Effects of inherent pyrite on hydrocarbon generation by thermal pyrolysis: An example of low maturity type-II kerogen from Alum shale formation, Sweden

Source-rock samples from the Upper Triassic Yanchang Formation in the Ordos Basin of China were geochemically characterized to determine variations in depositional environments, organic-matter (OM) source, and thermal maturity. Total organic carbon (TOC) content varies from 4 wt% to 10 wt% in the Chang 7, Chang 8, and Chang 9 members — the three OM-rich shale intervals. The Chang 7 has the highest TOC and hydrogen index values, and it is considered the best source rock in the formation. Geochemical evidence indicates that the main sources of OM in the Yanchang Formation are freshwater lacustrine phytoplanktons, aquatic macrophytes, aquatic organisms, and land plants deposited under a weakly reducing to suboxic depositional environment. The elevated [Formula: see text] sterane concentration and depleted [Formula: see text] values of OM in the middle of the Chang 7 may indicate the presence of freshwater cyanobacteria blooms that corresponds to a period of maximum lake expansion. The OM deposited in deeper parts of the lake is dominated by oil-prone type I or type II kerogen or a mixture of both. The OM deposited in shallower settings is characterized by increased terrestrial input with a mixture of types II and III kerogen. These source rocks are in the oil window, with maturity increasing with burial depth. The measured solid-bitumen reflectance and calculated vitrinite reflectance from the temperature at maximum release of hydrocarbons occurs during Rock-Eval pyrolysis ([Formula: see text]) and the methylphenanthrene index (MPI-1) chemical maturity parameters range from 0.8 to [Formula: see text]. Because the thermal labilities of OM are associated with the kerogen type, the required thermal stress for oil generation from types I and II mixed kerogen has a higher and narrower range of temperature for hydrocarbon generation than that of OM dominated by type II kerogen or types II and III mixed kerogen deposited in the prodelta and delta front.

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Exceptional preservation in calcareous nodules

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1985.0139 ◽

1985 ◽

Vol 311 (1148) ◽

pp. 67-73 ◽

Cited By ~ 65

Keyword(s):

Lower Triassic ◽

Environmental Indicators ◽

Carnic Alps ◽

Upper Cambrian ◽

Exceptional Preservation ◽

Alum Shale ◽

Shale Formation ◽

The Common ◽

Santana Formation ◽

Barstow Formation

Preservation of soft integument in calcareous nodules seems to be more widespread geographically and stratigraphically than hitherto realized. It cannot be recognized in the field, and to recover such material requires special etching techniques. Such preservation can be of exceptional quality, with fossils preserved three dimensionally either by secondary phosphatization or by silicification. Coating as well as the replacement of integument has been observed even within the same sample. Methodical search for such preservation may be based on the common denominators of depositional, geochemical, and environmental indicators in previously described occurrences. As such exceptionally preserved material may be rare within the samples, large quantities of rock have to be prepared. The examples described here are from anthraconitic limestones (Orsten) of the Upper Cambrian Alum Shale Formation in Sweden. They are now known from many localities and from different trilobite zones. In addition nodules from the Lower Cretaceous Santana Formation in Brazil, the Upper Devonian cephalopod limestone in the Carnic Alps, the Lower Triassic of Spitzbergen and the Miocene Barstow Formation in California have all yielded extremely fine material.

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Evolution characteristics and model of nanopore structure and adsorption capacity in organic-rich shale during artificial thermal maturation: A pyrolysis study of the Mesoproterozoic Xiamaling marine shale with type II kerogen from Zhangjiakou, Hebei, China

Energy Exploration & Exploitation ◽

10.1177/0144598718810256 ◽

2018 ◽

Vol 37 (1) ◽

pp. 493-518 ◽

Cited By ~ 2

Author(s):

Liangwei Xu ◽

Yang Wang ◽

Luofu Liu ◽

Lei Chen ◽

Ji Chen

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

Surface Area ◽

Pore Volume ◽

Oil Shale ◽

Hydrocarbon Generation ◽

Type Ii ◽

Thermal Maturation ◽

Evolution Characteristics ◽

Nanopore Structure

Thermal maturity has a considerable impact on hydrocarbon generation, mineral conversion, nanopore structure, and adsorption capacity evolution of shale, but that impact on organic-rich marine shales containing type II kerogen has been rarely subjected to explicit and quantitative characterization. This study aims to obtain information regarding the effects of thermal maturation on organic matter, mineral content, pore structure, and adsorption capacity evolution of marine shale. Mesoproterozoic Xiamaling immaturity marine oil shale with type II kerogen in Zhangjiakou of Hebei, China, was chosen for anhydrous pyrolysis to simulate the maturation process. With increasing simulation temperature, hydrocarbon generation and mineral transformation promote the formation, development, and evolution of pores in the shale. The original and simulated samples consist of closed microspores and one-end closed pores of the slit throat, all-opened wedge-shaped capillaries, and fractured or lamellar pores, which are related to the plate particles of clay. The increase in maturity can promote the formation and development of pores in the shale. Heating can also promote the accumulation, formation, and development of pores, leading to a large pore volume and surface area. The temperature increase can promote the development of pore volume and surface area of 1–10 and 40-nm diameter pores. The formation and development of pore volume and surface area of 1–10 nm diameter pores are more substantial than that of 40-nm diameter pores. The pore structure evolution of the sample can be divided into pore adjustment (T < 350°C, EqRo < 0.86%), development (350°C < T < 650°C, 0.86% < EqRo < 3.28%), and conversion or destruction stages (T > 650°C, EqRo > 3.28%). Along with the increase in maturity, the methane adsorption content decreases in the initial simulation stage, increases in the middle simulation stage, and reaches the maximum value at 650°C, after which it gradually decreases. A general evolution model is proposed by combining the nanopore structure and the adsorption capacity evolution characteristics of the oil shale.

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Geochemical characterization of hydrocarbon source rocks of the Triassic-Jurassic time interval in the Mandawa basin, southern Tanzania: Implications for petroleum generation potential

South African Journal of Geology ◽

10.25131/sajg.123.0037 ◽

2020 ◽

Vol 123 (4) ◽

pp. 587-596

Author(s):

A. Emanuel ◽

C.H. Kasanzu ◽

M. Kagya

Keyword(s):

Source Rocks ◽

Geochemical Data ◽

Time Interval ◽

Type I ◽

Hydrocarbon Generation ◽

Type Ii ◽

Geochemical Characterization ◽

Type Iii ◽

Petroleum Generation

Abstract Triassic to mid-Jurassic core samples of the Mandawa basin, southern Tanzania (western coast of the Indian Ocean), were geochemically analyzed in order to constrain source rock potentials and petroleum generation prospects of different stratigraphic formations within the coastal basin complex. The samples were collected from the Mihambia, Mbuo and Nondwa Formations in the basin. Geochemical characterization of source rocks intersected in exploration wells drilled between 503 to 4042 m below surface yielded highly variable organic matter contents (TOC) rated between fair and very good potential source rocks (0.5 to 8.7 wt%; mean ca. 2.3 wt%). Based on bulk geochemical data obtained in this study, the Mandawa source rocks are mainly Type I, Type II, Type III, mixed Types II/III and Type IV kerogens, with a predominance of Type II, Type III and mixed Type II/III. Based on pyrolysis data (Tmax 417 to 473oC; PI = 0.02 to 0.47; highly variable HI = 13 to 1 000 mg/gTOC; OI = 16 to 225 mg/g; and VR values of between 0.24 to 0.95% Ro) we suggest that the Triassic Mbuo Formation and possibly the mid-Jurassic Mihambia Formation have a higher potential for hydrocarbon generation than the Nondwa Formation as they are relatively thermally mature.

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Skeletal carbonate productivity and phosphogenesis at the lower–middle Cambrian transition of Scania, southern Sweden

Geological Magazine ◽

10.1017/s0016756809990021 ◽

2009 ◽

Vol 147 (1) ◽

pp. 59-76 ◽

Cited By ~ 14

Author(s):

J. JAVIER ÁLVARO ◽

PER AHLBERG ◽

NIKLAS AXHEIMER

Keyword(s):

Primary Productivity ◽

Microbial Mats ◽

High Energy ◽

Nutrient Supply ◽

Energy Conditions ◽

Southern Sweden ◽

Middle Cambrian ◽

Alum Shale ◽

Shale Formation ◽

Reducing Environment

AbstractThe lower–middle Cambrian transitional interval of Scania is largely represented by condensed limestone beds, lithostratigraphically grouped in the Gislöv Formation (1–5.7 m thick), and the Forsemölla and Exsulans Limestone beds (lower part of the Alum Shale Formation, up to 4 m thick). The strata display a combination of skeletal carbonate productivity, episodic nucleation of phosphate hardground nodules, and polyphase reworking recorded on a platform bordering the NW corner of Baltica. The shell accumulations can be subdivided into three deepening-upward parasequences, separated by distinct erosive unconformities. The parasequences correspond biostratigraphically to the Holmia kjerulfi, Ornamentaspis? linnarssoni and Ptychagnostus gibbus zones, the latter two generally being separated by a stratigraphic gap that includes the middle Cambrian Acadoparadoxides oelandicus Superzone. Except for the Exsulans Limestone, the carbonates reflect development of a prolific epibenthic biota, dominated by filter-feeding nonreefal chancelloriid–echinoderm–sponge meadows, rich in trilobites and brachiopods, and which were subjected to high-energy conditions. The absence of microbial mats or veneers encrusting the erosive surfaces of these event-concentration low-relief shoal complexes may be related to long hiatal episodes resulting in microboring proliferation. High levels of nutrient supply resulted in high primary productivity, eutrophic conditions, glauconite precipitation, phosphogenesis (in some case microbially mediated) and microendolithic infestation. An early-diagenetic mildly reducing environment is suggested by the presence of authigenic (subsequently reworked) pyrite, which contrasts with the syndepositional normal oxygenated conditions reflected by macroburrowing and the abundance of benthic fossils.

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Anopolenus henrici Salter, a middle Cambrian (Drumian) centropleurid trilobite from the Alum Shale Formation of Scandinavia

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-2018-66-13 ◽

2018 ◽

Vol 66 ◽

pp. 223-228

Author(s):

Thomas Weidner ◽

Jan Ove R. Ebbestad

Keyword(s):

Middle Cambrian ◽

Alum Shale ◽

Shale Formation

Centropleurid trilobites include five genera of which Centropleura Angelin, Anopolenus Salter, Clarella Howell and Luhops Šnajdr are known from eight species in the traditional middle Cambrian (Miaolingian Series, Drumian Stage) of Sweden and Denmark (Bornholm). Beishanella Xiang & Zhang has not been recorded in Scandinavia so far, and no centropleurids have been reported from Norway. Of these taxa, only Centropleura is common in Scandinavia. Two pygidia previously identified as Centropleura sp. and Anopolenus sp. from erratics in Germany and Bornholm, respectively, as well as a new pygidum from Scania in Sweden are here identified as Anopolenus henrici Salter. Elsewhere, the species is known from Wales, Avalonian Canada, Siberia, Alaska, and Sardinia, occurring in the A. atavus and P. punctuosus zones (the former in Siberia only). The presence of this species increases the known diversity of Centropleuridae in Scandinavia and is important for correlation between Baltica and Avalonia.

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Yuepingia? sp., a ceratopygid trilobite from the upper Cambrian (Furongian) of Scandinavia

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-2010-58-03 ◽

2010 ◽

Vol 58 ◽

pp. 29-33

Author(s):

Thomas Weidner ◽

Arne Thorshøj Nielsen

Keyword(s):

East Coast ◽

Upper Cambrian ◽

South Central ◽

Alum Shale ◽

Shale Formation

A single pygidium found in an ice-rafted loose boulder of coquinoid bituminous limestone represents an ‘exotic’ trilobite hitherto unknown from the Scandinavian Alum Shale Formation. The limestone, found on the east coast of Jutland, Denmark, also contains Leptoplastus paucisegmentatus, Parabolina spinulosa and Orusia lenticularis and derives from the upper Cambrian (Furongian) Leptoplastus paucisegmentatus Zone of Västergötland, south-central Sweden. The ‘exotic’ pygidium shows closest resemblance to the ceratopygid Yuepingia glabra, described from Alaska, and is treated as Yuepingia? sp. The Laurentian Y. glabra occurs in the Ptychaspis-Prosaukia Zone which corresponds in age to the Scandinavian Leptoplastus Superzone.

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Stratigraphy and geochemical composition of the Cambrian Alum Shale Formation in the Porsgrunn core, Skien–Langesund district, southern Norway.

Bulletin of the Geological Society of Denmark ◽

10.37570/bgsd-2018-66-01 ◽

2018 ◽

Vol 66 ◽

pp. 1-20

Author(s):

Niels Hemmingsen Schovsbo ◽

Arne Thorshøj Nielsen ◽

Andreas Olaus Harstad ◽

David L. Bruton

Keyword(s):

Gamma Ray ◽

Geochemical Composition ◽

Middle Cambrian ◽

Alum Shale ◽

Carbon Isotope Excursion ◽

Lower Ordovician ◽

Shale Formation ◽

Sedimentary Succession ◽

Southern Norway ◽

Spice Event

The fully cored BHD-03-99 borehole (hereafter referred to as the Porsgrunn borehole and core) penetrated Ordovician and Cambrian strata in the Skien–Langesund district, southern part of the Oslo region in Norway. Hand-held X-ray fluorescence (HH-XRF) measurements combined with spectral gamma ray and density core scanning of the Middle Cambrian – Furongian Alum Shale Formation have been made and compared with similar measurements obtained on Alum Shale cores from Scania (southernmost Sweden) and Bornholm (Denmark). The Porsgrunn drill site is located in an area that was only mildly overprinted by Caledonian tectonics and represents one of the few sites in the Oslo area where a nearly untectonised sedimentary succession can be studied in terms of thickness and geochemistry. The Alum Shale Formation is 28.8 m thick in the Porsgrunn core, excluding the thickness of five 0.9–5.5 m thick dolerite sills of assumed Permian age. In the Alum Shale Formation the bulk densities are around 2.7 g/cm3 with a slightly decreasing trend up through the formation. The shale has total organic carbon (TOC) values up to 14 wt%, which is comparable to the TOC levels for the Alum Shale elsewhere in the Oslo area and for dry gas matured Alum Shale in Scania and Bornholm. The basal Furongian is characterised by a gamma ray low and an increase in Mo interpreted to reflect the Steptoean Positive Carbon Isotope Excursion (SPICE) event. The Porsgrunn core data suggest that the Mo concentration remained high also after the SPICE event. Characteristic, readily identified features in the gamma log motif are named the Andrarum gamma low (AGL), base Furongian gamma low (BFGL), Olenus triple gamma spike (OTGS) and the Peltura gamma spike (PGS). No Lower Ordovician Alum Shale is present. The 14.8 m thick Furongian part of the Alum Shale represents the Olenus, Parabolina, Leptoplastus, Protopeltura and Peltura trilobite superzones judging from log-stratigraphic correlations to Scania and Bornholm. The Middle Cambrian interval is 14.0 m thick and includes the Exsulans Limestone Bed and 1.4 m of quartz sandstone. A 0.3 m thick primary limestone bed may be an equivalent to the Andrarum Limestone Bed. The succession represents the Paradoxides paradoxissimus and P. forchhammeri superzones. The Alum Shale Formation rests atop the 13.0 m thick Lower Cambrian Stokkevannet sandstone (new informal name) that in turn directly overlies the basement. Overall, the stratigraphic development of the comparatively thin Alum Shale Formation resembles the condensed sequence seen on Bornholm.

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Integration of the outcrop and subsurface geochemical data: implications for the hydrocarbon source rock evaluation in the Lower Indus Basin, Pakistan

Journal of Petroleum Exploration and Production Technology ◽

10.1007/s13202-018-0569-6 ◽

2018 ◽

Vol 9 (2) ◽

pp. 937-951 ◽

Cited By ~ 1

Author(s):

Sajjad Ahmad ◽

Faizan Ahmad ◽

Abd Ullah ◽

Muhammad Eisa ◽

Farman Ullah ◽

...

Keyword(s):

Organic Matter ◽

Source Rock ◽

Vitrinite Reflectance ◽

Indus Basin ◽

Hydrocarbon Generation ◽

Type Ii ◽

Hydrocarbon Source Rock ◽

Hydrocarbon Generation Potential ◽

Well Data

Abstract The present study details the hydrocarbon source rock geochemistry and organic petrography of the outcrop and subsurface samples of the Middle Jurassic Chiltan Formation and the Lower Cretaceous Sembar Formation from the Sann #1 well Central and Southern Indus Basin, Pakistan. The total organic carbon (TOC), Rock–Eval pyrolysis, vitrinite reflectance (Ro) % and Maceral analysis techniques were used and various geochemical plots were constructed to know the quality of source rock, type of kerogen, level of maturity and migration history of the hydrocarbons. The outcrop and Sann #1 well data on the Sembar Formation reveals poor, fair, good and very good quality of the TOC, type II–III kerogen, immature–mature organic matter and an indigenous hydrocarbon generation potential. The outcrop and Sann #1 well data on the Chiltan Formation show a poor–good quality of TOC, type II–III kerogen, immature–mature source rock quality and having an indigenous hydrocarbon generation potential. The vitrinite reflectance [Ro (%)] values and Maceral types [fluorescent amorphous organic matter, exinite, alginite and inertnite] demonstrate that maturity in both Sembar and the Chiltan formation at surface and subsurface fall in the oil and gas generation zone to cracking of oil to gas condensate zone. Recurrence of organic rich and poor intervals within the Sembar and Chiltan formation are controlled by the Late Jurassic thermal uplift preceding the Indo-Madagascar separation from the Afro-Arabian Plate and Early Cretaceous local transgressive–regressive cycles. From the current study, it is concluded that both Sembar and Chiltan formation can act as a potential hydrocarbon source rock in the study area.

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