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Breakthroughs in shale gas exploration in the Upper Ordovician-Lower Silurian strata of the Upper Yangtze Platform have attracted interest in its sedimentary-tectonic evolution, but the tectonic background of the northern margin of the Upper Yangtze Platform remains unclear. In this paper, the Wufeng-Longmaxi formations on the northern margin of the Upper Yangtze Platform were investigated. Based on geochemical and mineralogical analyses of the tuffs/K-bentonites of the Wufeng Formation and the barite in the Longmaxi Formation, as well as previous research results, it was concluded that the northern margin of the Upper Yangtze Platform was in an extensional tectonic background during the Late Ordovician-Early Silurian. Detailed analysis revealed that, (1) the U–Pb zircon age of the tuff in the Bajiaokou section in South Qinling is 443.91 ± 0.92 Ma. The Zr/TiO 2 –Nb/Y diagram of the tuffs/K-bentonites indicates that their protoliths were alkaline-subalkaline basalt and andesite series rock. Based on the Th–Hf/3-Ta, Th–Tb*3-Ta*2, and TiO 2 –Nb/3-Th diagrams, there are undiscovered intraplate tension calc-alkaline basalts in the northern Yangtze Platform or the southern Qinling region, which provided volcanic clastic materials to the Ziyang, Lan'gao, Chengkou, Yichang and other regions. (2) Scanning electron microscopy revealed that the barite crystals in the Longmaxi Formation exhibit dissolution features and have a large particle size. Energy spectrum analysis of these barite crystals revealed that they have C, O, S, and Ba contents of 8.48 wt%, 22.98 wt%, 13.09 wt% and 55.44 wt%, so they are speculated to have been formed via cold methane seep genesis in a weak extensional tectonic setting. The 87Sr/86Sr ratios of the barite revealed that different types of barite were simultaneously formed in this area under the influences of hydrothermal and cold methane seeps. (3) The analysis of the heavy minerals in the Lower Silurian strata in the Bajiaokou section revealed that the provenance in the South Qinling area changed significantly during the late Early Silurian. Based on the above analyses, the northern margin of the Upper Yangtze Platform was in an extensional tectonic setting during the Late Ordovician-Early Silurian. The distribution of the total organic carbon content indicated that the extensional tectonic background provided good conditions for the enrichment and preservation of organic matter. The results of this study provide an understanding of the regional sedimentary-tectonic pattern and evolution of the Yangtze Platform during this period, as well as a reference for future shale gas exploration in this region. • The tectonic background of the Late Ordovician-Early Silurian was studied. • The northern margin of the Upper Yangtze Platform is an extensional background. • The extensional tectonics caused the cold seepage events. • The extensional fault controlled the distribution of volcanic clastic sediments. • Organic matter accumulation was influenced by the extensional fault depression. [ABSTRACT FROM AUTHOR]

Ghana is recognised as one of the recent oil and gas producing countries in the Gulf of Guinea, West Africa. However, despite the significant hydrocarbon accumulation in the Western Basin of Ghana, not much is known about the current potential of source rocks in this Basin. To broaden the scope of current knowledge on the Western Basin of Ghana, this paper identifies the current formation potential, organic matter origin, thermal maturity, and possible ages within the Cretaceous Period for hydrocarbon generation in the basin, using geochemical techniques and statistical analyses of 1530 cuttings and core samples. The geochemical parameters include pyrolysis data such as free hydrocarbon (S 1), hydrocarbon generated (S 2), carbon dioxide released (S 3), hydrogen index (HI), production index (PI), maximum temperature (T max), oxygen index (OI) and total organic carbon (TOC). The formations encountered in the Western Basin, which have various ages within the Cretaceous Period , show a good to very good possibility of producing hydrocarbon with mainly kerogen type II/III and some amount of type I in certain formations. The majority of the Cretaceous ages fall in the early mature to peak maturity zone, with Campanian and Santonian considered as additional hydrocarbon sources to the Albian, Cenomanian, and Turonian. Pearson coefficient showed that TOC has a strong positive correlation with S 2 , positive correlation with S 1 and HI, and negative correlation with T max. Two-Step and K-means clustering on the studied samples show that TOC, S 2 , and S 3 are the major parameters for source rock potential prediction. Factor analysis gave three factors affecting source rock evaluation. Factor 1 highlights TOC, S 1, and S 2 as the parameters for identifying the quantity and quality of organic matter. This is confirmed by factor 2, which identifies HI and OI as the determining variables. Factor 3 identifies PI and T max as indicators of the thermal maturity of the source rock. • Cretaceous formations showed very good source rock hydrocarbon potential. • Source rock evaluation depends on thermal maturity and amount of organic matter. • Santonian and Campanian are very good formation source rocks. [ABSTRACT FROM AUTHOR]

The gas flow in the organic matter with multiple flow regimes is critical to the shale gas production from shale gas reservoirs, but simultaneously simulating the full flow regimes of shale gas in the nanopores of the fractal shale organic matter is still unavailable. This paper presents a modified lattice Boltzmann model with effective relaxation time to simulate the shale gas micro-flow behaviors in fractal organic matter for permeability prediction. Firstly, some fractal shale organic matters are reconstructed by the quartet structure generation set (QSGS) algorithm, and the structural parameters such as fractal dimension, lacunarity and average pore diameter are calculated to characterize the complexity of the fractal shale organic matter. Secondly, effective viscosity and Knudsen layer are introduced into the effective relaxation time to formulate a modified lattice Boltzmann model. Thirdly, this modified lattice Boltzmann model is verified by comparing with the theoretical permeability models for the gas flow in the body centered cubic (BCC) arrays. Finally, a series of gas flow simulations in reconstructed fractal shale organic matter are conducted to explore the effects of structure parameters on permeability. Numerical simulations show that the modified lattice Boltzmann model can simulate the full gas flow regimes and predict the permeability of the fractal shale organic matter. The logarithm of permeability is negatively linearly correlated with fractal dimension and positively linearly correlated with lacunarity of the shale organic matter. This permeability exponentially increases with the increase of average pore diameter and a power law is observed between the fractal dimension and average pore diameter of these fractal shale organic matters. The anisotropic structures have great impacts on the directional permeability of shale organic matter. The permeability k x in the horizontal direction increases first and then decreases with the increase of anisotropic ratio (AR) and reaches the peak when AR is about 20. The permeability k y in the vertical direction monotonically decreases with the increase of AR. • Effective viscosity and Knudsen layer are introduced into MRT LBM. • The effects of structural parameters on permeability of shale organic matter are revealed. • Full flow regimes of shale gas are simultaneously simulated by the modified MRT LBM. [ABSTRACT FROM AUTHOR]

Due to the similarity of the biomarker characteristics of the source rocks of different layers, the progress of the oil source research of the Yanchang Formation in the Ordos Basin is difficult and slow, which highlights the shortcomings of traditional research methods. Given this, this paper uses the gas chromatography-mass spectrometry analysis results of a large volume of samples of the Yanchang Formation in the basin as the dataset, and performs an exploratory application of the factor analysis (FA, a multivariate statistical method) to analyze the molecular geochemical characteristics of organic matter, with an aim to find features that have not been noticed in the past, and give a reasonable explanation for the oil source. The findings are summarized as below: with the help of multivariate (31 molecular geochemical parameters are introduced), FA can quantify many geochemical properties of samples well, which brings convenience to research. Based on the results, it was found that parameters such as C 26 TT/C 25 TT, sterane/hopane, and ΣC 19-26 TT/C 30 αβ can effectively distinguish the samples of different areas and layers, and it is further believed that the Chang 9 source rock has higher contributions to adjacent layers (mainly the Chang 8–Chang 10 oil groups) in areas where it is abundant (mainly the Wuqi-Zhidan area), while in the other areas and layers, oil is mostly attributed to the Chang 7 source rock. •Conventional oil-source research methods are inadequate when facing the Yanchang Fm. of Ordos Basin. •Exploratively combine factor analysis methods to analyze a large amount of GC-MS data. •Factor analysis effectively reveals differences in petroleum geochemistry among different source rocks. • This research has the potential value of promoting the development of petroleum geochemistry technology. [ABSTRACT FROM AUTHOR]

The upper Permian Longtan Formation (LTF) shale is a new shale gas exploration and development focus in China, which was formed in a transitional depositional environment. Because of the difference in the sedimentary environment between marine-continental transitional shale and marine shale, the enrichment characteristics and mechanism of organic matter (OM) are very different. Because of a weak research foundation, the enrichment mechanism of OM in the LTF shale in the Sichuan Basin is still unclear. In this paper, shale samples of the upper Permian LTF from the Well F5 were collected, and the abundance, source and sedimentary environment of organic matter were studied by using paleoclimate, detrital input, redox, paleoproductivity and sedimentation rate parameters. The results show that the TOC content of the LTF shale is high (average = 3.04%) and reaches the high to overmature stage (average = 2.46%), indicating a favorable source rock. The LTF shale was deposited in a humid and hot climate, which was conducive to the growth and prosperity of a large number of plants. The source of organic matter was mainly terrestrial plant fragments. The sedimentary environment of the LTF shale was oxic, it had a high sedimentation rate, which reduced the oxidation rate of OM, promoted the rapid deposition of OM, and ensured the preservation of organic matter. In summary, the enrichment of OM of LTF shale in the Sichuan Basin was affected by the sedimentary environment, which was complicated. The main controlling factors were detrital input, redox conditions and sedimentation rate. • The geochemical characteristics of Permian Longtan Formation (PLTF) shale in eastern Sichuan are analyzed. • The sedimentary paleoenvironment of PLTF shale in eastern Sichuan is reconstructed. • The main controlling factors of organic matter enrichment of PLTF in eastern Sichuan are studied for the first time. [ABSTRACT FROM AUTHOR]

In recent years, rock pyrolysis parameters combined with a mass balance method have been used to calculate the hydrocarbon expulsion efficiency. However, due to the experimental procedure of rock pyrolysis, the residual hydrocarbon amount (S 1) is underestimated, and the hydrocarbon-generation potential of kerogen (S 2) is overestimated, so that the hydrocarbon expulsion efficiency calculated from the pyrolysis parameters before correction is higher than the actual value. In this paper, the pyrolysis parameters were corrected by performing pyrolysis before and after the extraction of source rocks, and the hydrocarbon expulsion efficiency of the mudstone of the Qing 1 member of the Ha14 well in Songliao basin was calculated using the chemical kinetics method. The hydrocarbon expulsion efficiencies before and after the correction were considerably different, the hydrocarbon expulsion efficiency of the Ha14 well after correction was 17.5% lower than that before correction. The study show that the higher the abundance and maturity of source rock are, the higher the hydrocarbon expulsion efficiency is; the oil-type organic matter has a higher hydrocarbon-expulsion efficiency than the gas-type organic matter; the interbedded sand and mud type source-reservoir configuration relationship is beneficial to hydrocarbon expulsion; the underwater diversion channel phase has the highest hydrocarbon expulsion efficiency. • S 1 and S 2 need be corrected by the pyrolysis before and after chloroform extraction. • The HHE showed a positive correlation with TOC, Ro, and the oil-type kerogen. • The higher the ratio of sandstone to mudstone in the strata, the higher the HEE. [ABSTRACT FROM AUTHOR]

This paper presents the study of saturated biomarkers in maltenes and the compounds adsorbed and occluded by the asphaltenes of six Venezuelan crude oils. The study is intended to know to what extent geochemical information stored in the adsorbed and occluded compounds matches the information in maltenes when it comes to evaluating source input, depositional environment, and thermal maturity. Our findings suggest that geochemical information obtained from the adsorbed and occluded compounds agrees with the information provided by maltenes of unaltered crude oils such as Alturitas, Boscan, Guafita, and Silvestre. We confirmed a clear correlation of Alturitas and Boscan crude oils with a carbonate source rock sedimented under anoxic conditions and containing marine organic matter, while Guafita and Silvestre crude oils resulted from a marl-type source rock characterized by mixtures of marine and terrigenous organic matter inputs preserved under varying redox conditions (anoxic to sub-oxic). Regarding maturity, Alturitas and Silvestre resulted more mature than Boscan and Guafita. Despite the good correspondence between the geochemical information provided by the maltenes and the adsorbed and occluded compounds, we observed compound enrichments that caused limitations in the use of some geochemical indicators. The adsorbed compounds of the six studied crude oils were enriched in linear alkanes higher than n -C 24 , regular steranes (C 27 –C 28), and pentacyclic terpanes, while in the occluded compounds pregnanes, tricyclic terpanes, and n-alkanes higher than n -C 24 were more abundant. Thus, maturity relationships defined by the relative abundances of low and high molecular mass steranes and terpanes yielded values that confused when the adsorbed and occluded compounds were compared with the respective maltenes. However, when these relationships were used to compare the occluded compounds of two or more different crude oils, they yielded a reliable appraisal of the maturity stage of the respective source rock. Our results strongly suggest that the adsorbed compounds still preserve their geochemical information as they probably undergo a very low exchange with the surrounding maltenes. So, these compounds together with the occluded ones become a valuable source of geochemical information to assess altered crude oils such as Ayacucho and Junín that have lost most of their maltene biomarkers due to biodegradation. In these cases, the information provided by the adsorbed and occluded compounds confirmed that Ayacucho crude oil is more mature than Junín and that the former derives from a carbonate, marine-organic-matter source rock sedimented under anoxic conditions while the latter correlates with a marl-type source rock sedimented in anoxic conditions and containing mixtures of terrigenous and marine organic matter. Compounds such as oleanane, C 27 25,28,30-trisnorhopane (TNH), C 28 17α,21β,28,30-dinorhopane (DNH) and C 29 17α(H),21β(H)-25-norhopane (NH) detected in the occluded material of the six studied oils, indicate that the major contributions to the occluded compounds probably came from the original material initially adsorbed and occluded in the parent kerogen. [Display omitted] • Saturated compounds trapped by asphaltenes of six Venezuelan crude oils were studied. • The adsorbed compounds still preserved some geochemical information. • Compounds occluded by asphaltenes represent a less mature material. • Some saturated compounds are enriched in the adsorbed and occluded fractions. • Adsorbed and occluded compounds are sources of geochemical information. [ABSTRACT FROM AUTHOR]

In this paper, the original nature of organic matters is introduced for the first time to reevaluate the lower Permian (P 1) source rocks. The carbonate rocks in Maokou Formation (P 1 m) whose high organic carbon values were caused by external asphalt have poor hydrocarbon generation ability, but the argillaceous rocks in P 1 m have some, especially the recent discovered black shale in Gufeng deep-water facies in the north have good hydrocarbon generation ability. The black shale is 5–20 m thick and the measured average value of organic carbon can reach up to 7.24 wt%, which can greatly increase the hydrocarbon generation capacity in the north; The studies of natural gas sources of the lower Permian in eastern Sichuan basin show that the contribution of gas source is mainly Silurian. In the north, the lower Permian source rock is supplemented, while in the south, it's greatly affected by the coal-measure source rocks of Longtan Formation (P 2 l); Take the Wutan-1 well in Tanmuchang as an example to dissect the reservoir in syncline area. The Wutan-1 well has a tested daily production of more than 80 × 104 m3, and the paleotectonic evolution history shows that it was in the high position of the structure during the generation and expulsion peak of hydrocarbon. The fracture-vuggy lithologic reservoir of Wutan-1 well is favorable for hydrocarbon capture and later preservation. According to the above, the Tanmuchang syncline has a good spatio-temporal matching relationship, which is the key to hydrocarbon accumulation and exploration. This knowledge has expanded the exploration area of the Lower Permian Maokou Formation in eastern Sichuan, and more importantly, it brings much enlightenment to the exploration of the syncline areas in Sichuan basin and other basins at home and abroad. • The original nature of organic matters is introduced for the first time to reevaluate the lower Permian source rocks. • The black shale in Gufeng deep-water facies has hydrocarbon generation capacity in the north of the eastern Sichuan Basin. • The sources of natural gas in Maokou Formation are different between the north and the south in the eastern Sichuan Basin. • The syncline area of the Lower Permian Maokou Formation in eastern Sichuan has the potential for gas accumulation. [ABSTRACT FROM AUTHOR]