Total Organic Carbon Values Research Articles

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.

Chemical and Mineralogical Characterisation of Clayey Sands from the Ivorian Serimentaru Basin in Road Construction

In Ivory Coast, particularly in the south, most paved and unpaved roads are made of clayey sand, given its availability. The early degradation of roads is related to a strong sensitivity of certain materials to the environment (climate, geology, and degrees of alteration) and a poor knowledge of the geotechnical properties could slow down their use in road construction. Within this framework, this paper focuses on determining the chemico-mineralogical nature of the clayey sands of the localities of Bingerville and Samo, in the South-East of Ivory Coast. Tests were conducted based on the chemical and mineralogical analyses. Chemical elements were determined by atomic absorption spectrometry, colorimetry, complexometry, and gravimetry. Organic matter was determined using the Rock-Eval 6 pyrolysis method, while the mineralogical composition was determined using a Bruker D8 ADVANCE diffractometer. The chemico-mineralogical analyses reveal that the clayey sands from Bingerville and Samo are more enriched in silica oxide (SiO2) but less enriched in iron oxide (Fe2O3). All the soils studied have a degree of laterization greater than 2, which suggests that they are non-lateritic soils. The low Total Organic Carbon (TOC) values lies between 0.1 and 0.15% by weight, which reflects the extremely low amount of organic matter in these soils. This indicates the possibility of treating these soils with hydraulic binders. The mineralogy of the studied soils denotes that they are composed of kaolinite and illite.

Nano-Scale Pore Structure Characterization and Its Controlling Factors in Wufeng and Longmaxi Shale in the Zigong Area, Southwest Sichuan Basin

The nano-scale pore systems in shale reservoirs control shale gas transportation and aggregation, which is of great significance for the resource evaluation of shale oil and gas and the selection of a “sweet spot”. Taking twelve marine shale samples from the Wufeng–Longmaxi Formation in the Zigong area, southwest Sichuan Basin, as the research target, we carried out a series of experiments, including total organic carbon (TOC) analysis, X-ray diffraction (XRD), gas adsorption (CO2 + N2), and mercury intrusion porosimetry (MIP), to study the full-scale pore structure characterization and controlling factors of pore volume and specific surface area. The results presented the following findings. (1) Marine shale samples from the target area are rich in organic matter, with an average TOC value of 3.86%; additionally, the mineral composition was dominated by quartz and clay minerals, with average contents of 44.1% and 31.4%, respectively. (2) The full-scale pore size distribution curves of pore volume developed multimodally, with the main peaks at 0.5 nm–2 nm, 3 nm–6 nm, and 700 nm–2.2 um; moreover, the full-scale pore size distribution curves of a specific surface area developed unimodally, with the main peak ranging from 0.5 nm to 1.2 nm. (3) Pore volume was mainly contributed by mesopores and macropores, with an average contribution of 46.66% and 42.42%, respectively, while the contribution of micropores was only 10.91%. The specific surface area was mainly contributed by micropores and mesopores, with an average contribution of 64.63% and 29.22%, respectively, whereas the contribution of micropores was only 6.15%. (4) The TOC content mainly controlled the pore volume and specific surface area of micropores and mesopores, while the clay and feldspar content generally controlled the pore volume and specific surface area of macropores. Additionally, the quartz content had an inhibitory effect on the development of all pore types. These results will help researchers understand the laws of gas accumulation and migration.

A 1000-year record of paleoclimate and paleoenvironment change inferred from sedimentary organic matter in Lake Azuei, Haiti

We studied sediment organic matter (OM) to reconstruct the environment over the last millennium using a sediment core from Lake Azuei, Haiti, also known as “Etang Saumatre.” Chronology for the 84-cm-long core was established with 11 14C dates and 210Pb analysis. Total organic carbon (TOC) concentrations in the sediment were low (0.58 ‐ 4.89%), as were total nitrogen (TN) values (0.06 ‐ 0.40%). Carbon isotopic ratio (δ13C) values were relatively negative and C/N ratios were low, suggesting that algae and terrestrial C3 plants were the primary sources of OM in the lake sediment. The inverse relationship between the nitrogen isotopic ratio (δ15N) and TOC is related to denitrification in the sediment. We identified five stratigraphic zones using a δ13C vs. C/N cross diagram: 1) Medieval Climate Anomaly 1 (MCA1) (1000–1050 CE), 2) Medieval Climate Anomaly 2 (MCA2) (1050–1100 CE), 3) Transition period between Medieval Climate Anomaly and Little Ice Age (MCA-LIA) (1150–1400 CE) 4) Little Ice Age (LIA) (1400–1800 CE), 5) Current Warm Period (CWP) (1800–2000 CE). These stratigraphic zones correspond to three climate episodes. The first was applied MCA1 and LIA periods, when there was a decrease in TOC and TN as well as in plankton-derived OM. This was accompanied by an increase in δ15N, which suggests denitrification due to suboxic conditions, likely caused by an increase in lake water temperature and dry conditions. The second climate episode was the MCA-LIA transition period and was characterized by high variability of TOC, δ13C and δ15N. The organic matter deposited during this period appeared to be a mixture of material originating from both autochthonous phytoplankton and allochthonous C3 plants. There was climate instability during this period, with alternations between wet and dry conditions, and thus likely variations in lake level. The third climate episode, the MCA2 and CWP periods, was characterized by an increase in TOC and TN values, and decrease in δ13C and δ15N values. This was chiefly attributable to more organic material input which was derived from C3 terrestrial vegetation growing around the lake. A decrease in δ15N indicated a reduction in denitrification, further suggesting an increase in the input of organic matter. Sedimentation during these periods occurred when there was more transport related to wet conditions.

Utilization of Digestate from Agricultural and Food Waste for the Production of Biochar Used to Remove Methylene Blue

The treatment of waste or by-products from the agri-food industry in agricultural biogas plants results in the production of biogas. After anaerobic digestion, digestate remains and is often used for soil fertilization. The solid digestate (SD) can also be used for the production of biochar, a material with specific properties and many applications. Such a model of operation fits perfectly into the concept of a circular economy, because the waste material can be used to produce an adsorbent that can be used to treat industrial wastewater. The research assumption of this study was to investigate selected properties of biochar prepared at variable temperatures in the pyrolysis process from solid. The potential of biochar for methylene blue (MB) sorption was also initially investigated in terms of biochar’s suitability for immobilizing metals in degraded soils. Biochar was produced at temperatures between 400–900 °C, with a temperature gradient of 50 °C. The efficiency of the production was in the range of 51–40% and decreased with the increasing temperature. The rising process temperature was also accompanied by a decrease in the nitrogen and hydrogen content of biochar. The produced biochar had an alkaline pH ranging from 11.40 to 12.69 and it increased as the temperature increased. The rise in the pyrolysis temperature effected a significant increase in the specific surface area BET (Brunauer–Emmett–Teller) in the case of biochar BSD750, BSD800, and BSD850 (BSD—biochar solid digestate). When analyzing the C content of individual biochar variants, there was no clear downward or upward trend, just as in the case of TOC (total organic carbon) value for the produced biochar. The greatest potential for removing MB (methylene blue) from solutions was demonstrated by biochar produced at 650–900 °C. The ability to remove MB rose along with the production temperature of the biochar.

Variable depositional environments and organic matter enrichment of Early Cambrian shales in the Middle Yangtze region, South China

Organic-rich shales of the Lower Cambrian Shuijingtuo Formation (SJT) in the Middle Yangtze region (South China) represent an important target for shale gas exploration and development in China. The lower section of the SJT mainly consisting of organic-rich black shale deposits has been regarded to be a favorable target for shale gas exploration and received substantial attentions, while the upper section of the SJT primarily consisting of limestone, silty shale and black shale deposits has been rarely studied. Most recently, a major breakthrough of shale gas exploration and development has been made in the upper section shale deposits. In order to better understand the redox evolution of sedimentary environment throughout the whole Early Cambrian time and organic matter (OM) enrichment mechanism of the SJT shale deposits, geochemical investigations, including analyses of total organic carbon (TOC), as well as major and trace element compositions, were conducted on the upper section of the SJT shales from Well EYY1. Our results showed that the upper section of the SJT shale deposits was accumulated during the Cambrian Stage 3. The TOC values of the studied SJT shale samples ranged from 0.34 to 3.65 wt%. The lower part of the upper section of the SJT shale, which exhibited relatively high TOC contents (∼2.0 wt%), was deposited under anoxic bottom-water conditions during the early Cambrian Stage 3, while the upper part, showing relatively low TOC content (1.0 wt%), was deposited under suboxic bottom-water conditions with intermittent episodes of anoxic bottom-water conditions during the middle–late Cambrian Stage 3. The palaeo-productivity of the SJT shale was estimated to be generally low, and displayed little variation. The OM enrichment mechanism of the SJT shale deposits underwent dynamic changes due to relative sea-level changes in the Yangtze Ocean. The OM enrichment of the early and late Cambrian Stage 3 shale deposits was primarily controlled by reducing conditions, while that of the middle Cambrian Stage 3 shale deposits may have been influenced by episodic upwelling activities.

Improving properties of bilge water’s treatment sludge in a port reception facility by novel continuous ultrasonic reactor

ABSTRACT The main problem faced by facilities dealing with bilge water treatment is the generation of a high sludge amount, which has significant contents of oil and hazardous substances. The presence of petroleum and petroleum-derived organic oil, which ranges from 10 to 20% in bilge water with varying characteristics not only poses challenges in treating the bilge water but also complicates the management of the bilge water treatment sludge. Hence, this study aims to improve the characteristics of treatment sludge generated after bilge water treatment at one of Turkey’s largest port waste reception facilities (PRF), consisting of a combined process involving ultrasound and a filter press. When the filter press was used to reduce the water content in the sludge cake to approximately 65%, a similar water content of about 65% was achieved by employing ultrasound as a pre-treatment, even when the initial sludge contained 95–98% water. Additionally, the application of ultrasound before the filter press did not have a significant impact on the values of total organic carbon (TOC) and loss on ignition (LOI). However, the value of dissolved organic carbon (DOC) decreased by 45% when subjected to sonication for 60 minutes at a density of 100 W/L. Furthermore, when ultrasound was applied as a pre-treatment, an increase in the sonication duration resulted in improvements of 10% and 22% in the parameters of total dissolved solids (TDS) and chloride, respectively, which were influenced by different levels of ultrasonic power. Briefly, such research has been novelly conducted on the management of bilge water treatment sludge. Ultrasound, which is often preferred in sludge dewatering applications, was applied to this type of sludge for the first time, and the studies were conducted in a pilot-scale facility and a real PRF field. In conclusion, the partially promising results of this study will provide a new alternative and a pioneering guide for the treatment of bilge water sludge.

Study of Hydrocarbon Potentials and Sedimentary Properties of Ispartaçay Formation, Turkey

The idea of the current work was the combination of the organic geochemical analyses, and the study of sedimentology characteristics of the source rock samples collected from the Ispartaçay Formation (Cretaceous period) between the city of Antalya and the city of Isparta, southwestern Turkey. Total Organic Carbon analysis and Rock-Eval pyrolysis were performed on the 24 samples taken from the study area, in order to evaluate quantitatively, and qualitatively organic matter and thermal maturity to determine the potential for hydrocarbon production. As well as studying the petrographic features (component and diagenesis), microfacies analysis, and sedimentary environment of the Ispartaçay Formation. The successions of the Ispartaçay Formation are poor to fair organic matter content and consist of dark grayish limestone, marly limestone, shale, massive cherty limestone, and thin-bedded radiolarian limestone. Total Organic Carbon values indicate that Ispartaçay Formation rocks are fair potential. Besides this, most of the samples from the Ispartaçay Formation contain mature to pot-mature (Type III -Type IV) kerogen. Petrographically, the particle portion of the Ispartaçay sediments is composed mainly of radiolarians, and planktonic foraminifera, In addition to the presence of a proportion of benthic foraminifera, whereas the groundmass is composed of micrite. Generally, the present sediments are subjected to some diagenetic processes like silicification, cementation, and dissolution. The microfacies analysis revealed that the succession of the Ispartaçay Formation is composed of alternations of two major microfacies, namely lime mudstone and lime wackestone microfacies. Depending on the facies and petrographic evidence, Ispartaçay Formation represents sediments deposited in the mid to outer ramp environment.

Seasonal Monitoring of Water Quality Parameters and Pesticides at the Altınapa Reservoir Watershed

Altınapa Reservoir is a reservoir located on the Meram Stream in the Konya Province in Türkiye that supplies drinking water. The Altınapa Reservoir feeds the Konya Drinking Water Treatment Plant with 37.8 million m3 of water annually and the treated water is delivered by the drinking water network. The aim of this study was to determine the effect of agricultural activities and settlements on water quality in the Altınapa Reservoir Watershed. In the study, major water quality parameters (pH, electrical conductivity, total organic carbon, total nitrogen, nitrite, nitrate, phosphorus, phosphate, and total suspended solids) and pesticides were monitored at four stations (K1, K2, K3, K4) on the sub-streams feeding reservoir. Major water quality parameters were monitored at monthly intervals for 12 months between June 2020 and May 2021, and pesticides were monitored seasonally at 4 seasons (Fall 2019, Winter 2020, Summer 2020, and Spring 2021). A correlation matrix was used to assess the connections between nine indicators of water quality. The annual average conductivity and pH values of the samples taken from four different stations of the Meram Stream were 432 µS/cm and 8.04, respectively. The highest value for total nitrogen was 10.73 mg/L and it was 0.87 mg/L for nitrate. Annual average total organic carbon values were determined as 1.35, 1.69, 1.51, and 1.46 mg/L at K1, K2, K3, and K4 stations, respectively. Specific UV absorbance indicated that organic matters of water are mostly hydrophilic and have low aromatic content. In seasonal pesticide monitoring, 71 different compounds were detected in water samples. The compounds whose concentrations exceeded Turkish Environmental Quality Standards were identified as DDD-op, DDE-p.p', diflufenican, and imidacloprid. Pesticides constitute most of the micropollutants detected in water samples. The highest positive correlation among water quality parameters was obtained between conductivity and nitrate (0.81) and total nitrogen (0.88).

Gas generation potential and pore characteristics of Jurassic lacustrine shale containing type Ⅱ kerogen: A case study of the Yabulai Basin, northwestern China

Jurassic lacustrine shales containing kerogen types Ⅱ and Ⅲ are widely distributed in sedimentary basins around the world. Previous studies on gas generation potential and pore characteristics of Jurassic lacustrine shales mainly focused on type Ⅲ kerogen, but ignored the systematic study of the shales containing type Ⅱ kerogen. This led to a poor understanding of the gas generation potential and pore characteristics of Jurassic lacustrine shales, which limits the effective exploration and development of shale gas. Taking the Lower Xinhe (J2x1) shale of the Yabulai Basin in northwestern China as the research object, this paper examines the gas generation potential and pore characteristics of a Jurassic lacustrine shale containing type Ⅱ kerogen. The J2x1 shale is largely classified as a very good source rock, kerogen is predominantly type Ⅱ, with thermal maturity ranging from mature to highly over-mature. The J2x1 shale is characterized by low porosity and permeability, and high content of brittle minerals. Different from the Jurassic lacustrine shales containing type Ⅲ kerogen, the J2x1 shales have a large amount of interparticle and intraparticle dissolution pores in the clay minerals as well as organic pores. The porosity and pore structure of the J2x1 shale are strongly controlled by total organic carbon (TOC) content. The methane adsorption capacity of the J2x1 shale is in the range of 2.10–2.99 m3/t, which is controlled by TOC content, clay mineral content, temperature and pressure. The geochemical characteristics, mineral composition and adsorption capacity suggest that the J2x1 shale has good shale exploration and development potential. A mathematical model is established to describe the various characteristics of methane adsorption capacity with depth and TOC content. The methane adsorption capacity of the J2x1 shale first increases and then decreases with increasing depth, with the depth corresponding to the maximum methane adsorption increases with increasing TOC content. When the TOC values of the J2x1 shale are mainly between 1% and 10%, the corresponding depth of the maximum methane adsorption capacity is 400–800 m, and the adsorption amount of the shale tends to minimize at a depth range of 2600–5100 m. The favorable shale gas exploration depth of the J2x1 shale in the study area increases with increasing TOC content. This research provides a geological reference for the exploration of this Jurassic shale gas in the Yabulai Basin, and the relevant experimental data provide important parameters for the numerical simulation of shale gas reservoirs in the study area. Moreover, the results of this study also provide an important reference for other basins in northwestern China, as well as continental basins with similar geological conditions in other regions.

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.

The environmental transformation mechanism of the coal- and oil shale-bearing interval in the Eocene Dalianhe Formation, Yilan Basin, Northeast China

Assemblages of multiple organic matter (OM)-related sedimentary energy systems are common in the Eocene nonmarine basins of Northeast China. During the Middle Eocene Climatic Optimum, oil shale developed in large quantities in the Yilan Basin. Numerous scientific papers have concentrated on the sedimentary cycle and industrial quality of the coal- and oil shale-bearing intervals, whereas few studies have studied the genetic environmental transformation mechanism of the coal and oil shale deposits. The Dalianhe Formation cover thick oil shale member and coal unit, which is a natural archive for studying the environmental evolution of lake swamp systems. In the present paper, the thermal maturity of organic matter (OM), oil shale industrial quality, coal rank, source of OM and paleoenvironmental conditions associated with OM accumulation in the Yilan Basin are investigated through bulk geochemical analyses, organic maceral analyses and biomarker composition analyses. The coal in the Yilan Basin is classified as subbituminous coal with high total organic carbon (TOC) values, high oil yields, low ash yields, and type II OM. The quality of the low-maturity oil shale in the Coal-Bearing Member is better than that in the Oil Shale Member. The oil shale in the Yilan Basin has type I-II OM and relatively high oil yields, which corresponds to the considerable content of liptinite with a predominantly alginite composition. Based on the higher Pr/Ph values, coal was deposited under oxic–dysoxic conditions, and the OM in the coal mainly originated from terrestrial plants, whereas the oil shale accumulated in a dysoxic environment with lower Pr/Ph values, and featured mixed OM sources, including terrestrial plants and low aquatic organisms. Affected by lake level fluctuations and wide peat swamping, the thickest and highest-quality coal and oil shale developed in swamps under a dysoxic–oxic water column in freshwater environments. Subsequently, the lake basin expanded rapidly, and the sedimentary environment changed to a dysoxic–oxic semideep–deep lake, in which extremely thick mudstone and a large amount of inferior oil shale with low oil yields accumulated under the influence of gravity flows. The basin continued to rapidly subside, the water column became anoxic–dysoxic, and the deposition of mudstone, siltstone and fine sandstone predominated.

Controls on preservation of organic matter during the Cenomanian Ocean Anoxic Event II (OAE2) and Turonian global sea-level rise: Agadir Basin, Morocco

The Ocean Anoxic Event II (OAE2) was a significant global event associated with a positive carbon isotope excursion, occurring from the Late Cenomanian to the Early Turonian (C/T). It has been commonly associated with enhanced organic carbon preservation. Carbon isotopic analysis carried out over the C/T interval in the Agadir Basin, Morocco, integrated with previous biostratigraphic data, allows a refined correlation of the OAE2 interval. Detailed sedimentary facies analysis identifies ten lithofacies that record the transition from shallow marine environments in the Late Cenomanian to relatively deeper conditions in the Early Turonian. The variation in lithofacies can be correlated to relative sea level changes that show a correlation to the global eustatic curve.The OAE2 interval comprises dark grey mudstones beds that display low total organic carbon (TOC) values. Trace element and facies analysis suggest dilution from high detrital influx, along with oxic water conditions and low productivity. OM-rich black mudstones are identified in post-OAE2 Early Turonian strata. Trace element analysis suggests this increase in organic matter accumulation was related to increased sea surface productivity and oxygen-depleted bottom water conditions, which facilitated organic matter preservation. Deposition of OM-rich black mudstones is widely reported during the global Early Turonian marine transgression, suggesting the very high sea level was a major control on organic matter generation and preservation.

Microbial attributes as structural quality index for physical health of an Oxisol under compaction levels

Microbial activity is a sensitive indicator of soil structure improvement provided by plant species in the physical recovery of compacted soils. This study aimed to assess the impacts of crop species on soil aggregate classes for soil recovery after compaction and identify which microbial attributes best describe the structural quality index for soil physical health in an Oxisol under no-tillage. The experiment comprised three crop species—maize, ruzigrass, and black oats—cultivated under four degrees of compactness produced by chiseling or machine traffic under long-term no-tillage. Soil aggregates were separated by dry sieving into five diameter classes to assess the basal respiration, microbial biomass carbon, metabolic quotient for CO2 (qCO2), labile carbon, cellulase activity, and total organic carbon. The values of microbial indicators for the bulk soil were estimated as a weighted mean of each attribute using aggregate size distribution. The lowest values for total organic carbon, labile carbon, and microbial biomass carbon were observed in aggregates > 4 mm. The basal respiration values increased from 8.2 µg C-CO2 g d−1 in the aggregates > 4 mm, to 22.1 µg C-CO2 g soil d−1 in the aggregates < 0.5 mm (+170%). Similarly, the cellulase activity increased approximately four times comparing aggregates > 4 mm (38 µg glucose g−1 d−1) to those < 1 mm (181 µg glucose g−1 d−1). The total organic carbon and microbial biomass carbon were found to be little affected by crops. However, the plots cultivated with black oats or ruzigrass exhibited higher cellulase activity, basal respiration, and qCO2 in comparison with maize, primarily due to the greater content of labile carbon. Increasing the mean weight diameter from 3 mm to 8 mm led to a decrease in the labile carbon (−27.4%), microbial biomass carbon (−25.5%), cellulase activity (−70%), and basal respiration (−21.6%), thereby revealing negative effects of soil compaction on microbial attributes. The degree of compactness did not influence the values of total organic carbon and qCO2. The response of the microbial indicators depends on the aggregate diameter classes. The results of this study indicate that cultivation of cover crops decreases the negative impacts of soil structure degradation on soil microbial quality. Cellulase activity and labile carbon were considered as new potential indicators of soil compaction for soil physical health studies—highly sensitive and quickly responsive to managements that induce soil structure changes in an Oxisol.

A new spatial estimation model and source apportionment of aliphatic hydrocarbons in coastal surface sediments of the Nayband Bay, Persian Gulf

Hydrocarbons, originating from oil and gas industries, are considered a potential risk for Nayband Bay, a natural marine park with extended mangroves, located on the north coastlines of the Persian Gulf, Iran. This paper determines the potential sources and spatial distribution of hydrocarbons, especially aliphatic hydrocarbons (AHCs), in Nayband Bay through the simultaneous application of three indices in the coastline surface sediments. To this end, a field study was conducted in the inter-tidal coastal zones and wetlands. Sediment samples were taken from surface layers along four transects with four sampling points at different distances from the gulf. The hydrocarbon compounds of the samples including AHCs, total petroleum hydrocarbons, and heavy metals (Ni, V as crude oil indicators) were analyzed and classified to discover the pollution indicators. Pearson pairwise correlation and cluster analyses along with pollution indices were employed to describe the spatial distribution pattern of hydrocarbons, identify hot spots, and determine the potential origin of AHCs. Different interpolation scenarios based on topographic and oceanic features were proposed to detect the spatial dynamics of AHCs. The results revealed that hydrocarbons mainly originated from anthropogenic sources including oil and gas industries located far from the affected area. It was also concluded that the long-distance pollution transfer was based on oceanic currents and wind direction in the bay. The proposed scenarios showed that the mean concentration values of total organic carbon and total organic material vary in the range 0.19 ppm to 0.4 ppm and 2.88 ppm to 3.20 ppm, respectively.

Geophysical prediction of organic matter abundance in source rocks based on geochemical analysis: A case study of southwestern Bozhong Sag, Bohai Sea, China

The Bozhong Sag is the largest petroliferous sag in the Bohai Bay Basin, and the source rocks of Paleogene Dongying and Shahejie Formations were buried deeply. Most of the drillings were located at the structural high, and there were few wells that met good quality source rocks, so it is difficult to evaluate the source rocks in the study area precisely by geochemical analysis only. Based on the Rock-Eval pyrolysis, total organic carbon (TOC) testing, the organic matter (OM) abundance of Paleogene source rocks in the southwestern Bozhong Sag were evaluated, including the lower of second member of Dongying Formation (E3d2L), the third member of Dongying Formation (E3d3), the first and second members of Shahejie Formation (E2s1+2), the third member of Shahejie Formation (E2s3). The results indicate that the E2s1+2 and E2s3 have better hydrocarbon generative potentials with the highest OM abundance, the E3d3 are of the second good quality, and the E3d2L have poor to fair hydrocarbon generative potential. Furthermore, the well logs were applied to predict TOC and residual hydrocarbon generation potential (S2) based on the sedimentary facies classification, using ΔlogR, generalized ΔlogR, logging multiple linear regression and BP neural network methods. The various methods were compared, and the BP neural network method have relatively better prediction accuracy. Based on the pre-stack simultaneous inversion (P-wave impedance, P-wave velocity and density inversion results) and the post-stack seismic attributes, the three-dimensional (3D) seismic prediction of TOC and S2 was carried out. The results show that the seismic near well prediction results of TOC and S2 based on seismic multi-attributes analysis correspond well with the results of well logging methods, and the plane prediction results are identical with the sedimentary facies map in the study area. The TOC and S2 values of E2s1+2 and E2s3 are higher than those in E3d3 and E3d2L, basically consistent with the geochemical analysis results. This method makes up the deficiency of geochemical methods, establishing the connection between geophysical information and geochemical data, and it is helpful to the 3D quantitative prediction and the evaluation of high-quality source rocks in the areas where the drillings are limited.

Source Rock Evaluation of Hydrocarbons in Deep-Water Offshore Areas Based on a BP Neural Network

Due to the lack of drilling data and poor quality of seismic data in deep-water offshore areas, conventional methods cannot effectively predict the total organic carbon (TOC) content. In this paper, the BP neural network method is used to predict the TOC of the strata overlying the target layer, which adds to the TOC information in the study area. Then, the highest TOC value of the strata overlying the target layer is used to select the most sensitive seismic attributes. Finally, the sensitive seismic attributes are used to evaluate the source rocks with no or few wells. A set of TOC prediction technology flows is established for TOC combined with seismic attributes under the condition of no wells and few wells in deep-water areas. The application example shows the reliability of TOC prediction by this technical process, and the study has a certain reference significance for the evaluation of hydrocarbon source rocks in offshore deep water.

Source Rock Evaluation from Rock to Seismic Data: An Integrated Machine-Learning-Based Work Flow and Application in the Brazilian Presalt (Santos Basin)

The capacity to predict the occurrence and quality of source rocks in a sedimentary basin is of great economic importance in the evaluation of conventional and non-conventional petroleum resources. Direct laboratory examinations of rock samples are the most accurate way to obtain their geochemical properties. However, rock information is usually sparse, and source rocks are often sampled at positions that may not be representative of the average organic content and quality of oil kitchens. This work proposes a work flow supported by machine learning methods (random forest, DBSCAN, and NGBoost) to automate the source rock characterization process to maximize the use of available data, expand data information, and reduce data analysis time. From the automated quality control of the input data through the extrapolation of laboratory measurements to continuous well logs of geochemical properties, culminating in the 3D estimation of these properties, we generate volumes of total organic carbon (TOC) by applying machine learning techniques. The proposed method provides more accurate predictions, reducing uncertainties in the characterization of source rocks and assisting in exploratory decision making. This methodology was applied in the presalt source rocks from Santos Basin (Brazil) and allowed us to quantify the TOC distribution, improving the interpretation of the main source rock interval top and base based only on seismic amplitude data. The result suggests higher TOC values in the northern and western grabens of the studied area and a higher charge risk in the eastern area.