The Huai Hin Lat Formation has a high-potential resource, and the Ban Nong Sai part was researched and sampled. To achieve this goal, petrographic analysis (kerogen types), geochemical analysis ...(total organic carbon content, TOC), vitrinite reflectance (R
o
), and Rock–Eval (RE) pyrolysis were carried out in this study. According to the findings, types II, III, and IV were identified using a modified Van-Krevelen diagram because the higher mature source rock showing hydrogen index (HI) and oxygen index (OI) are continuously depleted and raised. However, microscopic observation describes macerals as primarily sapropelic amorphinite, therefore, type I is important. The TOC was determined to be between 1.90% and 7.06%, which is considered very good to excellent. The original total organic carbon (TOC
o
) was decided to use its maceral components to determine how to convert extremely mature TOC to TOC
o
. It varies between 5.13% and 10.74% and reaches a maximum of 57.21% which is comparable to TOC. At 0.82%–1.04%, 443–451 °C, 0.50%–38.10%, and 69.00%–99.59% are the vitrinite reflectance (R
o
), maximum temperature (T
max
), production index (PI), and transformation ratio (TR), respectively. Late peak maturity refers to a mixture of oil and gas, whereas most TR ratios refer to the main gas phase. Similarly, the petroleum residual shows no indication of gas trapped at a volume of 6309.50 mcf/ac-ft. In summary, source rock potential was assessed within a suitable risk range defined by T
max
(445.70 °C), R
o
(0.91%), TR (90.63%), TOC (8.15%), shale thickness (46 m), and kerogen type (type I).
The Whitehill Formation (WHF) is part of the organic-rich black shales deposited in the shallow seas that occurred within the continental interior of southwest Gondwana during the Lower Permian and ...has been identified as the main potential shale gas reservoir in South Africa. Here, high-resolution total organic carbon (TOC) content, organic petrographic composition, and multiple geochemical studies conducted on samples of the WHF in peak oil to gas maturity (vitrinite reflectance, Ro, range between 0.98 and 1.26%) were used to evaluate the influence of relative sea-level and climatic fluctuations on paleoproductivity, bottom-water redox condition, and clastic supply, and their combined control on the stratigraphic distribution of TOC content and macerals. Organic petrographic observations and geochemical data allowed recognition of three stratigraphic intervals (ORI-1 to ORI-3) that show marked differences in TOC content and maceral type, as well as mineralogical composition and submillimeter-to centimeter-scale sedimentary textures. TOC content increases from 0.93% at the base to 16.75% at the top. Data further revealed that the lower interval (ORI-1) is dominated by organic macerals biologically produced in the water column, including algal Tasmanites cysts, spores, and radiolaria, and depleted in land-derived macerals (inertinite, vitrinite). The mid (ORI-2) and upper ORI-3) intervals are shown to be composed of both production-derived components including bacterial biomass and aquatic plants (algae and radiolaria), as well as land-derived macerals, which are intermixed with clay-sized mineral particles, forming interconnected algal/bacterial mats. Trace and major element data indicate that these stratigraphic variations and heterogeneity of both TOC content and maceral reflect the variability of paleoproductivity, redox conditions, and clastic supply, which in turn were influenced by fluctuations of relative sea level and climate. Specifically, the accumulation of ORI-1 occurred during sea-level highstand and cool-climate, resulting in relatively higher paleoproductivity, reduced bottom-water oxygenation, and low clastic supply. However, pervasive degradation of organic matter at the seabed occasioned by low clastic detritus resulted in lower TOC content. Moreover, reduced supply of clastic detritus and severe organic matter degradation diminished the sizes of telalginite and the concentration of macerals into interconnected networks. On the contrary, intermittent decreases of relative sea-level (shallowing) and warmer conditions were detected in the mid and upper intervals, and the associated buildup of clastic sediment enhanced organic matter burial. Together these conditions resulted in higher TOC and better preservation of labile macerals. To conclude, the scale of stratigraphic heterogeneity of both TOC content and maceral type reported here may be present in many other black shale successions. Therefore, this type of study should constitute a fundamental step in the characterization of shales for their unconventional oil/gas reservoir potential.
•Sea-level fluctuations control productivity, clastic supply, and bottom-water redox.•Organic content in shales can be tied to a sequence stratigraphic context.•Maximum organic content may not coincide with sea-level highstand.•This type of study is fundamental to the evaluation of shales as oil/gas reservoirs.
This study investigates the paleodepositional conditions of the No. 6 Seam of the Madzaringwe Formation in Makhado and Voorburg south area of the Soutpansberg Coalfield (Limpopo Province, South ...Africa) utilizing organic petrography and inorganic geochemical proxies. The coals are predominantly high-volatile bituminous B-A rank with high ash yields (avg. 36.1 wt%), characterized by high-vitrinite (~ 41.5 vol%), moderate-to-high inertinite (9.8 vol%–33.7 vol%) and low liptinite (~ 2.3 vol%). The distribution of inertinite varies among different coal horizons (from bottom-lower to middle-upper), suggesting differential oxidation conditions and/or paleofire occurrence. Vitrinite-to-inertinite (V/I) ratio, tissue preservation–gelification index (TPI–GI), and groundwater–vegetation index (GWI–VI) plots, indicate that the peat-forming forest-swamp vegetation accumulated under mesotrophic-to-rheotrophic hydrological conditions. The presence of structured macerals (i.e., telinite, collotelinite, fusinite, and semifusinite) suggests well-preserved plant tissues, whereas framboidal pyrite and sulphur content (0.24 wt%–2.16 wt%) point to brackish-water influence at the peat stage. The coals contain quartz, kaolinite, siderite, muscovite, dolomite, calcite, and pyrite minerals, most of which were likely sourced from felsic igneous rocks. The Al/(Al+Fe+Mn) and (Fe+Mn)/Ti ratios for the studied samples range between 0.24–0.97 and 0.57–70.10, respectively. The ratios, Al–Fe–Mn plot, and presence of massive botryoidal-type pyrite imply some influence of meteoric waters or fluids from hydrothermal activity post-deposition. Moreover, the chemical index of alteration (CIA: 98.25–99.67), chemical index of weathering (CIW: 92.04–97.66), and A–CN–K ternary diagram suggest inorganic matter suffered strong chemical weathering, indicating warm paleoclimatic conditions during the coal formation.
Black shales outcropping in the Douala Basin were studied using organic petrography and Rock-Eval pyrolysis. The goal of this study was to use organic petrography and bulk geochemical analysis to ...evaluate N'kapa Formation shales in terms of organic matter (macerals) composition and its relationship to oil and gas productivity potentials. The quantity of organic matter, kerogen type and thermal maturity were determined, and their relationship to oil and gas generation was evaluated. The results of this investigation indicate that the nine samples analyzed had average random vitrinite reflectance values (VRo random) between 0.48 and 0.57% and are indicative of immature source rocks. Calculated maximum reflectance values (VRo maximum) ranged from 0.50 to 0.59%, showing a maximum volatile C bituminous rank and Liptinite macerals were found to fluoresce in the yellow-green to the yellow range, which is consistent with the indicated rank. The total organic carbon (TOC) of the samples ranges from 0.55 to 2.23 wt% (average of 1.18 wt%), implying fair to good concentration of organic matter, while the S1 values range from 0.04 to 0.10 mg HC/g rock (average of 0.07 mg HC/g rock) and S2 values range from 0.10 to 0.91 mg HC/g rock (average of 0.38 mg HC/g rock) and are described as showing poor source potential. Based on Genetic Potential (GP = S1+S2) values (0.18-1.01 mg HC/g rock), the studied N'kapa Formation shales are dominated by type III gas-prone kerogen with a minor association of type IV kerogen. The hydrogen index (HI<50mg HC/g TOC) and oxygen index (OI<75mg CO2/g TOC) values are too low for the shales to have generated hydrocarbons. The low values HI and OI and the absence of type II and mixed type II/III may be due to some degree of weathering of the samples.
Silurian graptolite shales from an exploration borehole within the Baltic Basin (N-Poland) were examined by the electron microprobe (for the first time) and micro-FTIR spectroscopy. The graptolite ...periderm of mean reflectance Rr ≈ 1.30–1.80% (VRE ≈ 1.10–1.50%) contains ~85–91 wt% of carbon, 2.5–8.5 wt% of oxygen, 1.5–3 wt% of nitrogen and (by difference) ~3.0–4.5 wt% of hydrogen. Aromatic structures predominate, with minor amounts of the aliphatic and carbonyl groups. Carbon content in the graptolite periderm increases and oxygen content decreases with the increasing depth and mean reflectance (Rr). This is accompanied by the increase in aromaticity of the structure and shortening of the aliphatic chains. The studied graptolites represent mostly kerogen type II and, partly, type III. Chemical structure of the graptolite periderm reveals many similarities to that of vitrinite of the adequate rank (considering the Vitrinite Reflectance Equivalent values).
•Graptolite periderm (Rr ≈ 1.30–1.80%) studied by the electron microprobe for the first time.•It contains ca. 85–91 wt% of C, 2.5–8.5 wt% of O and 1.5–3 wt% of N.•Aromatic structures predominate, with minor amounts of the aliphatic and carbonyl groups.•Graptolite periderm represents mostly kerogen type II, and partly type III.•Similarities found in the chemical structure of the graptolite periderm and vitrinite.
This paper investigates chemical functional groups of the two extracted bitumen fractions in shales of the Jurassic to early Cretaceous Vaca Muerta Formation of the Neuquén Basin in Argentina, South ...America. The results indicate that Bitumen I is strongly aliphatic and appears to be genetically related to fluorescent amorphous organic matter. In contrast, Bitumen II consists of highly condensed, aromatic hydrocarbons, and has some correspondence to nonfluorescent amorphous organic material. Comparison of Rock-Eval VI pyrolysis data (S1 and S2) with the bitumen yields suggests that Bitumen I relates to S1 but also to S2. In addition, Bitumen I has a positive correlation with light liquid hydrocarbons (C5–C29), but also partially with heavier hydrocarbons (above C30). This suggests that Bitumen I corresponds to the majority of lighter hydrocarbons up to C29 and some portion to heavier hydrocarbons. These results have implications for the assessment of the mobility of generated hydrocarbons and their availability for production.
•Vaca Muerta shale is highly heterogeneous and exhibits strong geochemical variations.•Extracted Bitumen I & Bitumen II fractions are chemically different.•Bitumen I and Bitumen II show relationship with fluorescent and non-fluorescent macerals, respectively•Bitumen I has better mobility than Bitumen II, facilitating oil production
Detailed Fourier Transform Infrared Spectroscopy (FTIR), chemical oxidation and reduction, and multivariate regression analysis have been applied to gain insight into the relative proportions and ...types of oxygen functional groups in coals of varying rank and in alginite-rich organic matter in oil shales and marine shale. FTIR spectra of demineralised and non-demineralised coals with a vitrinite reflectance below ~
0.4%
R
o revealed that the spectra are significantly different in the carbonyl region, probably due to the configuration of weak conjugated oxygen bonds into a more rigid form during demineralisation. In coals and lignin, the relative FTIR response from oxygen groups occurs in the order hydroxyl
≥
ether
>
ketone/ester
>
carboxyl
>
quinone, where ester groups are related to cutinite and sporinite. A pronounced decrease in oxygen content occurs from ~
0.43–0.50%
R
o, but the oxygen groups show different evolutionary trends during initial thermal maturation: (i) carboxyl group absorption increases significantly up to lignite/subbituminous C rank, followed by a rapid decrease and disappearance at ∼
0.45%
R
o, (ii) ketone (carbonyl) group absorption is prominent at maturities <
0.45%
R
o, but at higher maturities the response declines gradually, (iii) ether group absorption increases to a maximum at ∼
0.45–0.50%
R
o, from where it decreases gradually, (iv) at atomic O/C ratios >
0.2 (approximately <
0.45%
R
o) hydroxyl group (principally phenolic) absorption is highly variable, but at increasing thermal maturity significant dehydroxylation occurs. Elimination of oxygen groups in the coaly organic matter thus occurs in the order quinone, carboxyl, ketone/ester, hydroxyl and ether. Both ether and hydroxyl are still present at an O/C ratio of 0.05. Oxygen in the alginite-dominated kerogen of the shales is entirely bound as ether, carbonyl (mainly ester) and hydroxyl. The presence of ether agrees with the dominant role of ether bonds cross-linking long-chain
n-alkanes in algaenan. Hydroxyl may be related to phenolic units in for example
Botryococcus algae. The relative FTIR response from oxygen groups in kukersite is ether
>
carbonyl (ketone)
>
hydroxyl, which generally reflects the structural models proposed for kukersite. Oxygen groups in the coals can overall be correlated to the least-altered huminite macerals textinite, texto-ulminite, and densinite, or to the associated cutinite and sporinite, whereas the variation of the oxygen group composition in the studied shales seems to be controlled by thermal maturity. Hydrogen Index (HI) values of chemically oxidised and/or reduced coal samples do not provide an unequivocal answer to whether HI values of immature coals are underestimated. Incorporation of carboxyl groups into the original coal kerogen does not produce a more immature coal manifested by decreased HI values.
•Complexity of coal demands increasing spatial resolution in characterization.•Scanning probes offer various spatially-resolved characterization functionalities.•Coal samples were imaged with ...micro-Raman and Scanning Microwave Microscopy.•This combination allowed resolving coal structure below a 100-nm spatial resolution.
Structural complexity and variability of the chemical properties define technological applicability of coal and demand increasing accuracy and spatial resolution from the techniques used for coal characterization for development of new, clean, and efficient technologies of coal utilization. Here, we combined spatially-resolved reflectometry, fluorescence, and confocal micro-Raman spectroscopy with high-resolution scanning probe microwave imaging to achieve a nondestructive sub-100-nm spatial resolution mapping of coal structure. It was found that this approach allows for high spatial resolution identification of individual elements in coal architecture, thus potentially generating valuable input for knowledge-driven optimization and design of coal utilization processes.
The present study focuses on the investigation of the optical anisotropy, optical sign, textural heterogeneity and deformational features of the maceral grains along with the Raman spectral ...characteristics of the seven coal samples collected from the Himalayan fold-thrust belts of Sikkim State, India. The coal samples were extremely fragile and pulverized due to the intense tectonic deformation. The maceral composition revealed the dominance of semifusinite over collotelinite grains. The calculated maximum vitrinite reflectance (5.94–8.66%) and mean random reflectance (4.11–5.36%) suggest anthracite A rank of the coal samples following ISO 11760:2005. The proximity of the intermediate reflectance axis value (RINT) to maximum reflectance axis value (RMAX) as well as the range of Reflectance Indicating Surface (RIS) style (Rst) values (−9.98 to −19.37) indicates the biaxial negative optical texture of the vitrinite grains. The augmented bireflectance values due to enhancement of the RMAX associated with strong decline in RMIN may suggest the commencement of pregraphitization. In addition, the strong linear correlation (r = 0.94) of the RIS-anisotropy (Ram) parameter with the bireflectance values may imply the role of tectonic stress on the optical transformations of the samples. The range of the peak temperature (334.94–369.01 °C) calculated from mean random vitrinite reflectance may suggest the effect of thermo-stress coupling on the metamorphism of these coal samples. Microlithotype study combined with deformational aspects of macerals shows the presence of “deformed”, “sheared” and “smashed” grains within each sample, which may, additionally, document the tectonic stress influence on the coal particles. Moreover, relatively, larger area of ‘defect band 1 (D1)’ than that of ‘graphitic band (G)’ along with the broad G band in the first order Raman spectra may indicate the considerable presence of structural dislocations and aromatic compounds with disordered bond angle within the microstructure induced by the tectonic deformation. The lowest intensity of the ‘defect band 4 (D4)’ may suggest the preferential removal of aliphatic compounds from the samples in response to the tectonic stress degradation. In addition, the relative area ratio calculated from the D1 and the G bands (AD1/(AD1 + AG)) may indicate that the studied anthracite samples would have attained the metamorphic temperature ranging from 325.12–387.89 °C.
Display omitted
•Anthracite A samples from Rangit window of Sikkim Himalayan fold-thrust belts.•Enhanced bireflectance and onset of pregraphitization.•Biaxial negative optical texture and high magnitude of anisotropy of vitrinite.•High AD1/AG ratio and wide G band implying presence of micro-structural disorders.•Metamorphic temperature attained up to 387.89 °C.
The peculiar characters and industrial applications of carbon nanotubes (CNTs) and carbon nanoballs (CNBs) have attracted the interests of technologists, scientists, and policy-makers. Here, authors ...have synthesized CNTs and CNBs through MCL (molten caustic leaching) method from ten coal samples belonging to Ib valley Basin, Odisha, India. HRTEM (High-Resolution Transmitted Electron Microscopy), FTIR (Fourier Transform Infrared) spectroscopy and XRD (X-ray Diffraction) analyses appraised the presence of carbon nano-particles with varied sizes in the MCL products. The nanoballs are in the range of 52-64 nm and the nanotubes are within the range of 7-15 nm in diameter. The petrographic parameters viz. various macerals and rank, as well as a measure of aliphatic bonds, have a significant impact on the amount of yield, purity, and quality of CNTs/CNBs. Carbon nano-products (CNPs) yield is increased with the fixed carbon content and decreased with volatile matter yield and mineral matter present in coals. Oxygen and hydrogen content in coal have decreased the carbon nano-products yield. Optical microscopic study of coals revealed that the carbon nano-products (CNPs) formation is favored with an increase in vitrinite and liptinite and decrease with inertinite macerals. Inertinite macerals, characterized by high aromaticity with aromatic rings of large size, do not take part (little participation) in reaction with alkalies and in acid treatment. The aliphatic bonds and chains in liptinites and vitrinites help in carbon nano-products synthesis. The proposed empirical equation PEC (petrographic estimate of CNPs) seems to indicate the amount of CNPs yield through the MCL process. The MCL may be a proficient technique for the synthesis of nano‑carbons as well as the removal of mineral matter from coals.
Display omitted
•Maceral and mineral reactivity in CNPs (carbon nano-products) development•PEC (petrographic estimate of CNPs) predicts the amount of CNPs yield.•Vitrinite and liptinite favor CNPs production•CNPs from bituminous coal through molten caustic leaching (MCL) process•HRTEM of carbon nano-products
PDF