S2 Value Research Articles

Comparison of the Backbone Dynamics of Dehaloperoxidase-Hemoglobin Isoenzymes.

Dehaloperoxidase (DHP) is a multifunctional hemeprotein with a functional switch generally regulated by the chemical class of the substrate. Its two isoforms, DHP-A and DHP-B, differ by only five amino acids and have an almost identical protein fold. However, the catalytic efficiency of DHP-B for oxidation by a peroxidase mechanism ranges from 2- to 6-fold greater than that of DHP-A depending on the conditions. X-ray crystallography has shown that many substrates and ligands have nearly identical binding in the two isoenzymes, suggesting that the difference in catalytic efficiency could be due to differences in the conformational dynamics. We compared the backbone dynamics of the DHP isoenzymes at pH 7 through heteronuclear relaxation dynamics at 11.75, 16.45, and 19.97 T in combination with four 300 ns MD simulations. While the overall dynamics of the isoenzymes are similar, there are specific local differences in functional regions of each protein. In DHP-A, Phe35 undergoes a slow chemical exchange between two conformational states likely coupled to a swinging motion of Tyr34. Moreover, Asn37 undergoes fast chemical exchange in DHP-A. Given that Phe35 and Asn37 are adjacent to Tyr34 and Tyr38, it is possible that their dynamics modulate the formation and migration of the active tyrosyl radicals in DHP-A at pH 7. Another significant difference is that both distal and proximal histidines have a 15-18% smaller S2 value in DHP-B, thus their greater flexibility could account for the higher catalytic activity. The distal histidine grants substrate access to the distal pocket. The greater flexibility of the proximal histidine could also accelerate H2O2 activation at the heme Fe by increased coupling of an amino acid charge relay to stabilize the ferryl Fe(IV) oxidation state in a Poulos-Kraut "push-pull"-type peroxidase mechanism.

Normal value and changes in CRP values on maternal and fetal umbilical cord blood with the labor and intrapartum interventions

Introduction: C-reactive protein (CRP) is widely used as an inflammatory marker. Since labour is an inflammatory process, CRP values vary during the intrapartum and postpartum period due to multiple factors.Methods: A descriptive-analytical study was carried out at Castle Street Hospital for Women. Mothers who have term singleton pregnancies with uneventful antenatal periods and have undergone vaginal delivery were recruited for the study. Samples were obtained just after admission to the labour ward (S1), 24 hours after the delivery (S2), and the fetal umbilical cord blood (S3). Reference ranges for S2 and S3 were determined using the interquartile range (IQR).Results: Out of 300 mothers recruited for the study, the mean age was 26.73 years (95% Confidence interval 19.5-36.9). There were 266 samples of S1,177 samples of S2, and 173 samples of S3 were collected. The reference range for S2 is 12.70-150.83 mg/dl, and for S3 is 0.1-8.1 mg/dL. The S2 value is significantly associated with duration of labor (r=0.47, p=0.046), number of vaginal examinations (VEs) (p < 0.001), augmentation of labor (AOL) (p=0.001), method of cervical ripening (p=0.014) and intrapartum intervention (p < 0.001). The number of vaginal examinations (p=0.02) and augmentation of labor (p=0.025) are significantly associated with fetal umbilical cord blood (S3).Conclusion: Early postpartum CRP can be risen up to 151 mg/dL after 24 hours of vaginal delivery. It may be associated with prolonged labor, number of VEs performed, AOL, method of cervical ripening, and episiotomy. Fluctuation of normal CRP values during the periods of antenatal, intrapartum, and postpartum needs to be assessed in the Sri Lankan community.

Sedimentary environment and controlling factors of carotane development: a case study of Linhe Depression in Hetao Basin

Carotane is a good indicator in sedimentary environment and oil-source correlation. γ-carotane and β-carotane are important biomarkers of source rocks in Linhe Formation, Linhe Depression, Hetao Basin. In this study, 22 mudstone samples were collected, and total organic carbon, rock-eval pyrolysis and Saturated hydrocarbon gas chromatography-mass spectrometry experiments were carried out to determine the hydrocarbon potential of Linhe Formation source rocks and the controlling factors for the development of carotane. Total Organic Carbon (TOC wt%) of the samples value 0.44-1.90%, and S1+S2 value 0.46-10.39mgHC/g Rock. The organic matter types are mainly type II1 and type II2, which are in the low mature-maturity stage, indicating that the source rocks have high hydrocarbon potential. Pr/Ph values 0.14-1.76, Gam/C30H values 0.11-1.89, C27/C29 values 0.28-0.69, indicating a strong reduced brackish water-brackish sedimentary environment. The source material was mainly higher plants, with less aquatic bacteria and algae. In the strong reducing environment of salt water, the bloom of algae and bacteria is conducive to the development of carotane, which is basically not affected by maturity. This study enriches the study of geochemical system of source rocks and provides a new case for the study of sedimentary environment of oil and gas basins in the world.

Petroleum Retention, Intraformational Migration and Segmented Accumulation within the Organic‐rich Shale in the Cretaceous Qingshankou Formation of the Gulong Sag, Songliao Basin, Northeast China

AbstractIn this study, organic geochemical and petrological analyses were conducted on 111 shale samples from a well to understand the retention, intraformational migration and segmented accumulation (shale oil enrichment in different intervals is unconnected) features of shale oil within the organic‐rich shale in the Qingshankou Formation of the Gulong Sag. Our study shows that retained petroleum characteristics in the investigated succession are mainly influenced by three factors: organic richness, intraformational migration and segmented accumulation. Organic matter richness primarily controls the amount of retained petroleum, especially the ‘live’ component indicated by the S2 value rather than the total organic carbon (TOC) figure alone. The negative expulsion efficiencies determined by mass‐balance calculations of hydrocarbons reveal that petroleum from adjacent organic‐rich intervals migrates into the interval of about 2386–2408 m, which is characterized by high free hydrocarbon (S1), OSI and saturated hydrocarbons content, along with a greater difference in δ13C values between polar compounds (including resins and asphaltenes) and saturated hydrocarbons. The depth‐dependent heterogeneity of carbon isotope ratios (δ13C) of mud methane gas, δ13C of extracts gross composition (SARA), δ13C of kerogen and SARA content of extracts suggest that the studied succession can be subdivided into four intervals. The shale oil sealing enrichment character in each interval is further corroborated by the distinct δ13C values of mud methane gas in different intervals. Due to the migration of petroleum into the 2386–2408 m interval, the S1, OSI and saturated hydrocarbons content of the interval show higher relative values. The maturity of organic matter in the 2471–2500 m interval is at the highest with the smaller size molecular components of the retained petroleum. Thus, favorable ‘sweet spots’ may be found in the 2386–2408 m interval and the 2471–2500 m interval, according to the experiment results in this study.

Reservoir characterization of the shallow to deep Longmaxi formation in the Weiyuan Block, southwestern Sichuan Basin

Marine shale gas exploration targets are reaching into shallow to deep or ultradeep burial depths. Rock microstructure and reservoir quality emerge as the main risk considerations for a profitable reservoir at these large depths. Shallow to deep marine shales occur in the Silurian Longmaxi Formation of the Weiyuan Block, which is located on the southwestern margin of the Sichuan Basin. However, few details of the characteristics of the Longmaxi shales in this Block have been reported. In this study, five wells approximately 3500 m deep were drilled. Field emission scanning electron microscopy, low-pressure gas adsorption and core plug porosity-permeability measurements are conducted on 6 shallow (2651–2940 m) and 11 deep (3539–3575 m) Longmaxi samples to obtain the organic geochemical characteristics, mineral constitutions, pore structures and petrophysical properties, and they are the major controls on reservoir quality. The results show similar mineralogical and organic geochemical characteristics in all samples from the various depths. Both shallow and deep shales are mainly composed of quartz, carbonate and clays and have a total organic carbon (TOC) content more than 2 wt.% and a mean S1 + S2 value more than 52 mg/g. Source rock quality criteria using the TOC and S1 + S2 suggest most shale samples fall excellent source rocks. The samples are mostly siliceous rocks that contain organic pores, intraparticle dissolution pores, interparticle quartz pores and interparticle clay pores and they play a positive role in improving reservoir quality. Pore surface area and pore volume increase with increasing TOC, indicating that the porous organic fraction is a major control on pore structure and porosity. We suggested that siliceous deep Longmaxi formation in Weiyuan Block belongs to a high-quality shale with an average TOC value of 3.9 wt.% and well-developed pore networks, which should be the important target for deep shale gas exploration.

A comparison of functional vestibulo-ocular reflex and proprioception in athletes of combat sports and ball sports

BackgroundThe contribution and role of sensory systems in providing postural control may vary depending on the condition or activity. Vestibulo-ocular reflex (VOR) and proprioception might be affected by the type of sport. ObjectiveThis study aimed to compare athletes engaged in combat sports and ball sports in terms of functional VOR and proprioception. DesignThis study is a cross-sectional, comperative research. MethodTwenty-four athletes engaged in combat sports and 20 in ball sports were included in the study. Functional examination of VOR in athletes was performed with a novel Functional Head Impulse Test (fHIT). Proprioception analysis was evaluated using Laser Pointer Assisted Angle Reproduction Test (LPA-ART) in 90° shoulder flexion and abduction. ResultsfHIT lateral and posterior % Correct Answer (CA) values and anterior SCC 6000°/s2 values of athletes engaged in ball sports were found to be statistically significantly higher than athletes in combat sports (p < 0.05). Except for anterior SCC 4000°/s2 value, scores of the ball players in all accelerations and directions were higher than combat sports athletes, although it was not statistically significant. The 90° shoulder flexion and abduction angle deviation values obtained from the LI-ATT were statistically lower in those who played ball sports (p < 0.05). ConclusionsParticipation in sports branches played with the ball is expected to provide gains for athletes who want to reach high-level performance in proprioceptive and vestibular functioning and those with vestibular/proprioceptive pathology. Maintaining clear vision in dynamic sports branches can be improved by training VOR function.

Petrographic, mineralogical, morphological and organic constraints of the Permian shaly-coal in the Tuli Basin of Limpopo-Area Karoo-Aged basin, South Africa: Implication for potential gas generation

The transition to a low-carbon energy source from coal has become imperative to mitigating the escalating climate change crisis. This study aims to investigate the organic-rich shale core samples of the Limpopo-Area Karoo Basin, retrieved from the borehole at depth 480–580 m. These samples were subjected to petrographic, mineralogical, morphological, and kerogen-type analysis to investigate potentials for shale gas generation. The petrographic analysis reveals maceral group mainly comprised of vitrinite group with some liptinite and inertinite and mineral compositions. The preponderance of pyrite framboids (1.6–12%) indicate redox of FeS2 as a precursor to methane gas generation in anoxic condition. The x-ray diffractometer (XRD) reveals the presence of quartz, albite, microcline, dolomite, pyrite and clay minerals which alluded to the mineral composition indicated by the petrographic analysis. The clay mineral component consists of montmorillonite, illite, chlorite, and mixed layered illite/smectite (I/S) in the Madzaringwe samples. The representative scanning electron microscopy-Energy Dispersive X-ray (SEM-EDX) images of the studied shales depict a combination of organic-matter, groundmass mineral, micro-fracture pore structures reflecting polyframboidal pyrite and carbonate dissolution morphology. The total organic carbon (TOC) contents averaging at 47 wt%, indicating an excellent source rock. The Rock-Eval 6 programmed pyrolysis samples showed S2 value (15.25–16.47 mg HC/g rock) with an average of 15.69 mg HC/g rock and Hydrogen index (HI) (34.0–37.0 mg HC/g TOC) indicating a Type-III Kerogen dominance prone to gas generation. The shale showed Tmax values (464–470 °C) averaging at 467.2 °C, yielding a thermally mature condensate wet-gas. This study reveals that the Permian carbonaceous rock tends to generate gas which can be hosted mainly by the organic matter pore structures, inorganic and micro-fracture pore structures.

Predicting protein flexibility with AlphaFold.

AlphaFold2 has revolutionized protein structure prediction from amino-acid sequence. In addition to protein structures, high-resolution dynamics information about various protein regions is important for understanding protein function. Although AlphaFold2 has neither been designed nor trained to predict protein dynamics, it is shown here how the information returned by AlphaFold2 can be used to predict dynamic protein regions at the individual residue level. The approach, which is termed cdsAF2, uses the 3D protein structure returned by AlphaFold2 to predict backbone NMR NH S2 order parameters using a local contact model that takes into account the contacts made by each peptide plane along the backbone with its environment. By combining for each residue AlphaFold2's pLDDT confidence score for the structure prediction accuracy with the predicted S2 value using the local contact model, an estimator is obtained that semi-quantitatively captures many of the dynamics features observed in experimental backbone NMR NH S2 order parameter profiles. The method is demonstrated for a set nine proteins of different sizes and variable amounts of dynamics and disorder.

Particular features of the thermoelectric power factor of encapsulated structures formed by two-dimensional layers

Model approach is used to obtain expression for the thermoelectric power factor sigma S2 (sigma --- is the static conductivity, S --- is the Seebeck coefficient), characterized monoatomic 2D layer of IV group elements, placed between two slabs, formed by hexagonal 2D layers of III-V com-pounds. The h-BN/graphene/h-BN structure is thoroughly studied and the dependence of the sigma S2 value on the chemical potential μ is examined. The analytical estimates of the function sigma S^2(μ) are given. Keywords: static conductivity, Seebeck coefficient, hexagonal monoatomic 2D layers.

Research on the Homogenization Evaluation of Cemented Paste Backfill in the Preparation Process Based on Image Texture Features

In China, cemented paste backfill (CPB) is a common treatment method after the exploitation of basic energy. The homogeneity of slurry influences the performance of CPB. However, the online monitoring and characterization of homogeneity lack relevant technologies and unified standards. This article discusses an online image analysis technique applied to the online monitoring of cemented paste backfill mixing, which is based on the evolution of the texture of images taken at the surface of the mixing bed. First, the grayscale distribution of the image obtained by the high-speed camera in the CPB preparation process was analyzed by Matlab and its variance (s2) was solved, and the texture features of the image were analyzed by the variance of grayscale distribution. Then, a homogeneity discriminant model (cst) was established. The results show that the variance value of the grayscale distribution of the slurry image increases rapidly at first, then gradually decreases, and becomes stable in the final stage since it turns a constant value. When the s2 value tends to be stable, the slurry gradually reaches homogenization, and the discriminant coefficient of paste homogenization based on the homogenization discriminant model reaches 0.05. The homogenization prediction of CPB proves to be consistent with the backfill performance comparison results. The evolution of the texture allows obtaining important information on the evolution of different formulations during mixing, which can be used for intelligent monitoring of CPB preparation process.

Effect of para substituents on magnetic properties of azido-Cu(II) complexes with benzoate/azide coligands: A theoretical perspective

The introduction of benzoic acid with different para substituents into the azido-Cu(II) complex can fine-tune the structure of the complex and regulate its magnetic properties. We constructed 22 azido-Cu(II) complexes, optimized their structure at the B3LYP/def2-TZVP level of theory, and studied their magnetic properties at the B3LYP/ZORA-def2-TZVPP level of theory. Results indicate that as the S2 value between non-orthogonal magnetic orbitals gradually increases with the introduction of substituents, the contribution of the antiferromagnetic part to the magnetic coupling constant Jcalc becomes larger, and the Jcalc gradually decreases. We performed spin population analysis and identified two superexchange pathways for these dinuclear complexes and established a relationship between the average Mulliken charge of the carboxylate oxygen atoms and Jcalc. The understanding of the mechanism through which the substituent effect regulates the magnetic properties of complexes provides a theoretical basis for the informed synthesis of azido-Cu(II) complexes.

Variations of lacustrine shale reservoirs in different deformation zones of Mohe Basin, northeastern China: Insights into the impact of thrust nappe structure on shale gas preservation

The structural preservation conditions are crucial for shale gas accumulation and preservation. In this study, the Emuerhe thrust nappe structural belt in the Mohe Basin is taken as an example to investigate the influence of the thrust nappe structure on shale reservoir quality. According to the rock metamorphic characteristics and deformation degree, the thrust nappe belt is divided into the root zone, middle zone, and front zone. Based on the observations of field outcrops, cores, and thin sections, the hydrocarbon generation capacity and reservoir properties of shale in different units were investigated through an integrated analysis of organic geochemical data, X-ray diffraction, low-pressure CO2 and N2 adsorption, and helium porosity measurements. Furthermore, implications for shale gas preservation are discussed. Owing to the influence of high temperature and pressure caused by dynamic metamorphism, the Ro value of shales in the root zone exceeds 5.5%, which is far beyond the theoretical upper limit of hydrocarbon generation potential. Thus, the hydrocarbon generation potential of shales exhibits an opposite trend to the deformation strength of the Emuerhe thrust nappe belt. The S1+S2 value of shales within the root zone and middle zone is generally lower than 0.3. The primary pore structure of shales in the root zone was changed or destroyed by ductile shearing and mylonitization. Furthermore, dynamic metamorphism led to a significant decrease in the adsorption capacity of shales. Both the micropores and mesopores in these shales are very limited, and the storage space is relatively low. The strong compaction caused by the thrust nappe tectonic led to a reduction in the pore size. Thus, pores with diameters <10 nm dominated the main reservoir space, and the porosity of shales in the middle zone was lower than that in the root zone. The influence of thrust nappe tectonics on the front zone was relatively weak. Overall, the shales exhibited good hydrocarbon generation potential, high specific surface area, and pore volume. The pore–fracture system consists of relatively large pores, and the extensional fractures are favorable for enhancing the physical properties of shale reservoirs in the front zone. The strong thrust nappe resulted in caprock that experiences broad uplift-erosion and fault failure. The original structure of the shale can be changed or destroyed by ductile shearing and strong compaction. Heating-up caused by tectonics could also promote the rapid desorption of shale gas, which can lead to poor self-sealing performance of shale. The hydrocarbon generation capacity, reservoir property, and preservation conditions of shale display an improving trend along the thrust direction of the Emuerhe thrust nappe structural belt.

Residue interaction networks of K-Ras protein with water molecules identifies the potential role of switch II and P-loop

The mutant K-Ras with aberrant signaling is the primary cause of several cancers. The proposed study investigated the influence of water molecules in K-Ras crystal structure, where they have a significant function by understanding their residue interaction networks (RINs). We analyzed the RINs of K-Ras with and without water molecules and determined their interaction properties. RINs were developed with the help of StructureViz2 and RINspector; further, the changes in K-Ras backbone flexibility were predicted with the DynaMine. We found that the residues K42, I142, and L159 are the hotspots from water, including the K-Ras-GTP complex with the highest residue centrality analysis (RCA) Z-score. The DynaMine prediction calculated the NMR S2 value for the frequently mutated positions G12, G13, and Q61 showing a minor shift in flexibility, which make up the P-Loop and switch II of the K-Ras protein. This flexibility shift can account for changes in conformational activity and the protein's GTPase activity, making it difficult to recognize by the effectors and exchange factors. Taken together, our study helps in understanding the functional importance of the water molecules in K-Ras protein and the impact of mutation that modulate the conformational state of the protein.

Geochemistry and Mineralogy of Lower Paleozoic Heituao Shale from Tadong Low Uplift of Tarim Basin, China: Implication for Shale Gas Development

Tarim Basin is the largest Petroliferous basin in China, while its shale gas development potential has not been fully revealed. The organic-rich black shale in middle Ordovician Heituao Formation from Tadong low uplift of Tarim Basin has been considered as an important source rock and has the characteristic of large thickness, high organic matter content and high thermal maturity degree. To obtain its development potential, geochemical, mineralogical and mechanics research is conducted based on Rock-Eval pyrolysis, total organic carbon (TOC), X-ray diffraction (XRD) and uniaxial compression experiments. The results show that: (1) the TOC content ranges between 0.63 and 2.51 wt% with an average value of 1.22 wt%, the Tmax values are 382–523 °C (average = 468.9 °C), and the S2 value is relatively low which ranges from 0.08 to 1.37 mg HC/g rock (averaging of 0.42 mg HC/g rock); (2) the organic matter of Heituao shale in Tadong low uplift show poor abundance as indicated by low S2 value, gas-prone property, and post mature stage (stage of dry gas). (3) Quartz is the main mineral component in Heituao shale samples, accounting for 26–94 wt% with an average of 72 wt%. Additionally, its Young’s modulus ranges from 20.0 to 23.1 GPa with an average of 21.2 GPa, Poisson’s ratio ranges between 0.11 and 0.21 (average = 0.15); (4) the fracability parameter of brittleness index (BI) ranges between 0.28 and 0.99 (averaging of 0.85), indicating good fracability potential of Heituao shale of Tadong low uplift and has the potential for shale gas development. This study reveals the shale gas accumulation potential in middle Ordovician of the Tarim Basin, and beneficial for future exploration and production practice.

Assessing extreme maturities – Challenging examples from immature Jordanian to overmature Far Eastern unconventional formations

Thermal maturity is often readily available from optical vitrinite reflectance measurements, but in marine sediments with absence of terrigenous organic material (vitrinite macerals) or formations older than the Devonian, this technique has limitations. Raman spectroscopy has been applied as an alternative measurement to infer thermal maturity in challenging formations. Organic-rich outcrop samples from the Jordanian Lajjoun and Sultani deposits and from a Far East shale were characterized for their key geochemical properties (bulk chemical and mineral composition, total organic carbon content) and thermal maturity. Bulk mineral and chemical abundances were quantified using standard X-ray diffraction and X-ray fluorescence techniques. Total organic carbon (TOC) content was calculated from programmed temperature pyrolysis. Thermal maturity was determined and compared using conventional vitrinite reflectance and a novel, rapid laser Raman spectroscopy method. The Jordanian samples are organic-rich (16.3–17.4 wt% TOC), while the Far Eastern sample is relatively organic-lean (2 wt% TOC). Programmed pyrolysis shows that the Jordanian samples seem immature with high remaining hydrocarbon generative potential (S2), whereas the sample from the Far East appears to be overmature with extremely low S2 value. These findings were confirmed by the results from organic petrography as well as through Raman spectroscopic measurements. The Far Eastern samples are suggested to be highly mature (4.6–5.7% VRE), whereas the Jordanian samples were found to be immature (0.4–0.5% VRE). Robust Raman maturity determination allows to define and refine petrophysical properties of kerogen and thus enhance the accuracy in predicting hydrocarbon in place and the potential for its recovery.

Petrophysical and geochemical interpretations of well logs from the pre-Carboniferous succession in Barnicarndy 1, Canning Basin, Western Australia

Barnicarndy 1 is a stratigraphic well drilled in the southern part of the Canning Basin’s Barnicarndy Graben under Geoscience Australia’s Exploring for the Future program in collaboration with the Geological Survey of Western Australia to provide stratigraphic data for this poorly understood tectonic component. The well intersects a thin Cenozoic section, Permian–Carboniferous fluvial clastics and glacial diamictites and a thick pre-Carboniferous succession (855–2585mRT) unconformably overlying Neoproterozoic metasedimentary rocks. Three informal siliciclastic intervals were defined based on core lithology, well logs, chemical and mineral compositions: the Upper Sandstone (855–1348.1mRT), Middle Interval (1348.1–2443.4mRT) and Lower Sandstone (2443.4–2585mRT). The Middle Interval was further divided into six internal zones. Both conventional methods and artificial neural network technology were applied to well logs to interpret petrophysical and elastic properties, total organic carbon (TOC) content, pyrolysis products from the cracking of organic matter (S2) and mineral compositions. Average sandstone porosity and reservoir permeability are 17.9% and 464.5mD in the Upper Sandstone and 6.75% and 10mD in the Lower Sandstone. The Middle Interval claystone has an average porosity and permeability of 4.17% and 0.006mD, and average TOC content and S2 value of 0.17wt% and 0.047mgHC/g rock, with maximum values of 0.66wt% and 0.46mgHC/g rock, respectively. Correlations of mineral compositions and petrophysical, geomechanical and organic geochemical properties of the Middle Interval have been conducted and demonstrate that these sediments are organically lean and lie within the oil and gas window.

Source rock evaluation of Afowo clay type from the Eastern Dahomey Basin, Nigeria: insights from different measurements

The Cretaceous Afowo Formation in the Eastern Dohamey Basin is characterized by an admixture of lithofacies ranging from sandstones, claystones, shales, clays, sand/shale, and sand/clay intercalations. The sandy facies, a mix of sandstone, clay, shale, and intercalations, contain biodegraded hydrocarbons while the shales and claystones that underlie it are rich in organic matter. The hydrocarbon-bearing interval is commonly referred to as the oil sand or tar sand. In this study, Afowo clay type underlying an outcrop of the oil sand was appraised for its hydrocarbon potential with loss on ignition, thermogravimetry, and rock evaluation pyrolysis. Results obtained from loss on ignition showed that total organic matter content, a proxy to total organic carbon, for the Afowo clay type ranged from 9.410 to 38.750 wt%. The organic maturation temperature (Tmax) was determined using both thermogravimetry and rock evaluation pyrolysis (Rock–Eval). Thermogravimetric analysis produced reliable Tmax within the range of 417–424 °C for all the samples. The results from rock evaluation pyrolysis on the same samples showed that total organic carbon ranged from 0.81 to 18.46 wt% with Tmax ranging from 417 to 424 °C. It was not possible to determine Tmax for one of the samples with Rock–Eval due to a small S2 value (0.22 mg Hc/g). The variations in organic matter contents from loss on ignition agree with total organic carbon computed from rock evaluation pyrolysis; samples with high organic matter contents have corresponding high TOC values. This study demonstrates that loss on ignition and thermogravimetry could complement and augment rock evaluation pyrolysis data for petroleum source rock characterization.

The effect of volcanism to the source rock maturity in Gunung Endut area: Insight for subvolcanic hydrocarbon exploration

Banten region is known to have subvolcanic hydrocarbon system but no proven play despite oil seeps and the potential source rock have been identified in this area. A Geochemical analysis of source rock have been done on Gunung Endut, Banten Province. There are four coaly shale sample from Genteng Formation and Bojongmanik Formation collected and analysed in this study. The purpose of this study is to understand the influence of volcanic environment towards the quality, quantity and maturity of source rock based on TOC, pyrolysis, and vitrinite reflectance analyses. The result obtained showed TOC value between 8–18 wt% which indicated excellent petroleum potential from the source rock. In addition, Pyrolysis data showed S1 value between 0.05–0.19, S2 value between 1.52–11.53, S3 value between 4.10–7.57 and Tmax 414.8–523.2 °C. From both analyses, TOC and Pyrolysis, the source rock is categorized as Type 3 Kerogen producing gas and Type 4. Based on its maturity, three sample are categorized as immature while one specimen is categorized as postmature. Furthermore, Vitrinite Reflectance analysis result shows Ro value between 0.27–0.63 that support the result of pyrolysis analysis. Maturity anomaly found in the sample is presumed to be caused by intrusion that have been identified by the geological mapping in the same region. The condition on the surface may also reflect the source rock in the subsurface. A number of source rock in Banten region may be matured due to intrusion that related to volcanic activities. Subsurface zone with abundance igneous bodies will have different maturity compare to other area. Hence, it is important for petroleum exploration activities in Banten region or other volcanic area to properly identify the distribution of subsurface igneous body due to its effect to the source rock maturity.

Facies heterogeneity and source potential of carbonate-mudstone-dominated distal ramp deposits, Agrio Formation, Neuquén Basin, Argentina

ABSTRACTThe carbonate-mudstone-dominated Lower Cretaceous Agrio Formation is the youngest marine source rock of the hydrocarbon-prolific Neuquén Basin in Argentina, yet its facies variability and unconventional hydrocarbon potential remains relatively understudied. Detailed studies of mudstone facies variability in thick, carbonate mudstone successions deposited largely below storm wave base (i.e., chalk–marl, black shale, limestone), like the Agrio Formation, are rare and instead commonly focus on biostratigraphy or organic geochemistry alone. A continuous northern section of the Agrio Formation and a southern composite section of the lower Pilmatué and middle Avilé members, totaling ∼ 1,200 m of outcrop, were measured. From these measured sections, programmed pyrolysis (n = 339 samples), X-ray diffraction (XRD; n = 69), and thin sections (n = 69) were used to develop a high-resolution integrated macrofacies and microfacies scheme. The four most volumetrically abundant facies include detrital-quartz-silt-bearing fine mudstone (facies 1), radiolarian-bearing calcareous fine mudstone (facies 2), detrital-quartz-silt- and shell-bearing calcareous fine mudstone (facies 3), and calcareous wackestone (facies 4). All four facies are volumetrically dominated by carbonate mud matrix (i.e., micrite) that represents either 1) original pelagic coccolithophore deposition modified by diagenesis, 2) transported carbonate mud (i.e., bottom currents like contour currents or sediment gravity flows), or 3) a combination of both. Outcrop observations, XRD mineralogic trends, and petrographic variations in grain composition between detrital quartz silt, radiolarian and microfossil to macrofossil content (mainly benthic foraminifera and bivalves) distinguish the four mudstone facies. The facies scheme indicates distinctly more heterogeneous and current-influenced sedimentation in the downdip sub-storm wave base than previously described in the Agrio and in carbonate-dominated basinal settings in general. A depositional model is proposed for further testing that may prove valuable towards re-evaluating basinal carbonate mudstone successions worldwide. Utilizing TOC, S2, and HI value cutoffs, this study defines five discrete stratigraphic packages in the Agrio Formation that have the highest source potential, collectively totaling ∼ 140 m thick. The novel integration of macrofacies and microfacies analysis, stratigraphy, and a geochemical analysis allow both depositional insights and the assessment of a potential source rock. The study adds to a growing body of literature on 1) carbonate ramp (or slope) to basinal processes and 2) facies models for organic-rich, carbonate-dominated mudstone successions that are unconventional hydrocarbon systems.

Oil retention and intrasource migration in the organic-rich lacustrine Chang 7 shale of the Upper Triassic Yanchang Formation, Ordos Basin, central China

The Zhang 22 well was drilled in the Ordos Basin, penetrating the Chang 7 Member of the Triassic Yanchang Formation, which, cumulatively, has more than 80 m (>260 ft) of black organic-rich shale of oil window maturity. Using 76 samples collected every 1 m (3 ft) from the well, the effects of stratigraphic fractionation and petroleum expulsion within five intervals of the Chang 7 shale were qualitatively and quantitatively documented. The organic-rich intervals 1, 2, and 5, having an average total organic carbon (TOC) of 6.79 wt. % and pyrolyzable hydrocarbon potential of 9.40 mg/g rock (i.e., the amount of hydrocarbons generated by pyrolysis between 300°C and 650°C [S2]), are defined as “generative units” in the Chang 7 shale system, compared to the “in-source reservoirs” or “sweet spots” (i.e., the third and fourth intervals), which contain a lower average TOC of 4.19 wt. % and an average S2 value of 7.17 mg/g rock, but the highest amount of free oil (average total oil of 7.35 mg/g rock). Geochemical and molecular compositions display distinctive differences between samples from these source and reservoir groupings. For example, bitumens from the generative units proportionally possess lower saturated hydrocarbons (56%–66%) than those from the in-source reservoirs (up to 81%). The proportions of aromatic and polar compounds in the generative units are accordingly higher than in their counterpart. The individual molecular weight distribution of sample extracts displays more light-end moieties being enriched in the generative units. By applying the compositional mass balance calculation, the overall and compound-specific expulsion efficiencies in the in-source reservoirs are abnormally negative compared to the positive values in the generative intervals. This finding, in conjunction with the effects of the preferential retention of aliphatic hydrocarbons and the differential expulsion of light molecular weight compounds in the in-source reservoirs, indicates a short-distance intrasource migration of generated petroleum into the sweet-spot intervals (intervals 3 and 4) from the overlying units (intervals 1 and 2) and the underlying interval 5. Furthermore, when quantifying the total amount of retained petroleum in the shale system, an amended assessment has been introduced to overcome the systematic misestimations if only unextracted values for the amount of thermally extractable hydrocarbons volatilized at 300°C (mg HC/g rock) were considered. Thus, the oil crossover effect, temperature at which the rate of S2 generation is at maximum shift phenomenon, and the hydrogen index being shifted to higher values after extraction all account for identifying intervals 3 and 4 as the in-source reservoirs. In this study, we have not only identified a set of promising in-source targets for shale oil exploration and production, but we also presented the chemical and molecular composition for these shale oils. We have additionally speculated for the intrasource migration model and further discussed the different expulsion efficiencies in the shale system upon the compositional mass balance calculation as well as the stratigraphic fractionation on differentiating the chemical compositions during migration. The improved oil quality by fractionation, the extra storage potential derived from microfossil quartz, the weak adsorptive affinity of oil to organic matter, and the good shale susceptibility to hydraulic fracturing all give a promising prospective for exploring and producing shale oil from the Chang 7 shale system in the Ordos Basin.