Hydrogen Index Research Articles

Organic petrology and geochemistry of the Devonian-Mississippian bakken formation, Williston Basin, North Dakota

The Devonian–Mississippian (D–M) black shales of the Bakken Formation are of interest as a hydrocarbon source due to their high total organic carbon (TOC; 2.2–17.4%) content. The Upper and Lower Members of the Bakken Fm. are shallow marine (100–150 m) sequences. Thirty samples were selected for maceral identification, kerogen typing, and solid bitumen reflectance (SBRo) based on TOC content and down-core spacing. The shales contain alginite, bituminite, abundant solid bitumen (SB), and minor amounts of inertinite. Solid bitumen increases in quantity with increasing thermal maturity. Pyrolysis (85 samples) provided S1 (avg. 8.0 mg HC/g rock), S2 (avg. 24.3 mg HC/g rock), hydrogen index (HI; avg. 201 mg HC/g TOC), oxygen index (OI; avg. 7 mg CO2/g TOC), and Ro (0.60–1.03%) calculated from Tmax. Plots of HI vs. OI and HI vs. Tmax (°C) were used to assess kerogen type but are not consistently in agreement with the petrographic assessment. Some samples from more thermally mature cores plot as Type III (vitrinite) kerogen instead of Type II (alginite and bituminite) kerogen, the latter confirmed through petrographic observations of lower maturation samples. This is largely due to increased SB in more thermally mature samples (Ro = 0.83–1.03%), as SB is known to have a lower HI content than Type II kerogen. Petrographic data show more alginite and bituminite (19–55%) in the thermally less mature samples (Ro = 0.60–0.83%) compared to more dispersed SB (67–86%) and less alginite and bituminite (<1%) in the more thermally mature samples (Ro = 0.89–1.01%).Early research on the Bakken Fm. reported lower than expected vitrinite reflectance values and attributed them to vitrinite “suppression”. The scarcity of vitrinite and abundance of SB suggest that early work likely reported reflectance on SB. Recent attempts to assess the thermal maturity of the Bakken black shales have converted SBRo to vitrinite reflectance equivalence (VRE). However, there are multiple SB populations present in these shales and it is not always clear which SB populations were included, possibly contributing to error. In the current study, only smooth, homogenous SB was measured (0.68–1.14% SBRo) and VRE values calculated (0.54–1.49%) to assess thermal maturity from the basin margin to the depocenter; inclusion of measurements on granular, heterogeneous SB (14–21 vol%), which are ~53% lower than those for smooth, homogenous SB (3–12 vol%), results in lower mean reflectances, especially in more mature samples. Vitrinite reflectance equivalent data calculated using the D–M New Albany Shale equation of Liu et al. (2019) agrees with liptinite fluorescence and Rock-Eval Ro, whereas VRE based on the D–M Woodford Shale equation of Cardott and Comer (2021) does not. This suggests the importance of applying VRE equations from similar formations both in terms of thermal history, as well as kerogen type and age. Results from SBRo, Rock-Eval Ro, VRE, and observations of alginite fluorescence indicate that samples from the current study range from the early oil window into the condensate, wet gas zone.

Paleoenvironmental Settings of the Soma Coal Basin (Turkey): Insights from Maceral Data, Biomarker, and Carbon Isotopic Composition.

Organic geochemical (TOC, pyrolysis, biomarker) and petrographic (maceral analysis) investigations together with organic carbon isotope studies were carried out to characterize in detail the depositional environment, determine the organic matter type, and assess the hydrocarbon production potential of three coal seams (KP1-upper, KM3-middle, and KM2-lower) in the Soma (Manisa, Western Anatolia) coal field in Turkey. The total organic carbon value of the upper coal seam ranged between 11.7 and 55.75%, the middle coal seam between 20.12 and 62.86%, and the lower coal seam between 50.03 and 65.71%. Coals in all three seams are characterized by low hydrogen index (HI) values (<151 mg HC/g TOC), low bitumen index (BI) (<19 g HC/g TOC), and quality index (QI) between 23 and 156 mg HC/g TOC. According to Rock-Eval pyrolysis data, the organic matter type of the coals is type III kerogen. Huminite reflectance, Tmax, and biomarker data (22S/22S+22R (C32) sterane, ββ/(αα + ββ) (C29) sterane, and MPI-1) indicate that the organic matter is not thermally mature and that the Soma-Manisa coal has reached the sub-bituminous rank. Rock-Eval data shows that coal is gas-prone and has not reached the maturity threshold required for initial gas production. The dominant maceral group is huminite while liptinite and inertinite macerals have been found in minor amounts. Groundwater index (GWI), vegetation index (VI), tissue preservation index (TPI), and gelification index (GI) parameters indicate a transition from limnic-limno-telmatic to limno-telmatic-telmatic environment from the upper seam to the lower seam. N-Alkane distributions show that paleoclimatic conditions have changed from KP1 to KM2. The higher abundance of pristane compared to phytane and low C35/C31-C35 homohopane index values demonstrate that the coals were deposited in a suboxic-oxic environment. The predominance of n-alkanes with generally high carbon number, relative variable abundances of C27-C28-C29 steranes, δ13C values, C/N ratios, and very low gammacerane index indicate a terrestrial ecosystem with nonmarine influence, although algae and microorganisms also contributed to the biomass.

An Improved Method for Evaluating Hydrocarbon Generation of Shale: A Case Study of the Lower Cretaceous Qingshankou Formation Shale in the Songliao Basin

AbstractBecause of the influence of hydrocarbons, especially adsorbed hydrocarbons, on the detection of cracked hydrocarbon (S2) and total organic carbon (TOC), the hydrogen index (HI)‐based hydrocarbon generation model deviates from actual practice. In this study, the shale in the first member of the Qingshankou Formation in the central depression of the Songliao Basin, where in northeastern China, was taken as the research object and a correction method for S2 and TOC was established. By correcting the experimental results of different maturity samples, the actual hydrocarbon generation model has been revealed, the differences before and after correction compared, and the evolutionary characteristics of the adsorbed hydrocarbon content were clarified. The results show that the organic matter enters the hydrocarbon generation threshold at Ro–0.5% and reaches the hydrocarbon generation peak at Ro–1.0% and that the hydrocarbon generation process ends at Ro–1.3%. The hydrocarbon generation model established based on the measured values has a ‘lag effect’ compared to actual values, and this extends the hydrocarbon generation window of organic matter and delays the hydrocarbon generation peak. With the increase of maturity, adsorbed hydrocarbon content shows the characteristics of ‘first increasing, then stabilizing, and then decreasing’, and reaches the most abundant stage at Ro of 0.9%–1.3%.

Geochemical evaluation of the carbonaceous shale associated with the Permian Mikambeni Formation of the Tuli Basin for potential gas generation, South Africa

Abstract The increasing demand for energy and global commitment to reduce CO2 emissions to mitigate climate change has spurred countries to pursue unconventional hydrocarbon generation for power production. The investigation of the carbonaceous shale from the Permian Mikambeni Formation of the Tuli Basin in South Africa aims to assess the potential for gas generation. The Rock-Eval 6 pyrolysis of the studied samples shows total organic carbon (TOC) content ranging from 10.10 to 37.61 wt%, indicating an excellent source rock quality since it exceeds the threshold limit of 5 wt%. The produced gas that emanated from the thermal breakup of remaining hydrocarbon (S2) ranged from 14.30 to 65.55 mg HC/g rock while the hydrogen index (HI) ranged from 56.55 to 198.22 mg/g TOC. The plot of the HI against T max indicates the predominance of type-III kerogen, prone to gas generation. The thermal maturity parameters, T max (430–466°C), and vitrinite reflectance, VRo (0.6–1.2), showed a matured organic material. The production index value (0.06) of the samples indicates a moderately mature source generating a biogenic gas. The carbon isotopic composition, δ 13C (−20.0 to −23.4‰), indicates a predominant influx of organic matter derived from a vascular higher plant. The studied samples showed relatively depleted values of oxygen isotopic composition δ 16O (14.1–18.8‰), suggesting a brackish water depositional environment. Additionally, the Ba concentration (303.15–331.27 ppm) exceeds the 200 ppm threshold for the marine environment, indicating a non-marine environment characterised by low marine paleo-productivity and high detrital influx. Based on the evaluation, the studied coaly-shale is found with a matured and type-III kerogen that is prone to gas generation in a fluvial, paleo-depositional environment.

Reproducibility of Rock-Eval® thermal analysis for soil organic matter characterization

Rock-Eval® (RE) is a thermal analysis technique increasingly used to characterise soil organic matter. To interpret the results, particularly when investigating differences between samples, it is necessary to know the expected ranges of analytical error associated with the RE measurements. Moreover, the RE analyzer is now at its seventh version (RE7) while most literature results were produced using the previous version (RE6). Thus, a characterization of the reproducibility of RE measurements is necessary. We measured the reproducibility of RE measurements using fifteen samples from French croplands and forests that were analysed on five different RE instruments, located in different laboratories and belonging to both generations RE6 and RE7. From each RE analysis, we extracted RE parameters commonly used for soil organic matter characterization and we performed the prediction of the active and stable soil organic carbon fractions using a machine learning model (PartySOC) that uses RE parameters. We obtained a measure of the expected relative errors in RE parameters and PartySOC predictions per instrument, across instruments of the same generation and across generations. We found that the parameters total organic carbon (TOC), mineral carbon (MinC) and R-index are well reproducible, even across the RE6 and RE7 generations. Instead, the hydrogen index (HI) and oxygen index (OI) are more sensitive to signal variations, even within the same generation, especially when TOC is low. The PartySOC predictions were well reproducible across RE6 instruments but not across RE generations. In the future, the results of this study will help discriminate relevant differences between soil samples characterised using RE thermal analysis.

Newly discovered Botryococcus-rich source rocks in the western Qaidam Basin, NW China and their implications for shale oil exploration in saline lacustrine basins

Owing to the high hydrocarbon content and photosynthetic efficiency of phytoplankton, planktonic microalgae account for the main source of petroleum hydrocarbons in marine and continental petroliferous basins. Therefore, the presence of algal residues in such basins is considered an important indicator of high-quality hydrocarbon source rocks. The southwestern region of the Qaidam Basin, characterized by lacustrine deposits from the Paleogene, has substantial petroleum resources. However, studies on the development of source rocks and the mechanisms involved in their organic matter enrichment are insufficient, thus hampering ongoing shale oil exploration efforts. Herein, abundant Botryococcus fossils were discovered in the main source rocks of the upper member of Xiaganchaigou Formation of Paleogene in Southwest Qaidam, accounting for >50 % of the total organic matter content. The palynofacies assemblages reflected relatively distal and oxygen-rich sedimentary environments. The algae-rich rocks usually exhibited distinctive laminated structures alternately composed of quartz-feldspathic, clay and carbonate laminae, indicating periodic climate fluctuations. The Botryococcus, which was mainly preserved in the coarse-grain quartz-feldspathic laminae, probably reflected heavy precipitation conditions and subsequently high nutrient inputs. Finally, the oxygen-rich, low salinity and eutrophic water was likely taking form which benefit the growth of these hydrobiontic algae. These algal-rich shales exhibited typically high hydrogen index (IH) and total organic carbon (TOC) values, indicating their high hydrocarbon-generation potential. Thus, they are important marker beds for high-quality source rocks in petroliferous basins. Concurrently, the coarse-grained detrital mineral laminae displayed excellent reservoir physical properties, probably providing sufficient reservoir space for planktonic algae-derived liquid hydrocarbon. Therefore, these Botryococcus-rich source rocks might represent important targets for ongoing shale oil exploration.

Generation and expulsion of Lower Jurassic hydrocarbon in different source rocks in the Taibei Sag, Turpan-Hami Basin, northwest China

Source rocks in the first (J1s1) and second (J1s2) members of the Lower Jurassic Sangonghe Formation (J1s) in the Taibei Sag, Turpan-Hami Basin, NW China, are shore-shallow lacustrine mudstone and semi-deep to deep lacustrine mudstone. These two sets of mudstones provide an excellent opportunity for investigating the origin and expulsion patterns of hydrocarbon from source rocks under different environments. Through systematic geochemical analysis, including total organic carbon (TOC), Rock-Eval analysis, GC-MS analysis, and major and trace element analysis, the geochemical characteristics and sedimentary environment of the Sangonghe Formation (J1s) source rocks were evaluated. By integrating kerogen kinetics modeling, a more precise assessment of the hydrocarbon generation and expulsion characteristics of the source rocks from both members of the Sangonghe Formation is achieved. The fine-grained sediments of the Sangonghe Formation were formed in a weakly oxidized brackish water body. The J1s1 mudstone was deposited in a shore-shallow lacustrine environment. The repeated river influx increased the input of terrestrial higher plants, which complicated the maceral composition and diluted the abundance of organic matter. The J1s2 source rocks were formed in the semi-deep to deep lacustrine environment during the maximum transgression period with a large thickness and high TOC values, the maceral composition was dominated by a mixed source of aquatic organisms and terrestrial plants. Consequently, the source rocks of J1s2 exhibit higher initial hydrogen index (HI0), hydrocarbon generation potential (Qg) and transformation ratio (Tr) compared to those of the J1s1 source rocks, while the interbedded mudstone with limited thickness in J1s1 exhibits a higher hydrocarbon expulsion efficiency (Re).

Multi-method characterization of the recent sediment from the Dibi subsidence lake in the tropical Adamawa region (central Cameroon): Implications for the palaeoenvironmental reconstruction

The evolution and functioning of various tropical ecosystems is poorly understood due to a lack of quantitative techniques to characterize the physicochemical composition of soils and sediment. Here, a detailed multi-method study of lithological changes is provided from a core taken from the silted-up Dibi subsidence lake (central Cameroon). To unravel the provenance of sediment, mineral constituents, and organic matter sources, an array of tools are applied including a spectrophotometer, a laser particle sizer, Rock-Eval pyrolysis, X-ray diffractometer (XRD), a portable X-ray fluorescence (XRF) spectrometry, and an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) instruments. The studied core consists of light-colored deposits at the base (Unit 1) overlain by dark humic deposits (Unit 2). The sediment is very well graded (grading index Sd < 0.35Ф), indicative of bottom suspended to rolling transport. Unit 1 is characterized by relatively low values of total organic carbon (TOC: 2%–5%) whereas the dark Unit 2 has high contents of TOC (10%–33%). The core shows a high oxygen index (OI) value (average = 207 mg carbon dioxide (CO2)/g TOC) and a low hydrogen index (HI) value (average = 107 mg hydrocarbon (HC)/g TOC). This indicates highly altered organic matter (OM), likely from decomposed terrestrial plants. The chlorophyll-α fingerprint (peak around 675 nm) also reveals an autochtonous primary production of organic matter. The mineralogical assemblage of Unit 2 comprises kaolinite, quartz, feldspars, montmorillonite, ilmenite, siderite, gibbsite, rutile, and anatase whereas that of Unit 1 is similar but differs with the presence of illite and the absence of gibbsite. The high titanium dioxide (TiO2) and zirconium (Zr) contents confirm that the source rocks also are comprised of granites, and gneiss without volcanic rocks, such as basalts and trachytes. The source rocks have been intensively weathered using some parameters such as ln(Al2O3/Na2O), K2O/Rb, K/Al, and weathering indices, where Al2O3 denotes aluminum oxide, Na2O denotes sodium oxide, K2O denotes potassium oxide, Rb denotes rubidium, K denotes potassium, and Al denotes aluminum. The enrichment factors (EF) of redox-sensitive trace elements and their relation with TOC, the negative values of manganese/iron ratio (Mn∗) associated to three elemental ratios (cupper/zinc (Cu/Zn), thorium/uranium (Th/U), and vanadium/chromium (V/Cr)) attest to the predominance of sub-oxic to anoxic bottom waters in Dibi lake during sediment deposition. The data also show low primary productivity at the base of the core, followed by an increase towards the top, linked to the intensification of weathering and facilitated by humid climatic conditions, usually increase terrestrial input and palaeoproductivity. The petrological data show a generally warm and humid palaeoclimate. This climatic variation has contributed to the large spread of the savannah and disappearance of the forest. This study sheds light on the late Pleistocene to Holocene palaeoenvironment evolution of the Adamawa region which could be integrated into the context of the Pleistocene to Present regional evolution of the tropical palaeoenvironment.

Petrographic and geochemical analysis of Barmer Basin Paleogene lignite deposits: Insights into depositional environment and paleo-climate

The current study attempts to characterize the samples from Kapurdi, Giral and Sonari lignite mines of Barmer Basin within Rajasthan Tertiary Lignite deposits using petrographic and geochemical techniques. The data generated has been studied in order to better understand the geochemical properties, hydrocarbon potential, depositional environment and paleo-climatic condition of the paleo-mires of these lignites. The proximate analysis of the samples reveals that the average ash content of the Barmer Basin is 11.93 %, the average moisture content is 14.08 %, average volatile matter yield is 42.03 % and the average fixed carbon is 31.95 %, which suggesting that the physical properties of lignite are dominated by volatile matter on dry basis. The ultimate investigation reveals the chemical properties of the lignite with the average carbon content found to be 58.79 wt%, hydrogen value 3.83 wt%, nitrogen percentage 1.60 wt% and sulphur content 2.75 wt%. This clearly indicates high sulphur concentration in Barmer lignite deposits, based on dry basis. The lignite samples subjected to FTIR studies identified aliphatic CH group, aromatic CO group, hydroxyl OH and Aldehyde HCO group. The Rock-Eval pyrolysis studies have been carried out to know the coalification profile of the deposits and hydrocarbon source rock potential. The varying behaviour between brown coal lithotype are primarily reflected by changes in oxygen index values, whereas hydrogen index values demonstrate a more pronounced correlation with coal type rather than the level of maturation. The results show the average total organic carbon (TOC) 47.29 %, S1 peak 2.18 mg HC/g, S2 peak 88.70 mg HC/g, S3 peak 19.22 % mg CO2/g, Tmax 410.53 °C, hydrogen index 219.2 mg HC/g TOC and oxygen index 46.33 mg CO2/g TOC. According to petrographic investigations, the huminite macerals dominate followed by liptinite and inertinite maceral groups in mineral matter-free basis. In all the three different lignite mines, the huminite group dominates with preserved sub-maceral ulminite indicating less transformation of structured plant matter. Reconstruction of depositional environment and paleo-climatic condition of the paleo-mires has been attempted by using organic petrographic indices. The high gelification index (GI) and low tissue preservation index (TPI) values suggest a prolonged wet environment during the decomposition of organic material, accompanied by a gradual subsidence process. The ground water influence index (GWI) and vegetation index (VI) denote ombrotrophic to mesotrophic hydrological conditions of basin at the time of deposition.

Petroleum system of the fold-and-thrust belt of the United Arab Emirates: New insights based on 1D and 2D basin modeling

The hydrocarbon potential of the fold-and-thrust belt (FTB) in the United Arab Emirates (UAE)-Oman mountains has received limited attention to date, leading to a poor understanding of the petroleum systems in this region. Despite the existence of hydrocarbon fields within the FTB, the source rock potential has not been adequately studied. This study aims to address this knowledge gap using 1D and 2D basin modeling approaches to evaluate the petroleum system of the FTB. In addition, gas chromatographs are also used to correlate hydrocarbon occurrences with their source rock. This study's findings identify the Silurian, Upper Cretaceous, Paleocene–Eocene, and Oligocene formations as the primary source rocks in the study area. Silurian shales, encountered in a well in the northern UAE, are currently considered overmature. The Cenozoic source rocks exhibit a spectrum of Total Organic Carbon (TOC) content, ranging from less than 1 to as high as 2 wt%, leading to variable degrees of expulsion efficiency. The maturity of these rocks varies based on their position in relation to the FTB and foredeep, with increasing maturity towards the north. The Upper Cretaceous sequences display low TOC and Hydrogen Index, indicating very low expulsion efficiency. The present-day distribution of maturity is largely influenced by Late Cretaceous and Oligocene–Miocene compressional events that affected the northern and northeastern Arabian Plate. This analysis shows that hydrocarbon expulsion from the Silurian source rocks was initiated during the Middle-Late Jurassic. These hydrocarbons are presumed to have migrated through Upper Permian, Jurassic, and Lower and middle Cretaceous reservoirs. Westward hydrocarbon migration, towards a regional bulge, may have also occurred following compressional events that resulted in lithospheric flexure and formation of the foreland basin. Notably, certain exceptions to migration towards the bulge include structural entrapment of hydrocarbons beneath the main frontal thrust zone of FTB and some structural traps beneath the Lower Fiqa Formation.

An R V Map of the Milky Way Revealed by LAMOST

The total-to-selective extinction ratio, R V, is a key parameter for tracing the properties of interstellar dust, as it directly determines the variation of the extinction curve with wavelength. By utilizing accurate color excess measurements from the optical to the mid-infrared range, we have derived R V values for approximately three million stars from LAMOST data release 7 using a forward-modeling technique. This extensive data set enables us to construct a comprehensive 2D R V map of the Milky Way within the LAMOST footprint at a spatial resolution of ∼27.′5. Based on reliable sight lines of E(B − V) > 0.1, we find that R V exhibits a Gaussian distribution centered around 3.25 with a standard deviation of 0.25. The spatial variability of R V in the Galactic disk exhibits a wide range, spanning from small scales within individual molecular clouds to large scales up to kiloparsecs. A striking correlation is observed between the distribution of R V and molecular clouds. Notably, we observe lower R V values within the regions of nearby molecular clouds compared to their surrounding areas. Furthermore, we have investigated the relationships between R V and various parameters, including dust temperature, dust emissivity spectral index, column densities and ratios of atomic and molecular hydrogen, as well as the gas-to-dust ratio. We find that these relationships vary with the level of extinction. These analyses provide new insights into the properties and evolution of dust grains in diverse interstellar environments and also hold significant importance for achieving accurate extinction corrections.

Using 1H low-field NMR relaxometry to detect the amounts of Robusta and Arabica varieties in coffee blends

Low-field nuclear magnetic resonance (LF-NMR) is a method of widespread use in food research due to its non-destructive character and the relatively low cost of the instruments, allowing the determination of oil / fat contents and the achievement of images of different types of food materials, among other uses. In this work, 1H LF-NMR relaxometry was used to distinguish the contributions due to Arabica and Robusta coffee varieties present in coffee blends. As the method detects preferentially the NMR signals due to phases with high molecular mobility, which exhibit longer values of the 1H transverse relaxation time (T2), the difference in the oil contents associated with Arabica and Robusta coffee was the key factor responsible for the detection of the contributions due to each variety. The analysis presented in this work showed that the relative hydrogen index is a useful parameter to be used in quantitative analyses of the contents of each coffee variety present in the blends. The results illustrate the high potential of applicability of LF-NMR relaxometry as a screening tool for quality control and adulteration detection of coffee-related products.

Impact of Thermal Maturation of the Upper Cretaceous Bituminous Limestone of Attarat Um Ghudran Central Jordan on Calcareous Nannofossil Preservation.

Oil shale deposits of the Late Cretaceous from three boreholes in central Jordan were examined to assess the impact of thermal maturation on the content of nannofossils. Thermal activity has been shown to have a strong effect on organic matter content and composition but its effect on calcareous nannofossil assemblages remains inconclusive. This study aims to determine the impact of thermal maturation on nannofossil assemblages and to compare this to an estimated maturity level based on bulk geochemical analysis. Micropaleontological and geochemical analyses were conducted on 31 samples from three oil shale wells drilled in Attarat Um Ghudran central Jordan. Several types of nannofossil preservation have been recorded, including dissolution, overgrowth, and breakage. In the Jordan oil shale sections, nannofossils exhibit a variety of preservation types, with intense dissolution in the middle part of the study sections. The vast majority of the samples had high TOC enrichment, with 29 samples exceeding values of >10%. Kerogen recovery and quality from the oil shale are very good, with a predominance of fluorescent amorphous organic matter (AOM) and minor algal components. The low fluorescence preservation index (FPI), which is 1 in most of the samples, indicates that alteration occurred due to intense thermal activities in the study interval. The palynomorph and AOM fluorescence, ranging from a spore coloration index (SCI) of 3 to 5, suggest that the studied samples were approaching the oil window. A correlation between the nannofossil preservation and geochemical parameters shows a predominance of poorly preserved nannofossils along with high total organic carbon contents and an elevated hydrogen index (HI). We show that low FPI values and a higher level of maturity are associated with poor nannofossil preservation, suggesting that nannofossils, in conjunction with petrographic analysis of kerogen, could be used as a rapid screening technique for estimating levels of oil-shale maturity. The nature of the tectonism in the study area, including faulting and a metamorphosed zone, enhanced the maturity, which might explain why the nannofossils were so significantly affected.

Thermal maturity calculation in Type II-S source rocks using the alkyl dibenzothiophenes

Distributions of the alkyl dibenzothiophenes (DBT) are proven as effective proxies for the thermal maturity of bitumen extracts and oils expelled from marine source rocks containing Type II-S kerogen. Here we report on an expanded sample suite and DBT ratios to further refine these relationships. This study investigates the methyldibenzothiophenes (MDBT), dimethyldibenzothiophenes (DMDBT), and trimethyldibenzothiophenes (TMDBT) in 52 source rocks from formations in the United States and the Middle East to substantiate the reliability of these sulfur-bearing compounds to estimate maturity in Type II-S samples. The isomerization of MDBTs, DMDBTs, and TMDBTs shows strong correlations with pyrolysis data (Tmax, hydrogen index, and equivalent %VRo), enabling a direct calculation of thermal maturity from the ratios of the MDBT homologous series. Maturity indicators from biomarkers and other ancillary compounds are also analyzed to highlight the limitations and inconsistencies that can be observed when applying such methods to assess the maturity of Type II-S samples. The derived MDBT, DMDBT, and TMDBT maturity equations provide a reliable assessment of maturity for Type II-S samples, ranging from the immature window to the end of the condensate/wet gas window. Moreover, evaluation of 18 sulfur-rich oils validates the application of MDR maturity equations to fluid samples. Such flexibility allows for inclusive, yet consistent, maturity assessment in sulfur-rich formations when compared to other molecular maturity proxies.

Microfossils, High-Resolution Stratigraphy, Geochemistry and Lithology of the Upper Jurassic and Lower Cretaceous (Urdyuk-Khaya and Paksa Formations) in the Nordvik Peninsula, Anabar Bay, Laptev Sea

Abstract —The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic–Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

Time-Lapse Pulsed-Neutron Logs for Carbon Capture and Sequestration: Practical Learnings and Key Insights

Pulsed-neutron logs are a staple of time-lapse monitoring programs for saline aquifer carbon capture and sequestration (CCS) projects and are unsurprisingly the most frequently run wireline logs in both injection and monitoring wells. While the emphasis imposed by government regulators and the focus of operators to date has been on the verification of CO2 containment, it is envisioned that a savvy interpretation of the multiple independent measurements should be able to unlock much greater value for the project than merely detecting the location of stored CO2. Recently introduced capabilities for novel measurements and improved environmental compensation should further increase the repeatability, interpretability, and value of these logs. We reviewed more than 30 time-lapse runs of pulsed-neutron logs acquired over a period of 15 years on three mature CCS projects using both previous- and new-generation pulsed-neutron tools, including measurements of formation sigma, hydrogen index, and fast neutron cross section. Special attention in processing is required when changes occur to the wellbore environment between runs, although this is mitigated by the improved environmental compensation scheme of the newer tool. We performed both standalone estimates of CO2 saturation from single-physics time-lapse measurements and simultaneous interpretation of multiple independent time-lapse measurements and studied the results side-by-side with openhole log interpretation, core analysis, and well test results from the evaluation phase. The apparent changes in saturation were framed within the context of the injection history and important events in the life of the wells. A first finding is that differences in apparent CO2 saturation between the various independent measurement physics of the pulsed-neutron tool are often reconcilable and may carry additional information about the state of the well or reservoir. With respect to verification of containment, depending on the well configuration, it may be possible to differentiate between CO2 in the formation and CO2 in the annulus. The interpreted CO2 saturation itself can have different significance depending on the timing of acquisition and the type of well. Measured at the right time, it is a direct in-situ measurement of formation CO2 storage efficiency. In other cases, the interpretation reveals formation dryout in the near-wellbore region of injection wells, a condition that may presage loss of injectivity. We now understand that it is important for operators to plan the timing and frequency of pulsed-neutron runs according to what they want to measure and not based solely on regulatory obligations. In a CCS project, time-lapse pulsed-neutron logs should be thought of as much more than simple indicators of the presence and migration of CO2. They give important information about migration pathways. They can also help to quantify essential uncertainties on reservoir performance that are difficult to ascertain during evaluation. For example, storage efficiency is difficult to quantify with openhole logs since the formation is initially at zero CO2 saturation. Yet it is one of the keys to determining the ultimate storage capacity of any reservoir. Time-lapse pulsed-neutron logs provide an abundance of information that, when properly history matched, can greatly improve our models of CCS reservoirs to better navigate both the economic and operational risks associated with these projects.

Influence of runoff regulation on hydrochemical indicators of water in small rivers on the example of the Teplaya river in the Saratov region

Small rivers are extremely sensitive to any anthropogenic activity, including runoff regulation, and serve as a kind of indicator of the ecological state of natural complexes. In general, large rivers are well studied, and small water bodies are practically not studied, although they are of great economic importance. For Teplaya river of the Saratov region was given an ecological and geographical characteristic, sources of anthropogenic load on the reservoir were identified, an analysis was made of the degree of knowledge and background indicators of the rivers of this basin. On the example of Teplaya river effect of runoff regulation of a small river by a dam on a number of physical and chemical parameters of pond water quality is considered. It has been established that the water temperature in the Teplaya river in the autumn period before the runoff regulation was a constant value, and after the dam it increased to the last sampling point downstream. The hydrogen index varied within 7.5-8.4, the total mineralization of water consistently increased in the studied section of the river (0.66-1.08 g/dm3). It is shown that the content of ammonium ions and nitrites was much higher than the sanitary and hygienic standards, which indicates the uniform nature of fresh organic water pollution in this section of the river. An increase in the concentration of chlorides in the last of the cascade of ponds was established - almost 1.5 times compared to the higher sampling points, which, however, did not exceed the standard values.

Оценка экологического состояния реки Сояна в зоне возможного воздействия алмазоносного месторождения

The article presents the results of a comprehensive study of the Soyana River for the first time. The characteristics of hydrological and hydrochemical parameters were obtained while observations in July 2020 and March 2021. Changes in the hydrogen index (pH), mineralization, and the content of dissolved oxygen and biogenic elements in water, as well as petroleum hydrocarbons in water and bottom sediments were studied using generally accepted in hydrochemical practice methods. The data obtained were evaluated for compliance with the regulatory requirements for the river water quality. According to the chemical composition, the Soyana River water belongs to the hydrocarbonate class of small and medium mineralization (164–296 mg/L), weakly acidic and slightly alkaline type (pH 6.0–8.2). The data obtained allow us to conclude that there is no noticeable anthropogenic impact on the considered watercourse. The petroleum hydrocarbons content in water and bottom sediments was below maximum permissible concentrations. In river water it was below 0.010 mg/L, in bottom sediments – in the range from 0.2 to 3.2 mg/kg. The maximum content of petroleum hydrocarbons in soils was recorded in the lower course of the river, where bottom sediments are presented in the form of silty sand. The interannual variability of hydrological and hydrochemical characteristics in the direction from the source to the mouth of the river is estimated. The relationship and regularity of their distribution was specified. The data obtained can serve as background data for assessing the negative impact in case of anthropogenic load on the river basin.

Geochemical Evaluation of the Lower Senonian Ogugu Shale, Southern Benue Trough, Nigeria: Implication for Source Richness, Quality and Petroleum Potential

The Lower Senonian Ogugu Shale is the topmost layer of the Coniancian-Santonian depositional unit in the Southern Benue Trough. Sediments of this unit have been suggested to have huge potential for hydrocarbon generation. However, detailed geochemical studies on the organic matter source, thermal maturity and the hydrocarbon potential Ogugu Shale are still missing. For the present study, a total of 16 cuttings and 3 core samples of the Ogugu Shale from Amasiodo-1 well were subjected to total organic carbon (TOC), Rock-Eval pyrolysis and gas chromatography mass spectrometry (GC-MS) analyses in order to characterize the organic matter richness, kerogen type and liquid hydrocarbon-generative potential in the samples. The TOC values (0.70 to 1.20 wt. %) and Rock-Eval pyrolysis data S2 (0.26-0.73 mg HC/g rock) as well as its calculated parameters Hydrogen Index (HI; 23-72 mg HC/g rock) and Generative Potential (GP; 0.33-0.84 mg HC/g rock) suggest poor to fair organic rich rock containing dominantly terrestrially derived Type III kerogen. The biomarkers as well as the source-indicating aromatic hydrocarbons in the samples suggest contributions from mixed aquatic and vascular organic matter deposited under oxic-dyoxic conditions of deltaic paleoenvironment. The Rock-Eval pyrolysis Tmax (434-4560 C) including the derived vitrinite reflectance (Rc; 0.65-1.05%) indicate thermally matured source rocks. The thermal maturity status of Ogugu Shale is further supported by molecular thermal parameters from the saturate and aromatic compounds. This study therefore conclude that that the Senonian Ogugu Shale of the Southern Benue Trough contain thermally matured fair quantity of organic matter with poor hydrocarbon potential.

Source-rock evaluation of the Triassic – Jurassic interval of the Tanga Basin, coastal Tanzania

The Triassic-Jurassic interval is known to be the main source of oil and gas generation across the world. In the Tanga Basin of Tanzania, however, the potentiality of these strata for oil and gas generation has remained poorly understood. This study presents the organic geochemical analysis of the source rock within the Triassic-Jurassic interval of the Tanga Basin, integrating rock-eval pyrolysis, vitrinite reflectance and spore coloration analyses to assess the organic richness, quality and maturity for hydrocarbon generation. The results reveal that the Triassic and Jurassic shales are organically rich, with average total organic carbon (TOC) values of 1 wt % and 2 wt %, respectively. Triassic shales demonstrate the dominance of kerogen types II (oil), III (gas pone), II/III (gas with minor oil), and IV (inert) as indicated by hydrogen index values between 365 and 15 mg HC/g TOC. The hydrogen index (HI) values in the Jurassic interval range from 87 to 162 mg/HC/TOC, suggesting the dominance of kerogen type III (gas prone). Pyrolysis Tmax, vitrinite reflectance (Ro) and spore color index (SCI) indicate that the Triassic interval is thermally mature into a gas generation window, with average Tmax values of 450 °C, Ro ∼ 1.7% and SCI ∼8.5. The Jurassic interval is also revealed as thermally mature, with average values of Tmax ∼ 452 °C, Ro ∼ 0.7% and SCI ∼ 7.2, indicative of oil window. The positive findings of this study lay out an important foundation to follow up studies and extended exploration for hydrocarbon accumulations in the poorly explored Tanga Basin and across the coastal Tanzania in general.