dominantly terrestrial (with significant lipid-rich components) and bacterial organic matter. High Tmax values, CPI values close to 1, low moretane/hopane (0.23–0.12), equilibrated 22S/(22S + 22R) homopane (for C32), 20S/(20S + 20R) C29 sterane (0.52–0.54) and TA(I)/TA(I + II) steroid ratios, high ββ/(ββ + αα) sterane (0.51–0.55), C30*/C29Ts, C30*/(C30* + C30H), MPI-3(α/β) (1.24–1.41), and MDR and MA(I)/MA(I + II) steroid are indicative of mature–late mature organic matter. Ro values between 0.9 and 1.25% determined from Tmax (454–468 °C) values indicate “high-volatile bituminous B–medium-volatile bituminous” rank for Kozlu coals. Kozlu coals having HI values (up to 331 mg HC/gTOC) extremely higher than those of classical coals indicates that these coals have significant oil and gas generation potential, and high S1 (average 6.04 mg HC/g rock) and S2 (110.08 mg HC/g rock) values imply that they generate notably high amount of liquid hydrocarbons and still have generation potential.

Organic petrography, Rock\u2013Eval pyrolysis and biomarker geochemistry of Maastrichtian Gombe Formation, Gongola Basin, Nigeria

The Maastrichtian Gombe Formation is located within one of the inland basins of Nigeria (Gongola Basin). Surface and borehole samples of coal and interbedded shale of this formation were evaluated to determine the organic matter richness, quality, maturity, source and depositional environment through organic geochemical techniques such as total organic carbon (TOC) determination, Rock–Eval pyrolysis, chromatography and organic petrography. The genetic potential and average TOC value of the coals, shales and coaly shales are 38.03 wt%, 3.14 wt% and 12.1 wt%, respectively, indicating moderate-to-good source potential. HIs are less than 200 mgHC/gTOC for all the samples indicating Type III kerogen for most of the samples (gas prone) and plant contributions from terrestrial sources. The source rocks were characterized by high molecular weight n-alkanes which range from C10–C41 in the coals and C9–C41 in the shales. The n-alkanes distributions in the coals maximize at C29 indicating terrestrial sourced organic matter, while the shales maximize at C16 and C29 indicating mixed sources. Pr/Ph of the coals and shales ranges from (2.15–3.51) to (0.95–2.37), respectively, suggesting fluvio-deltaic deltaic and coastal swamp depositional environments. The predominance of pristane over phytane suggests humic origin of the organic matter. The sterane/hopane values (< 0.6) indicate incorporation of bacterial inputs commonly associated with terrigenous organic matter in the coals. The CPI is greater than unity, Tmax is generally < 435 °C and vitrinite reflectance less than 0.55 Ro for most of the samples and suggest the samples are of low maturity status to expel liquid hydrocarbon.

Biomarker signatures of Upper Cretaceous Latrobe Group petroleum source rocks, Gippsland Basin, Australia: Distribution and geological significance of aromatic hydrocarbons

Aromatic hydrocarbons extracted from Upper Cretaceous (Maastrichtian and Campanian) Latrobe Group coaly shales and shales from the Gippsland Basin were investigated by gas chromatography–mass spectrometry. A variety of 2-ring to 6-ring aromatic hydrocarbons were identified, including both higher-plant-derived and combustion-derived polycyclic aromatic hydrocarbons (PAHs). These aromatic compounds indicate that the Upper Cretaceous coaly shales and shales were deposited in a fluvial/deltaic environment with significant higher plant input and are at a relatively low thermal maturity stage. Higher plant parameters and angiosperm/gymnosperm indices based on aromatic components suggest that higher land plants, including both angiosperms and gymnosperms, were an important part of the palaeovegetation in the Upper Cretaceous. The aromatic angiosperm/gymnosperm index that includes chrysene- and picene-type PAHs is not as reliable for evaluation of relative angiosperm and gymnosperm contributions as the aliphatic indices due to input of combustion-derived PAHs and the complexity of burning conditions altering the relative contributions. However, combustion-derived PAHs and aromatic angiosperm/gymnosperm indices supplement the information from aliphatic hydrocarbons and provide further evidence to support the hypothesis that palaeoclimate cooled from the Campanian to the Maastrichtian.

Origin of organic matter and hydrocarbon potential of Permian Gondwana coaly shales intercalated in coals/sands of the Barapukuria basin, Bangladesh

This paper presents the characteristics of source organic matter (OM), hydrocarbon potential (HC) and the depositional system of Gondwana coaly shales in the Carboniferous-Permian succession in drill hole GDH-40, Barapukuria basin, Bangladesh. Twelve layers intercalated in coals and sands were examined using Hydrogen Index (HI) of Rock Eval analysis, biomarkers in saturated HC fractions, polycyclic aromatic hydrocarbons (PAHs), and stable carbon (δ13Corg) and nitrogen (δ15Ntot) isotope ratios. The coaly shales showed a wide range of total organic carbon (TOC) content (2.3–30.3 wt%), intermediate to high TOC/TN ratios (14–39) and low total sulfur (TS) contents (<0.3 wt%), suggesting deposition in a freshwater environment occasionally influenced by brackish water. OMs with low to moderate HI (20–204 mg HC/g TOC) were deposited in a shallow terrestrial basin. The HC potentials are high in the middle and lower parts of the succession, with increasing TOC content dominated by terrestrial plants. The higher total HC generation potential up to 60.1 mg HC/g is attributed to coaction of high TOC and HI values. The HI values show good positive correlations with Pr/Ph ratios (r = 0.90), n-C>25/n-Ctotal alkanes (r = 0.86), phenanthrene (r = 0.75), methylphenanthrene (MP, r = 0.75), Tm/Ts (r = 0.74), sterane C29/C(27+28+29) (r = 0.69), Pr/n-C17 ratio (r = 0.69) and TS (r = 0.68). The coaly shales also contain abundant retene. Higher δ15N ratios coupled with high HI values suggest that the climate had a dry season. Very small amounts of oleanane and low ratios of oleanane/C30-hopane show negative correlations with HI values (r = −0.68). A significant input of algae and/or planktonic organisms occurred in the upper part of the core, estimated based on regular sterane compositions, but this did not increase the HI values. Relatively abundant hopanes (steranes/hopanes = 0.11–0.40) implied greater contribution of methanogen in the upper part of the succession and increased activity of aerobic bacteria in the middle to lower parts, respectively. Organic maturity is considered to be in the early to medium stage of oil generation, according to C29 sterane 20S/(20S + 20R) ratios of 0.28–0.49. Based on these results, most OMs originated from ferns, pteridospermic gymnosperms, peat mosses and/or submerged/floating plants, occasionally supplemented by a specific gymnosperm OM with epicuticular wax. Potential of HC generation of these coaly shales probably increased with increasing deposition of liptinite materials. Fluoranthene (Fla), pyrene (Py), benzo[e]pyrene (BePy) and benzo[bjk]fluoranthene (Bflas) are abundant PAHs in the coaly shales, and the ratios of low Fla./Py, benzo[a]anthracene (BaAn)/228 and indeno[1,2,3-cd]pyrene/(indeno[1,2,3-cd]pyrene + benzo[ghi]perylene) (InPy/(InPy + BghiP)) suggest that these 4- to 6-ring PAHs were mainly formed by small- to medium-scale wildfires during the dry season.

Characteristic of coaly shale aggregate and its application for the road construction

The waste obtained directly from exploitation of coal and/or from storage is the subject of the paper. The purpose is to describe the properties such material called in this paper the coaly shale aggregate and their applicability as the sterling material for the road construction. Usefulness of such material is normalized by the National Technical Assessment standards.

Depositional Environments and Geochemical Assessments of the Bende Ameki Formation Potential as Petroleum Source Rocks in the Ogbunike Quarry, South-Eastern Nigeria

This paper focuses on investigating the paleoenvironments and hydrocarbon generation potentials of the outcropping Eocene Bende-Ameki Formation at Ogbunike quarry, Anambra Basin southeastern Nigeria, which is the Niger Delta Agbada Formation subsurface equivalent. The fine to coarse sandstones interbedded with parallel laminated grey, coaly shales, and bioturbated claystones were the dominant rock facies. The shales contain Ammobaculities, Ammontium, lenticulina, and Reophax benthic foraminifera of brackish to outer shelf environments. The rock sequence and biofacies associations indicate a fluvial, shoreface to delta environments. The marine and continental paleoenvironments are supported by the concentration and association of redox-sensitive trace elements such as vanadium and nickel of oxic to dysoxic paleoconditions. The twenty shales have a range of TOC from 0.39 - 8.81 wt% (mean 2.2 2 wt%), suggesting a good to very good source rocks. The organic richness is highest within the depth of 2 – 6 m across the quarry. Their genetic potential (S1+S2) ranges from 0.22 - 27.35 (mean 2.8 kgHC/ton) of rock, and hydrogen index from 26 to 292 mgHC/gTOC with a mean of 67.3 mgHC/gTOC. This, however, indicates dominance of Type III gas prone kerogen of terrestrial origin. The oxygenated water column characterized by the presence of benthonic scavengers may not preserve lipidenriched organic constituents of anoxic paleoenvironments which could account for the rare Type II oil and gas prone kerogen in the source rock. The thermal history inferred from the Tmax between 401°C - 424°C suggests that the source rocks are immature at the present stratigraphic level.

Simulating the timing of petroleum generation and expulsion from deltaic source rocks: Implications for Late Cretaceous petroleum system in the offshore Jiza-Qamar Basin, Eastern Yemen

The Mukalla Formation is one of the important petroleum source rocks in the Jiza-Qamar Basin, Eastern Yemen. In this study, coal, coaly shale and shale samples from three wells (Al-Fatak-1, 16/G-1 and 16/E-1) in the offshore Jiza-Qamar Basin were studied. The organic matter richness, kerogen type, thermal maturity, and petroleum generation potential of the Mukalla organic-rich samples were investigated.The analysed Mukalla source rock samples are potentially rich in organic matter of 1.01–84.40% TOC, ranging from good to excellent source rocks. The Mukalla source rocks primarily contain Types II, II–III and III kerogen, anticipating generating mainly oil and gas. This is generally consistent with the pyrolysis–gas chromatography results and further indicates that the Mukalla source rocks can produce high wax oil and condensate/gas. The thermal maturity parameters reveal the Mukalla source rocks are in mature to late-mature and are capable of generating oil and wet gas at the present time. In addition, this study was integrated the geochemical, geo-thermal and geological data in term of basin modeling study to simulate the timing of hydrocarbon generation and expulsion from the Mukalla deltaic source rocks.The basin model results indicate that the oil generation commenced during the late Eocene to late Oligocene, with a conversion ratio of 10–50 TR%. Furthermore, based on TRs of more than 50%, the most of oil was expelled along the micro-fracturing of the Mukalla source rocks and then trapped in the Mukalla Formation itself during the latest Oligocene and continued to present-day.

Geochemical Characterization of the Tazareh Coals, Iran

ABSTRACT This study investigates the abundance, modes of occurrence and origin of major and trace elements in the Jurassic Tazareh coal in the northern Iran. A total of 27 samples (coal, coaly shale and siltstones) were collected and analyzed for trace elements by neutron activation analysis (INAA) and for major elements by X-ray fluorescence. The abundance of these elements is discussed in relation to local geological conditions. The correlation between the various elements is demonstrated through scatter diagrams and the possible genetic associations are discussed. Most elements (Al, Si, Na, K, Fe, Mg, Ti, Ba, Cr and REE) are positively correlated with ash yields that are inorganically associated. Bromine displays statistically signiûcant negative correlations with ash yield. The Ca, Zn, Se, As and Co present mixed modes of occurrence in the coal and probably associate with organic fraction.

2-2-1 炭質頁岩のガス吸着特性 : 夾炭層CO_2貯留に関する研究(2-2 CBM,Session2 天然ガス・メタンハイドレート等,研究発表)

2-2-1 炭質頁岩のガス吸着特性 : 夾炭層CO_2貯留に関する研究(2-2 CBM,Session2 天然ガス・メタンハイドレート等,研究発表)

Organic geochemical characteristics of oils from the offshore Jiza-Qamar Basin, Eastern Yemen: New insight on coal/coaly shale source rocks

Coals, coaly shales and oil show samples from Late Cretaceous sections in the offshore Jiza-Qamar Basin (Yemen) were analysed using organic geochemical analyses to investigate the source of organic matter input and the genetic link between oils and potential source rocks in the basin. The coals and coaly shales have high TOC contents between 6.90 and 77.62wt% and Hydrogen Index (HI) values are largely above 300mg HC/g TOC, indicating that the Late Cretaceous coaly shales and coals as expected are organically rich, and predominantly contain Type III-II kerogens.The oil shows are classified as paraffinic–naphthenic–aromatic (P–N–A) oil with high wax contents, suggesting that the oils were generated from coal and coaly source rocks that were deposited in a deltaic–coastal environment. This is supported by bulk geochemical characteristics and biomarker compositions. A variety of biomarkers n-alkanes, regular isoprenoids, terpanes and steranes indicate that the oil shows were derived predominantly from source rock containing higher plant derived organic matter and were deposited in fluvial to deltaic environments under relatively oxic conditions. The biomarker characteristics and stable isotope compositions of the oils are similar to those of the Late Cretaceous coal and coaly shale rocks. The new data presented in this paper suggests genetic link between oil shows and coal/coaly shale rocks in the offshore Jiza-Qamar Basin and provides new evidence for the oil generative potential of the Cretaceous coals and coaly shales in the basin.

Petrography, biomarker composition, mineralogy, inorganic geochemistry and paleodepositional environment of coals from La Ballesta mine, Peñarroya Basin, Spain

The purpose of this work is to study coal samples from various exposed seams of the La Ballesta mine, at the southeastern edge of the Penarroya-Belmez-Espiel coalfield, southwestern Spain. Shaly seat- and caprocks were also investigated. Petrographic, palynological, and biomarker analyses were carried out. The major elements were determined by X-ray fluorescence (XRF). The trace elements were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). The Pennsylvanian (Westphalian)-age, high volatile bituminous coal studied is a humic coal with vitrinite concentrations of over 86% on a minerals-free basis and low amounts of liptinite and inertinite. The coals have a relatively higher volatile matter yields than the bituminous coals in western areas of the basin with similar vitrinite reflectance values and present both a dark and a light variety of vitrinite. The dark variety is more abundant in the low ash coals considered to have been formed in nearby lacustrine settings. The mineral assemblage of the coals and non-coal (roof and floor) rocks from the La Ballesta mine is dominated by quartz, kaolinite and illite, with minor to trace proportions of epigenetic carbonates, anatase, and K-feldspar, among others. Concentrations of B and B/Be ratios, along with other data, suggest that the La Ballesta coals may have originated from topogenous mires that developed next to lacustrine settings. Coal seams 9, 9bis, and 14 were probably more restricted systems than coaly shale 15, the latter corresponding to swamps associated with alluvial and floodplain environments. Abnormally high concentrations of trace elements such as Li, Rb, Cs, Sc, V and Cr might be explained by the input of detrital minerals into the Penarroya Basin from the outcropping Precambrian and Lower Palaeozoic rocks to the northeast. In this regard, elemental ratios such as Al2O3/TiO2 for the samples suggest that the modes of occurrence of the trace elements, and the minerals, in La Ballesta coals and non-coal rocks are to be mainly attributed to detrital input from felsic to intermediate metamorphic rocks.

Palyno-petrographical Facet and Depositional Account of Gondwana Sediments from East Bokaro Coalfield, Jharkhand

Abstract: Palynological and petrological studies have been undertaken on the Gondwana coal and associated lithologies encountered in borehole EBM-2 of East Bokaro coalfield of Damodar Basin, India. The palynological investigation resulted in the recognition of Assemblage –III (Densipollenites, 27.9 m – 214.30 m), Assemblage – II (Striatopodocarpites + Faunipollenites, 225.00 m – 297.60 m) and Assemblage – I (Faunipollenites + Scheuringipollenites, 307.00m – 433.00 m). Lithofacies study was also done for better understanding of the preservation and abundance/paucity of the spores and pollen in different lithologies as the current borehole has significant thickness of mudstones, shales and siltstone. Palynofacies study and Petrographical studies of coal samples encountered in the borehole were used to determine the depositional environment of the coal precursor peat swamp. Palynological data has revealed the presence of younger Raniganj palynoflora between 27.00-214.30 m depth that is lithologically defined as Barren Measures Formation. This spore pollen study has proved that these sediments were deposited during late early Permian to late Permian period. Further the maceral analysis of organic sediments as well as the Thermal Alteration Index (TAI) has revealed that the coaly shale at 336.5 m depth has hydrocarbon generation potential.

Lithofacies and Sedimentation of Organic Matter in Fine Grained Rocks of Nanggulan Formation in Kulon Progo, Yogyakarta

Fine grained rocks especially shale play a significant role in shale hydrocarbon system. Research on Eocene Nanggulan shale becomes an interest lately since this shale is considered as prospective interval for shale gas source. It potentially contains significant organic matter because coaly sediment is found in this formation as well. Nanggulan Formation fine grained rocks was deposited in various depositional environment from estuary – shallow marine. This paper integrates the result of lithofacies and depositional environment analysis with organic geochemical data to understand the sedimentation process of organic matter. Samples were taken from cores. The result of 14 geochemically analysed samples shows Total Organic Carbon (TOC) content between 0.36–1.00 % for fin e grained rocks (shales) and 12.80 % for coaly shales. Nine samples are categorized as fair and 2 samples are categorized as good source rock. The depositional environment of Nanggulan Formation sediment, which was shallow marine at Late Eocene and estuary (salt marsh) at Early Eocene, produced sediment with higher TOC. Whereas the deposition of sediment in estuary (tidal flat) at Middle Eocene produced lower content of TOC. Vulcanic activity at Middle Eocene also caused less organic material preservation because it produced abundant inorganic material.

Origins of Jurassic oil reserves in the Turpan–Hami Basin, northwest China: Evidence of admixture from source and thermal maturity

Middle–Lower Jurassic coaly shales were considered to be the source of Jurassic oil reserves in the Turpan–Hami Basin. In this study, we investigated the molecular and stable isotopic compositions of 35 gas samples and the geochemical parameters for 28 oil samples to reexamine the origin of these hydrocarbons. We show that the Jurassic natural gas reserves are derived mainly from coaly source rocks in the Middle Jurassic Xishanyao and Lower Jurassic Badaowan formations with maturities varying from 0.6% to 0.9%Ro. However, analysis of the low molecular weight hydrocarbons and diamondoid hydrocarbons shows that the maturities of the oils are clearly higher than those of the Jurassic coal measures and the natural gas generated from them. Their molecular and carbon isotopic compositions indicate that most of the Jurassic oil reserves are derived from pre-Jurassic lacustrine mudstones. The Hongtai gas/condensate field is an exception where the Jurassic coal measures are major contributors of light hydrocarbons. In contrast, the biomarker fingerprints of the Jurassic oils reveal a predominantly humic origin, which is most probably resulted from migration contamination. As such, the Jurassic petroleum system of the Turpan–Hami Basin is a mixed oil system derived from pre-Jurassic lacustrine mudstones and the Middle–Lower Jurassic coaly source rocks. This study opens pre-Jurassic structures in the Turpan–Hami Basin as favorable exploration prospects and illustrates the value of multiple correlation techniques to determine the sources of associated light and heavy hydrocarbons.

Radioactivity and hydrocarbon generation potential of sediments, Gongola Basin, Nigeria

Abstract Samples taken from Well Kolmani-1 in the Gongola Basin in the Upper Benue Trough of Nigeria were studied to estimate the radiogenic heat generated and to analyze the possible impact of radiogenic heat on hydrocarbon generation potential of the sediments. Thirty-eight samples taken from the different formations at intervals of 73.2 m including sand, shale, coaly shale, sandy shale, and shaly sand were analyzed for 40K, 238U, and 232Th using the well calibrated NaI (Tl) Gamma Ray detector System. The results showed that the activity concentrations of the radio-nuclides varied significantly within the sediments. The 40K concentrations were the highest. The radiogenic heat produced ranges widely from 228.44 pW/kg to 1 412.82 pW/kg. In Well Kolmani-1, sands and sandy shale are low heat production sediments, while the shale, coaly shale and silty sands are medium heat production sediments, the potential source rock (shale and coaly shale) medium in heat production (750 pW/kg to 1 500 pW/kg), can produce liquid and gaseous hydrocarbons. It is estimated that the radiogenic heat from the sediments contributed about 10.9% to 20.9% to the total surface heat flux in the basin. Therefore, the radiogenic heat generated by the sediments contributed significantly to the total surface heat flux, and should be taken into consideration in the simulation of basin thermal evolution.

An overview on source rocks and the petroleum system of the central Upper Rhine Graben

The petroleum system of the Upper Rhine Graben (URG) comprises multiple reservoir rocks and four major oil families, which are represented by four distinct source rock intervals. Based on geochemical analyses of new oil samples and as a review of chemical parameter of former oil fields, numerous new oil–source rock correlations were obtained. The asymmetric graben resulted in complex migration pathways with several mixed oils as well as migration from source rocks into significantly older stratigraphic units. Oldest oils originated from Liassic black shales with the Posidonia Shale as main source rock (oil family C). Bituminous shales of the Arietenkalk-Fm. (Lias α) show also significant source rock potential representing the second major source rock interval of the Liassic sequence. Within the Tertiary sequence several source rock intervals occur. Early Tertiary coaly shales generated high wax oils that accumulated in several Tertiary as well as Mesozoic reservoirs (oil family B). The Rupelian Fish Shale acted as important source rock, especially in the northern URG (oil family D). Furthermore, early mature oils from the evaporitic-salinar Corbicula- and Lower Hydrobienschichten occur especially in the area of the Heidelberg-Mannheim-Graben (oil family A). An overview on potential source rocks in the URG is presented including the first detailed geochemical source rock characterization of Middle Eocene sediments (equivalents to the Bouxwiller-Fm.). At the base of this formation a partly very prominent sapropelic coal layer or coaly shale occurs. TOC values of 20–32 % (cuttings) and Hydrogen Index (HI) values up to 640–760 mg HC/g TOC indicate an extraordinary high source rock potential, but a highly variable lateral distribution in terms of thickness and source rock facies is also supposed. First bulk kinetic data of the sapropelic Middle Eocene coal and a coaly layer of the ‘Lymnaenmergel’ are presented and indicate oil-prone organic matter characterized by low activation energies. These sediments are considered as most important source rocks of numerous high wax oils (oil family B) in addition to the coaly source rocks from the (Lower) Pechelbronn-Schichten (Late Eocene). Migration pathways are significantly influenced by the early graben evolution. A major erosion period occurred during the latest Cretaceous. The uplift center was located in the northern URG area, resulting in SSE dipping Mesozoic strata in the central URG. During Middle Eocene times a second uplift center in the Eifel area resulted in SW-NE-directed shore lines in the central URG and contemporaneous south-southeastern depocenters during marine transgression from the south. This structural setting resulted in a major NNW-NW-directed and topography-driven migration pattern for expelled Liassic oil in the fractured Mesozoic subcrop below sealing Dogger α clays and basal Tertiary marls.

Experimental Study on Fractional Compositions of Residual Oil from Shale and Coal of China Using Grain-Based MSSV Pyrolysis

For better understanding compositions and evolutions of residual oil of shale and coal, a grain-based microscale sealed vessel (MSSV) pyrolysis method to whole rock was used to investigate the residual oil contents and its fractional compositions from shale, coal, and coaly shale samples, as well as their variations at different temperatures and maturities. Quantities of extracted oil from residuals and yields of C1 to C5 gases were used to define oil, wet gas, and dry gas windows using equivalent Ro (%) calculated through EasyRo (%) method. Oil windows are defined as 0.6–1.3%Ro for shale and 0.5–1.2%Ro for coal; wet gas windows are 0.9–3.0%Ro for shale and 0.8–2.7%Ro for coal, and dry gas window are 1.3–4.0%Ro for shale and 1.2–4.0%Ro for coal, respectively. Coal shows relatively wider oil window than shale but similar gas window to shale. The maximum residual oil can reach 133.44 mg/g TOC, 69.84 mg/g TOC for marine and lacustrine shale, 10.03 mg/g TOC for coal, and 83.79 mg/g TOC for coaly shale, respec...