Organic Petrography Analyses Research Articles

Microfacies and Paleomire Reconstruction of Coal in the Warukin Formation, Barito Basin, Kandangan Area, South Kalimantan

Abstract The Barito Basin is one of the basins in South Kalimantan and serves as a coal-producing region. One of the coal-bearing formations present in the Barito Basin is the Miocene Warukin Formation. The purpose of this research is to understand the characteristics of coal macerals, including the dominance of macerals and their microfacies, as well as the type and development of the mire where coal is deposited. This information is crucial for the coal geological study in the Kandangan region, South Kalimantan. The methods employed include organic petrography analysis, proximate and ultimate analysis on seams L8, L5, L5B, M16, and MS02 collected using the ply-by-ply method.The results of the subbituminous coal petrography examination in this formation show the dominance of vitrinite ranging between 41.34-74.04% vol, liptinite between 11.61-38.24% vol, inertinite between 2.21-32.32% vol, and mineral matter ranging from 0.17-1.98% vol, predominantly composed of pyrite. The ash content data ranges from 1.36-15.45 (% wt, adb). The sulfur content data ranges from 0.1-0.45 (% wt, daf). Based on the distribution of maceral abundance, coal microfacies can be categorized into five groups: (1) gelovitrinite-rich group, (2) telovitrinite-rich group, (3) liptinite-telovitrinite-rich group, (4) inertinite-rich group, and (5) telovitrinite-inertinite-rich group. The lower section is predominantly characterized by the telovitrinite-inertinite-rich group. In the middle section, the inertinite-rich group takes precedence, alternating with the liptinite-telovitrinite-rich group. The upper segment is primarily marked by the gelovitrinite-rich and telovitrinite-rich groups. The developed paleomire includes repetitions of topogenous mire and ombrogenous mire. The paleomire type is a wet forest swamp under limnic and telmatic conditions. The dominant original vegetation consists of woody plants, although shrubby plants are also found in significant amounts. Moderate to high gelification levels indicate that the peat was constantly inundated with water.

From land to sea: provenance, composition, and preservation of organic matter in a marine sediment record from the North‐East Greenland shelf spanning the Younger Dryas–Holocene

The organic matter content of marine sediments is often used to infer past changes in ocean conditions. However, the organic carbon pool preserved in coastal sediments is a complex mixture derived from different sources and may not reflect in situ processes. In this study, we combine taxonomic identification of reworked palynomorphs with pyrolysis organic geochemistry and reflected‐light organic petrographic microscopy to investigate the provenance, composition and preservation of organic matter in a marine sediment core retrieved from the NE Greenland shelf. Our study reveals continuous yet variable input of land‐derived organic carbon to the marine environment throughout the late Younger Dryas–Holocene, with the highest input of inert carbon in the late Younger Dryas. Although the sediments contain some recent marine palynomorphs, there is no other evidence of fresh marine organic carbon. In contrast, our results indicate that these shelf sediments represent a significant sink of recycled organic carbon. The results of pyrolysis geochemistry revealed that ~90% of the total organic carbon in the sediments is inert. The organic petrography analyses revealed that >70–84% of the organic carbon in the sediment core is terrigenous. Reworked dinoflagellate cysts showed a continuous provenance of Cretaceous land‐derived material, most likely from the nearby Clavering Island. Our study points to the importance of constraining the organic matter origin, composition and preservation in marine sediments to achieve more accurate palaeoenvironmental reconstructions based on organic proxies.

Quantitative evaluation of pore connectivity of shales with a type H3 sorption hysteresis loop

Pore connectivity is a key parameter affecting the hydrocarbon yield of shale reservoirs, and a quantitative study on it is helpful to evaluate the exploration and development potential of shale gas. In this paper, the shales from the Jurassic Yangxia and Kezilenur Formations in the Kuqa Depression, Tarim Basin, China, were taken as an example, and organic petrography analysis, X-ray diffraction analysis, field emission scanning electron microscope (FE-SEM), gas adsorption and helium pycnometry were carried out to determine their petrological, organic geochemical characteristics and pore distribution features. A method for estimating the connectivity of shale with isotherm adsorption curves of a H3 hysteresis loop was established and used to characterize the connectivity of shale pores. The results show that the total pore volume of shale ranges from 2.479 × 10-3 to 20.379 × 10-3 cm3/g, and the specific surface area (SSA) ranges from 1.222 cm2/g to 12.668 cm2/g. The samples’ coordination number (Z) is between 1.215 and 3.064, and the percolation cluster length (L) is between 2.429 and 3.859. Shale with more micropores or higher TOC has a larger Z value, indicating that organic matter pores and micropores have better connectivity. There is no correlation between Z and Tmax, meaning that the effect of maturity on Z is insignificant. The impact of TOC on the L value is also not substantial. Besides, Tmax and illite content show a negative correlation with L, indicating that the high maturity and illite content impede the development of the percolation cluster.

Geochemical and organic petrographic analyses on the Late Eocene bentonitic shale bed in Kom Aushim vicinity, Fayum, Egypt; Paleoenvironmental implications

Bentonitic shale bed of the Qasr El Sagha Formation (Late Eocene), located in the Kom Aushim area, Fayum, composes of 5 m thickness of dark massive stratum intercalated with veins of iron bands. In this study, twelve fresh shale samples from this area were investigated concerning their geochemical and organic petrography analyses. A total organic carbon (TOC) of the shale samples is very low (0.07–0.39 wt%). Petrographic analysis of samples shows a dominance of the vitrinite maceral followed by either inertinite and/or liptinite macerals. Theoretically derived vitrinite reflectance (Rocal) reveals that the bentonitic shale bed was subjected to an abnormal increase in maturity toward the invasion of Fe, Zn, Cu rich hydrothermal sulfates and oxides veins. The composition and origin of these veins were investigated by XRD and XRF analyses. The results suggested that the Fe brought from these veins affected the main composition of the shale stratum to exhibit Fe-shale facies. Moreover, rich iron in the depositional medium leads to form siderite minerals (≈10%) and the replacement of lime associated clay to Ferron dolomite (≈25%). The dominant paleoclimate synchronized shale deposition was semi-arid and arid climate, as confirmed by the domination of evaporite (≈44% gypsum). The source area of shale components was found to be sedimentary and mafic igneous (basaltic trend). CIA-ICV and A–CN–K ternary diagrams showed that the shale components were subjected to a variety of intensive to moderate weathering, and they were probably coming from gabbro and tonalite igneous rock. An active sedimentary margin and island arc are the main provinces, as the shale was deposited at the marine anoxic condition of a clay-lime platform of a pro-delta sedimentary setting. The organic matters (OM) are of type III and IIIC that refer to terrestrial OM of marginal aquatic environments. Organic and inorganic studies confirm a prevailing depositional environment of a shallow shelf, shoreline mudflats and evaporitic lagoon that reflects the general trend of sea-level regression in the Fayum area during the Late Eocene.

Hydrocarbon generation potential of Chichali Formation, Kohat Basin, Pakistan: A case study

The Chichali Formation encountered in Chanda 01 well, located in the Shakardara Kohat, Khyber Pakhtunkhwa Province of Pakistan has been studied in detail as a source for hydrocarbon. Nine drill cuttings of the formation were subjected to geochemical analyses and organic petrography. Various screening techniques including TOC analysis by using Leco-CS analyzer, Rock Eval pyrolysis and organic petrography were used to determine the quality, quantity, maturity and depositional environment of the organic matter. The total organic carbon (TOC) of samples from Chichali Formation ranging from 0.47 to 2.76 wt% indicate fair to very good source rock. Pyrolysis parameters resulted in S1values ranging from 0.21 to 0.83 mg/g of rock, S2 0.44 to 0.61 mg/g rock, PI 0.32–0.51 and Tmax 442–448 °C. The Tmax and vitrinite reflectance data (0.72–0.84 Ro %) indicate that Chichali Formation is effective source rock and is in the process of generating hydrocarbons and falls within oil window. Geochemical parameters Hydrogen index (HI), Oxygen index (OI), Tmax along with organic petrography analyses (maceral) are used for kerogen type evaluation. The calculated HI ranges between 31 and 54 mg HC/g TOC and OI 30–96 mg O2/g TOC. Using modified Van Krevlen diagram between HI vs OI of Rock Eval pyrolysis and maceral analyses, kerogen type II/III and transition between anoxic to oxic depositional environments is interpreted for the studied Chichali Formation.

Comparative petrography and organic geochemistry of different types of organic matter occurring in the Outer Carpathians rocks

The characterization of organic matter (OM) in sedimentary rocks is important in many types of biological, geological and environmental research. The integrated use of microscopy and geochemistry, as here, is particularly useful in any attempt to define the origin and evolution of OM in sedimentary basins. The organic petrography and geochemistry different types of allogenic and authigenic OM from the Polish Outer Carpathian (POC) rocks were studied in present study to compare their genetic type, thermal maturity, depositional environment and post-sedimentation processes. Special attention was paid to redeposited coal clasts occurrences. The used techniques show differences in organic matter type originating from various sources. The organic petrography analysis shows that redeposited coal clasts (CC) and terrigenous organic matter (TOM) are composed predominantly of woody material (the gas-prone Type-III kerogen). Similar results were obtained during the Rock-Eval pyrolysis. Moreover, the GC-MS analysis of extracts indicated the additional source of OM, namely planktonic organic matter (POM) with oil-prone kerogen Type-I or II. This OM is in some cases high thermally mature and could potentially has allochthonous origin. The n-alkane, saturated and aromatic biomarker data revealed deposition of this POM in anoxic deltaic or close-shore sedimentary environments whereas the redeposited coal clasts were probably originally deposited in coal swamps as were the Upper Silesian bituminous coals.

Investigation of pore structure and fractal characteristics of marine-continental transitional shales from Longtan Formation using MICP, gas adsorption, and NMR (Guizhou, China)

Abstract Organic-rich shale samples from marine-continental transitional facies of the Late Permian Longtan Formation in southwestern Guizhou were investigated using organic petrography analysis, X-ray diffraction analysis, mercury intrusion capillary pressure experiments, gas adsorption experiments, nuclear magnetic resonance, scanning electron microscopy image analysis, and multi-fractal theory to quantitatively and qualitatively investigate the full-size pore structure and fractal characteristics of the shale. The correlations among the total organic carbon (TOC) content, mineral composition, and pore structure were discussed. The fractal dimension was used to evaluate the production potential of a shale reservoir. Results show that samples have a high TOC content (4.38 wt % on average), low permeability (less than 0.001 mD), and complex pore structure. The pore volume (PV) varies from 0.001997 cm3/g to 0.03653 cm3/g, with an average of 0.02864 cm3/g, and the specific surface area (SSA) varies from 14.144 m2/g to 29.740 m2/g, with an average of 21.533 m2/g. Mesopores (diameter between 2 and 50 nm according to IUPAC) are the predominant contributors to the pore volume, while mesopores and micropores (diameter less than 2 nm) are the main contributors to the specific surface area. The shale samples with higher TOC and clay mineral content have larger PVs and SSAs and higher fractal dimensions than those that do not. A high fractal dimension indicates a rough pore surface and complicated pore structure. Shale with higher D1 and DA (representing the pore surface roughness and the adsorption space, respectively) has high adsorption capacity and favors gas accumulation, while shale with higher D2 and DS (representing the pore structure complexity and the seepage space, respectively) has greater flow capability and favors gas diffusion.

Comparative Study on Shale Characteristics of Different Sedimentary Microfacies of Late Permian Longtan Formation in Southwestern Guizhou, China

Organic-rich marine-continental transitional shales are widely distributed in Guizhou Province, China. Samples from the Late Permian Longtan Formation were investigated using organic petrography analysis, X-ray diffraction (XRD) analysis, field emission-scanning electron microscopy observations, mercury intrusion capillary pressure and gas adsorption experiments to better understand the organic geochemical characteristic, mineralogical composition, full-size pore structure characteristics and fractal characteristic of shale reservoir. The relationships among the total organic carbon (TOC) content, mineral composition, pore structure parameter, methane adsorption capacity and fractal dimension of shale samples are discussed, along with the differences between different sedimentary microfacies. Results show that shale samples are characterized by high TOC contents, low permeability, complex mineral composition and pore structure. Shales of YV-1, deposited in delta and lower delta plains, have an extreme high clay content (71.33% average) and the clay minerals mainly consist of the I/S and kaolinite, while shales of XD-1, deposited in the lagoon-tidal flat, have a relatively low clay content (37% average) and the I/S occupies an absolute advantage. The pore volume, specific surface area and average pore diameter of YV-1 (0.02881 cm3/g, 20.806 m2/g and 11.07 nm, respectively) are larger than that of XD-1 (0.02110 cm3/g, 20.101 m2/g, and 8.40 nm, respectively). The mesopore of YV-1 is the predominant contributor to the pore structure, while the micropore of XD-1 also occupies a certain proportion in addition to the mesopore. Organic matter (OM)-hosted pores are largely developed in XD-1 samples, while clay mineral-hosted pores dominate the pore system of YV-1. Shale samples with higher TOC content and clay content generally have larger specific surface area and pore volume, which provides more adsorption space and enhances pore structure heterogeneity. Samples of XD-1 have high TOC contents, suitable mineral composition and complex pore structure, suggesting that shales deposited in a lagoon-tidal flat environment may have a greater potential for shale gas development.

Maturity of dispersed organic matter in bituminous formations of the Ionian Zone (Epirus region, NW Greece)

The main objective of this paper is to study by means of Organic Petrology techniques, the maturity of the dispersed organic matter from certain sedimentary formations of the Ionian Zone, such as the Bituminous Shale, the Upper Siliceous Vigla Formation and the Bituminous Sandstone. The samples were collected from outcropping sites located in the region of Epirus. Initially they were treated with acids (HCl-HF) to remove most of the carbonate and silicate minerals. Then a ZnCl2 solution was used to concentrate the organic-rich fraction. Total Organic Carbon (TOC) content was determined applying dichromate oxidation. Polished blocks were prepared from the concentrated organic matter mounted in epoxy resin and examined under the coal-petrography microscope. Emphasis was given to maceral identification and vitrinite reflectance (R) measurements, which provide information regarding the quality and the maturity of the organic matter respectively, with implications for the petroleum generation potential regardless the level of alteration. The TOC and Rr values (4.74% and 0.68%, respectively) confirm to the oil potential of the Lower Jurassic Posidonia Shale. Nevertheless, it is suggested that detailed and higher resolution sampling focusing on the Lower Posidonia Shale, as well as organic petrography analyses coupled with Rock-Eval pyrolysis should be carried out in order to accurately determine its quality as petroleum source rocks.

Tracking Mid- to Late Holocene depositional environments by applying sedimentological, palaeontological and geochemical proxies, Amvrakikos coastal lagoon sediments, Western Greece, Mediterranean Sea

This study presents sedimentological, palaeontological, geochemical, mineralogical, and organic petrography data from a 30 m deep core representing a Mid- to Late Holocene lagoonal depositional environment, of a coastal area of Amvrakikos Gulf, Western Greece. Three horizons were dated using 14C. The sedimentological, palaeontological and geochemical interpretations of the lagoonal sediments reveal three major lithological units deposited between around 5200 and 1600 BP. The upper lithological unit extended to a depth of 11.20 m, the middle from 11.20 to 21.30 m, and the lower one from 21.30 to 30.00 m. A mean rate of sedimentation of 5.7 mm/y and a maximum rate of 12.6 mm/y were estimated. The mineralogical analysis and the magnetic susceptibility of the core points to a constant sediment – source supply. The Mid- to Late Holocene depositional environment mainly reflects inundation by the braid plain of the Arachthos and secondarily by the Louros River. The reconstruction of the depositional environments corresponds to a shallow marine and deltaic brackish lagoon and specifically to an environment proximal to river supply. The high rates of sedimentation, as well as the interpretation of depositional environments, indicate that the coastal sedimentological processes during the Mid- to Late Holocene were mainly controlled by the progradation of river deltas. Moreover, the geochemical proxies, the recovered molluscs and the microfauna, as well as the organic petrography analyses indicate periods of dysoxic and hypoxic conditions. These Holocene dysoxic and hypoxic events indicate that the recent dystrophic crises in the Amvrakikos Gulf are not only the result of human activities but also the contribution of natural processes.

Polycyclic aromatic hydrocarbons in effluents from wastewater treatment plants and receiving streams in Tianjin, China

Surface water, suspended particulate matter, pore water, and sediment samples were collected and analyzed for polycyclic aromatic hydrocarbons (PAHs) in Yongding New River, South Drainage Canal and North Drainage Canal, which receive most of wastewater from industrial city of Tianjin. PAH concentrations in effluent samples of wastewater treatment plants (WTP) discharging into the South Drainage Canal and North Drainage Canal were quantified for the first time. The results showed that the discharge of the WTPs recently only contributed to the PAH contamination in the canals near the outlets of the WTPs. PAH levels in sediments of the streams were greatly higher than those in soils by riverbank probably due to receiving large amounts of untreated wastewater. Unusually high benz[a] anthracene concentration strongly influenced the seasonal and spatial variation of total PAH concentrations in South Drainage Canal. Paired samples t test of ∑Nap, Fl, Phe, Fluo and ∑Nap, Phe, Fluo, Chry concentrations, which were dominant components in the air samples from non-heating and heating season, respectively, in the suspended particulate matters from the streams showed that PAH source from air deposition was more important for Yongding New River than that for South Drainage Canal and North Drainage Canal. Source apportionment based on PAH profiles indicated that coal combustion was the major PAH contamination source, and coke oven sources and wood combustion also contributed to the PAH contamination of the streams. This was further indicated by organic petrography analysis.