scholarly journals Depositional environment, organic matter characterization and hydrocarbon potential of Middle Miocene sediments from northeastern Bulgaria (Varna-Balchik Depression)

2015 ◽  
Vol 66 (5) ◽  
pp. 409-426 ◽  
Author(s):  
Alexander Zdravkov ◽  
Achim Bechtel ◽  
Stjepan Ćorić ◽  
Reinhard F. Sachsenhofer
Keyword(s):  
Organic Matter ◽  
Middle Miocene ◽  
Depositional Environments ◽  
Hydrocarbon Potential ◽  
Carbonate Sediments ◽  
Terrestrial Organic Matter ◽  
Anoxic Environments ◽  
Moesian Platform ◽  
Rock Eval ◽  
Resistivity Log

Abstract The depositional environments and hydrocarbon potential of the siliciclastic, clayey and carbonate sediments from the Middle Miocene succession in the Varna-Balchik Depression, located in the south-eastern parts of the Moesian Platform, were studied using core and outcrop samples. Based on the lithology and resistivity log the succession is subdivided from base to top into five units. Siliciclastic sedimentation prevailed in the lower parts of units I and II, whereas their upper parts are dominated by carbonate rocks. Unit III is represented by laminated clays and biodetritic limestone. Units IV and V are represented by aragonitic sediments and biomicritic limestones, correlated with the Upper Miocene Topola and Karvuna Formations, respectively. Biogenic silica in the form of diatom frustules and sponge spicules correlates subunit IIa and unit III to the lower and upper parts of the Middle Miocene Euxinograd Formation. Both (sub)units contain organic carbon contents in the order of 1 to 2 wt. % (median: 0.8 for subunit IIa; 1.3 for unit III), locally up to 4 wt. %. Based on Hydrogen Index values (HI) and alkane distribution pattern, the kerogen is mainly type II in subunit IIa (average HI= 324 mg HC/g TOC) and type III in unit III (average HI ~200 mg HC/g TOC). TOC and Rock Eval data show that subunit IIa holds a fair (to good) hydrocarbon generative potential for oil, whereas the upper 5 m of unit III holds a good (to fair) potential with the possibility to generate gas and minor oil. The rocks of both units are immature in the study area. Generally low sulphur contents are probably due to deposition in environments with reduced salinity. Normal marine conditions are suggested for unit III. Biomarker composition is typical for mixed marine and terrestrial organic matter and suggests deposition in dysoxic to anoxic environments.

scholarly journals Changing depositional environments in the semi-restricted Late Jurassic Lemeš Basin (Outer Dinarides; Croatia)

Facies ◽  
2021 ◽  
Vol 68 (1) ◽  
Author(s):  
Michael A. J. Vitzthum ◽  
Hans-Jürgen Gawlick ◽  
Reinhard F. Sachsenhofer ◽  
Stefan Neumeister
Keyword(s):  
Organic Matter ◽  
Deep Water ◽  
Carbonate Platform ◽  
Upper Jurassic ◽  
Depositional Environments ◽  
Source Rocks ◽  
Terrestrial Organic Matter ◽  
Kerogen Type ◽  
Marine Algal ◽  
Rock Eval

AbstractThe up to 450 m-thick Upper Jurassic Lemeš Formation includes organic-rich deep-water (max. ~ 300 m) sedimentary rocks deposited in the Lemeš Basin within the Adriatic Carbonate Platform (AdCP). The Lemeš Formation was investigated regarding (1) bio- and chemostratigraphy, (2) depositional environment, and (3) source rock potential. A multi-proxy approach—microfacies, Rock–Eval pyrolysis, maceral analysis, biomarkers, and stable isotope ratios—was used. Based on the results, the Lemeš Formation is subdivided from base to top into Lemeš Units 1–3. Deposition of deep-water sediments was related to a late Oxfordian deepening event causing open-marine conditions and accumulation of radiolarian-rich wackestones (Unit 1). Unit 2, which is about 50 m thick and Lower early Kimmeridgian (E. bimammatum to S. platynota, ammonite zones) in age, was deposited in a restricted, strongly oxygen-depleted basin. It consists of radiolarian pack- and grainstones with high amounts of kerogen type II-S organic matter (avg. TOC 3.57 wt.%). Although the biomass is predominantly marine algal and bacterial in origin, minor terrestrial organic matter that was transported from nearby land areas is also present. The overlying Unit 3 records a shallowing of the basin and a return to oxygenated conditions. The evolution of the Lemeš Basin is explained by buckling of the AdCP due to ophiolite obduction and compressional tectonics in the Inner Dinarides. Lemeš Unit 2 contains prolific oil-prone source rocks. Though thermally immature at the study location, these rocks could generate about 1.3 t of hydrocarbon per m2 surface area when mature.

Sedimentology, Geochemistry, and Reservoir Potential of the Organic-Rich Tuwaiq Mountain, Hanifa and Jubaila Formations, Abu Dhabi, UAE

2021 ◽  
Author(s):  
Madhujya L. Phukan ◽  
Saad A. Siddiqi ◽  
Abdulla Alblooshi ◽  
Maryam Alshehhi ◽  
Ashis Shashanka ◽  
...  
Keyword(s):  
Organic Matter ◽  
Quantitative Description ◽  
Clay Fraction ◽  
Depositional Environments ◽  
Source Rocks ◽  
Carbonate Sediments ◽  
Pore Scale ◽  
Gas Generation ◽  
Unconventional Gas ◽  
Rock Eval

Abstract Objectives/Scope: The late Callovian to early Kimmeridigian deposited Tuwaiq Mountain, Hanifa and Jubaila Formations are among the most prolific source rocks in the middle east. These sediments have recently been considered as potential unconventional gas reservoir in UAE. This study integrates sedimentological, structural, geochemical and pore-scale datasets to provide a better understanding of the depositional framework and its effects on the reservoir properties. Methods, Procedures, Process: Dunham Classification (1962) which was later modified by Embry & Klovan (1971) is the basis of the descriptive lithofacies scheme used to characterize the organic-rich carbonate sediments. The association of these classified lithofacies based on their genetic relationship reflects their corresponding depositional environments. Petrographical and geochemical assessment including Rock-Eval pyrolysis were performed on selected samples. Mineralogical assessment was performed via whole-rock and clay-fraction XRD analysis, whereas pore-scale fabric/textural investigations were performed via conventional transmitted light microscopy and SEM using backscattered electron mode BS-SEM. Results, Observations, Conclusions: Sedimentological characterization of mud-dominated carbonate sediments indicates that they accumulated in a clastic starved, intrashelf basinal setting. The lack of textural variation is observed, highlighted by the dominance of mudstones noted across the Tuwaiq Mountain Fm., Hanifa and Jubaila Formations. Wackestones are the second most abundant texture observed. Wacke-packstones and packstones are rare but are present in the Tuwaiq Mountain Formation. also dominated by mudstone textures show presence of wackestones in form of thin beds. The occurrences of planktonic foraminifera along with thin shelled bivalves further emphasizes the low-energy, distal depositional setting. A quantitative description of the nature, density, and trends of the fracture network highlights the tectonic and structural history of the sediments. A certain degree of brittleness is associated with the organic-rich sediments, which is evident from the mineralogical analysis showing the abundance of calcite (>82%). Rock-Eval data revealed high TOC content of the sediments. An evaluation of the HI and Tmax indicates that the sediments are dominantly gas prone (HI<150mg HC/g TOC). Based on the calculated reflectance data (Ro: 0.06-3.30), the sediments display varied levels of thermal maturity, from immature to over mature. The vitrinite reflectance equivalent (%VRE) values assessed from microscopic investigations a range between 1.24-1.64, with the lower values suggesting late maturity with wet (condensate) gas generation and the higher values suggesting post maturity with dry gas generation. The TOC and TRA data highlight that the organic-rich, laminated mudstones associated with the Hanifa and Tuwaiq Mountain Formations have the highest TOC values (up to 4.25wt%) and the highest bulk volume (up to 3.39 %BV). It is also noted that the petroleum storage potential in these sediments largely resides with the mineral matrix pores along with the porosity hosted by the organic matter, which has been assessed by BS-SEM analysis. Novel/Additive Information: This integrated approach sheds light on the development of unconventional gas reservoirs. In addition, this study shows how the changes in depositional environment may have controlled the organic matter preservation. For a plausible way forward, this current understanding may be extrapolated to uncored intervals for representativeness.

Geochemistry of the Organic Matter of Ulug-Khem Basin Coals

2021 ◽  
Vol 62 (11) ◽  
pp. 1229-1239
Author(s):  
D.A. Bushnev ◽  
S.A. Ondar ◽  
N.S. Burdel’naya
Keyword(s):  
Mass Spectrometry ◽  
Organic Matter ◽  
Aromatic Hydrocarbons ◽  
Aquatic Vegetation ◽  
Mass Spectrometry Data ◽  
Hydrocarbon Potential ◽  
Gas Liquid Chromatography ◽  
Low Grade ◽  
High Hydrocarbon ◽  
Rock Eval

Abstract —The composition of the organic matter (OM) of coals of the Ulug-Khem Basin has been studied. According to Rock-Eval pyrolysis data, this OM is a type III kerogen, sometimes significantly oxidized. The coal of low-grade metamorphism has a high hydrocarbon potential. Based on the gas–liquid chromatography and chromatography–mass spectrometry data on the distribution of n-alkanes, isoprenoids, polycyclic biomarkers, and aromatic hydrocarbons, we have established the composition of the primary OM of the coals and the grade of OM metamorphism. The primary OM of the coals consists mainly of remains of aquatic vegetation and terrigenous OM. The latter includes conifer remains, which are identified from the presence of 4β(H)-19-norisopimarane in the aliphatic fraction of bitumen and from the domination of retene over cadalene and 6-isopropyl-1-isohexyl-2-methylnaphthalene in the aromatic fraction.

Tracing terrestrial organic matter in surface sediments in Laptev Sea and East Siberian Sea: a Rock-Eval pyrolysis approach

2020 ◽  
Author(s):  
Elena Gershelis ◽  
Roman Kashapov ◽  
Alexey Ruban ◽  
Andrey Grin'ko ◽  
Oleg Dudarev ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Surface Sediments ◽  
The Arctic ◽  
Laptev Sea ◽  
Residual Carbon ◽  
Terrestrial Organic Matter ◽  
East Siberian Sea ◽  
Carbon Compounds ◽  
Rock Eval

<p>The East Siberian Arctic shelf (ESAS), the world’s largest continental shelf, receives substantial input of terrestrial organic carbon (TerrOC) both from increasing river discharge and from amplifying coastal erosion. Increasing TerrOC supply directly affects the Arctic marine carbon cycle, and, therefore, the fate of TerrOC upon its translocation to the Arctic continental margin has been the subject of growing interest in recent decades. Previous studies reported a strong decrease in sedimentary bulk TerrOC and terrestrial biomarkers with increasing distance from the coast during cross-shelf transport with much higher extent of degradation in the ESAS nearshore zone. Despite major progress has been made in estimating TerrOC inputs and quantifying its degradation rates in the Arctic land-shelf system, there are still important pieces insufficiently understood. Rock-Eval (RE) pyrolysis contributes to the traditional geochemical interpretations, based on elemental, isotopic and biomarker analyses and provides additional insight into the distribution, source and degradation state of organic carbon compounds of sedimentary organic matter.</p><p>In this study, the analytical approach included the characterization of marine and terrestrial carbon compounds using RE data coupled with organic carbon stable isotope composition. Rock-Eval analyses was performed on over 80 surface sediments samples from the Laptev Sea and western part of the East Siberian Sea collected during Arctic expeditions in 2011-2019. A track of rapidly degrading terrOC in shallow deposits may be traced using the ratios between hydrogen and oxygen indices and from the distribution of labile organic carbon fraction. Our results indicated high content of heavily degraded material with low hydrogen index, high oxygen index and a high content of residual carbon in sediments on the outer shelf of the western Laptev Sea and on the continental slope. Sharp decreasing of oxygen content in the eastern part of Laptev Sea and the western East Siberian Sea marked intensive dilution of degraded carbon with fresher material exported from New Siberian Islands. Furthermore, the RE data indicated a relatively high content of residual carbon (up to 87 %) stored in the studied surface sediments.</p><p>This research is supported by Russian Science Foundation, project # 19-77-00067.</p>

scholarly journals Carbon and Nitrogen Cycle Dynamic in Continental Late-Carboniferous to Early Permian Basins of Eastern Pangea (Northeastern Massif Central, France)

2021 ◽  
Vol 9 ◽  
Author(s):  
Mathilde Mercuzot ◽  
Christophe Thomazo ◽  
Johann Schnyder ◽  
Pierre Pellenard ◽  
François Baudin ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Black Shales ◽  
Depositional Environments ◽  
Late Carboniferous ◽  
Type I ◽  
Early Permian ◽  
Massif Central ◽  
Carbon And Nitrogen ◽  
Rock Eval

Late Carboniferous to early Permian organic-rich sedimentary successions of late-orogenic continental basins from the northeastern Massif Central (France) coincide with both the Variscan mountain dismantling and the acme of the long-lasting Late Paleozoic Ice Age. Here, we investigate the carbon and nitrogen cycles in the newly dated sedimentary successions of the Decize–La Machine and Autun basins during these geodynamic and climate upheavals. The sedimentary organic matter has been analyzed through Rock-Eval pyrolysis, palynofacies and elemental and isotope geochemistry along cored-wells and outcropping sections, previously accurately defined in terms of paleo-depositional environments. Rock-Eval and palynofacies data have evidenced two origins of organic matter: a phytoplanktonic/bacterial lacustrine origin (Type I organic matter, organic δ13C values around −23.5‰), and a terrestrial origin (vascular land plants, Type III organic matter, organic δ13C values around −20‰), mixed in the deltaic-lacustrine sediments during background sedimentation (mean organic δ13C values around −22‰). Episodes of high organic matter storage, reflected by black shales and coal-bearing deposits (total organic carbon up to 20 and 70%, respectively) are also recognized in the successions, and are characterized by large negative organic carbon isotope excursions down to −29‰. We suggest that these negative isotope excursions reflect secondary processes, such as organic matter remineralization and/or secondary productivity varying under strict local controls, or possibly larger scale climate controls. At times, these negative δ13C excursions are paired with positive δ15N excursions up to +10‰, reflecting water column denitrification and anammox during lake-water stratification episodes. Together, these isotopic signals (i.e., low sedimentary organic δ13C associated with high bulk δ15N values) indicate periods of high primary productivity of surface waters, where nitrogen and carbon cycles are spatially decoupled. These local processes on the sedimentary isotope archives may partially blur our ability to directly reconstruct paleoclimate variations in such continental settings using only C and N isotopes. At last, we explore an organic δ13C-based mixing model to propose ways to disentangle autochthonous versus allochthonous origin of organic matter in lacustrine continental settings.

scholarly journals Evaluation of the hydrocarbon generation potential of the Pimenteiras Formation, Parnaiba Basin (Brazil) based on total organic carbon content and Rock-Eval pyrolysis data

2020 ◽  
pp. 014459872094958
Author(s):  
Agostinho Mussa ◽  
Wolfgang Kalkreuth ◽  
Ana Maria Pimentel Mizusaki ◽  
Marleny Blanco González ◽  
Tais Freitas da Silva ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Total Organic Carbon ◽  
Depositional Environments ◽  
Organic Carbon Content ◽  
Hydrocarbon Generation ◽  
Burial History ◽  
Anoxic Conditions ◽  
Rock Eval ◽  
Parnaíba Basin

The Parnaiba Basin is a Paleozoic to Mesozoic intraplate volcano-sedimentary basin where the Pimenteiras Formation (Devonian) is the main sequence with potential of hydrocarbon generation, mostly natural gas. The present paper evaluates the potential of hydrocarbon generation of Pimenteiras Formation based on Total Organic Carbon (TOC) and Rock-Eval pyrolysis parameters. In this work, 1077 shale samples of the Pimenteiras Formation distributed in 32 wells were evaluated. The TOC content varies between 0.1 to 4.7 wt.%, partially reflecting the accumulation and preservation rates of the organic matter in marine and coastal depositional environments controlled by regressive-transgressive cycles. The oxic and anoxic conditions vary significantly with deposition in this situation, which were evidenced by HI and OI variations through sample profiles. In the north and center of the basin, the Pimenteiras Formation has a higher potential for hydrocarbon generation relative to the south, probably due to higher anoxic conditions during deposition. The Hydrogen Index indicates the predominance of kerogen types II and III with minor occurrences of types I and IV. The Tmax values indicate general immature conditions and locally postmature, where the lowest temperatures represent the basin´s burial history, whereas the higher ones were influenced by igneous intrusions and thermogenic anomalies related to the Transbrasiliano Lineament. In addition, the excessive heat around the intrusions altered the Rock-Eval pyrolysis parameters as well as the type of organic matter, resulting in a relative increase of the kerogen types III and IV, which explains the great potential for gas generation in this basin.

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