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Gravity flow deposits are important hydrocarbon reservoirs in deep lacustrine deposits. Previous studies have paid much attention to the hydrocarbon reservoirs in those intrabasinal classic turbidite deposits. However, relatively little is known about the distribution of oil reservoirs in those extrabasinal hyperpycnal flow deposits. With the help of cores and wireline logging data, the present study undertakes a description and interpretation of subsurface shale oil reservoirs in the deep lake deposits in Chang 7 member, Yanchang Formation, Ordos Basin. Parallel bedded fine sandstone (Sh), massive bedded fine sandstone (Sm), massive bedded fine sandstone with mud clasts (Smg), deformed bedded siltstone (Fd), wave-lenticular bedded siltstone (Fh) and black shale (M) were found and interpreted in those deep lake deposits. The deposits were interpreted as hyperpycnal flow deposits which developed in channel, levee and deep lacustrine facies. The development of the Chang 7 sand body increased gradually, and the sand body of Chang 71 was found to be the main position of sandy hyperpycnites. The fine description of the sand body indicated a channelized sedimentary pattern. The thick sandy hyperpycnites mainly developed in the middle of those channels, and the eastern part of the study area was found to be the main deposition position of the hyperpycnal flow deposits. From the perspective of plane overlap and single well analysis, a thick sand body is the favorable position for the development of an oil reservoir, which has a significant control effect on the reservoir scale and oil production. This research can aid in understanding the facies distribution of hyperpycnal flows and has implications for hydrocarbon reservoir exploration. [ABSTRACT FROM AUTHOR]

Forty-six crude oil samples were selected from the Ordovician in the northwestern part of the Tahe oilfield for detailed molecular geochemical and isotopic analysis, including group compositions, carbon-hydrogen isotopes and gas chromatograms of saturated hydrocarbons, as well as the characteristics of terpane, sterane and other biomarkers, indicating that crude oils are of the same origin from different districts in the Tahe oilfield and were derived from the same source kitchen (or oil source formation), i.e., mainly stemming from marine hydrocarbons. Detailed studies of oil physical properties of 25-honpane revealed that such oils have heavy or thick oil qualities due to biodegradation. Comprehensive assessment in terms of five maturity parameters shows that the oils from the Ordovician with R values varying from 0.80% to 1.59% are widely distributed in the northwest of the Tahe oilfield. [ABSTRACT FROM AUTHOR]

In the future time the exploration of marine oil and gas will be one of the significant domains in China. In this paper the biomarker assemblage characteristics of oilshow in the Nanlinghu Formation of the Majiashan profile, which is located in Chaoxian County, south of Anhui Province, are described in the light of gas chromatography/mass spectrometric (GCMS) analysis on the qualitative and quantitative basis. Based on the investigation of the biomarker assemblage characteristics of possible source rocks developed in the area studied, a conclusion is drawn that the oilshow was generated from the Nanlinghu Formation source rocks (abbreviated as T1 n), instead of the Qixia Formation source rocks (abbreviated as P1 q). It is pointed out that the T1 n is of strong potential for future oil exploration, and therefore much attention should be paid to it. [ABSTRACT FROM AUTHOR]

• The cherts in the slope and basin setting were strongly affected by hydrothermal activities. • The oxygen isotope value of paleo-seawater was assessed during the early Cambrian. • The paleo-seawater temperature presented an obvious gradient trend in South China. • There existed an oxygen minimum zone (OMZ) during the shelf and slope transition. • Biological reproduction was closely related to seawater temperature and oxic environment. The Ediacaran–Cambrian transition period was a critical time interval for the environmental fluctuations and organismal evolution in geological history, popularly known as the "Cambrian Explosion". The diagenetic mechanism of the widely developed Liuchapo bedded cherts in South China remain unclear and controversial during this critical time interval. To address this, we examined silicon and oxygen isotopes, as well as major and trace elements in the Liuchapo cherts from three wells developed from slope to basin facies in South China. Results reveal that the bedded cherts from the three wells were affected by episodic hydrothermal activity, and the percentage of hydrothermal fluids is highest in the Xc1 well and lowest in the Xb1 well. The paleo-seawater temperature, calculated from chert oxygen isotope values, present a gradual increasing trend from shallow- to deep- areas in South China from 542 to 526 Ma. Redox proxies indicate that the water column of the Xa1 and Xc1 wells were dominated by suboxic condition, while those of the Xb1 well was mainly in oxic conditions. There should exist an oxygen minimum zone (OMZ) during the shelf and slope transition. A suitable temperature and oxic environment are conducive to biological reproduction, which is consistent with higher primary productivity and abundant acritarch fossils in the Xb1 well. Silicon isotope values range from −0.6 ‰ to 1.2 ‰ in the three wells. The diagenetic origin of the Xa1, Xb1, and Xc1 wells was the consequence of the mixture of hydrothermal fluid and seawater, biological activity, and direct hydrothermal precipitation, respectively. Due to the redox condition and seawater temperature variation, silica-secreting organisms should be relatively limited. The episodic hydrothermal fluid, biological activity, and replacement of precursor rock may jointly affect the formation of the Liuchapo bedded cherts during the Ediacaran–Cambrian transition. [ABSTRACT FROM AUTHOR]

The occurrence and enrichment of shale plays are highly controlled by pore characteristics of the formation. In this study, an immature sample rich in kerogen type III from the Damoguaihe formation, Hailar Basin in China is subjected to hydrous and anhydrous pyrolysis (HP and AHP) across an extensive temperature range (300–450 °C). Next, low-pressure N 2 adsorption analysis was conducted on the pyrolyzate of each maturity stage to study the pore structures' evolution during thermal maturity simulation. Moreover, deconvolution and fractal dimension analyses were implemented to study pore families and the complexity of pores within the shale samples. Finally, radial basis function (RBF) neural networks optimized by four evolutionary approaches were applied for modeling N 2 adsorption data obtained from the HP and AHP samples. According to the results, the original shale sample and all pyrolyzates obtained with HP and AHP scenarios exhibited type IV isotherm with H3 hysteresis loops. As a whole, BET surface area, micro-, meso- and total pore volume of HP pyrolyzates were higher than AHP ones. The unheated shale sample had seven families containing three mesopore and four macropore groups. Although all pyrolyzates obtained from the pyrolysis had families with similar means, their pore volumes were entirely different, which proves that the pore structure of samples undergoes changes during thermal maturation and the presence of water can also enforce these changes. Both fractal dimensions showed a direct relationship with BET surface area and a negative correlation with the average pore diameter of shale samples. The RBF model optimized by differential evolution (DE) delivered a mean absolute percent relative error (MAPRE) value of 4.84% and determination coefficient (R2) of 0.9946 for the total data set, which outperforms other RBF models in predicting N 2 adsorption/desorption tests of pyrolyzates. The outcome of sensitivity analysis suggested that the N 2 adsorption/desorption behavior of the pyrolyzates was mostly affected by relative pressure and the pyrolysis type (HP or AHP). Ultimately, the results clearly revealed that the effect of water on the pores' alteration of shales with type III kerogen is greater than the effect of temperature or thermal maturity itself. • An immature kerogen type III sample from Damoguaihe formation is subjected to HP and AHP tests. • Original and all artificially matured samples exhibited type IV isotherm with H3 hysteresis loops. • BET surface area, micro-, meso- and total PV of HP samples were higher than AHP ones. • The RBF AI model optimized by DE outperformed other RBF models in predicting N 2 adsorption/desorption. • N 2 adsorption/desorption is affected by relative pressure and pyrolysis pathway, the most, among all parameters. [ABSTRACT FROM AUTHOR]

It is widely accepted that significant perturbations in ocean redox states are closely related to biological evolution during the early Cambrian. However, the host and geochemical cycle of redox-sensitive elements (V and Zn) of the Niutitang Formation shale in South China have not been well-constrained. This study reports lithofacies, mineralogy and geochemical data of high-resolution samples from slope and basin settings (Xa1 and Xb1 wells, Hunan Province), to evaluate the significance of redox condition and hydrothermal contribution to trace element accumulation during the early Cambrian. Our results reveal the Zn-rich host is primarily sphalerite, while the V-rich host includes organic matter, illite, and anatase minerals in the Niutitang shale. Illite and anatase minerals have significant V concentration (14.8% and 18.3%), whereas organic matter contains relatively lower V concentration (1.4%). Trace elements can be scavenged by dissolved organic matter in seawater, and then taken up by clay minerals or form sulfide during deposition/diagenesis of organic-rich shales. Although seawater restriction of the lower member (LM) shale was stronger than in the upper member (UM) shale, euxinic conditions were more conducive to V and Zn enrichment than ferruginous conditions. Specifically, dwindling concentrations of V and Zn in seawater existed in South China during deposition of the early LM shale. However, the ocean experienced episodic hydrothermal activity, which may have supplied abundant trace elements to supplement seawater content. Overall, we propose that the V and Zn geochemical cycles in the early Cambrian paleo-ocean were controlled by redox condition, organic matter, and the trace element inventory of seawater. • The hosts of V and Zn elements in organic-rich shale of Niutitang Formation have been determined. • Euxinic condition was more favorable for the enrichment of trace elements relative to ferruginous condition. • The seawater restriction of UM/LM shale of Niutitang Formation was investigated. • V and Zn inventory in the ocean was in a drawdown trend during the early Cambrian. • Hydrothermal activity may carry abundant trace elements into the ocean. [ABSTRACT FROM AUTHOR]

The central Junggar Basin in western China is unique because it provides insights into the geochemistry of oil from Jurassic coal measures. The analysis of TOC, Rock-Eval pyrolysis, gas chromatography-mass spectrometry (GC-MS), and carbon isotopes was performed to characterize the oil geochemistry and evaluate the hydrocarbon generation potential of source rocks in a coal-bearing formation. Fluid inclusions, fluorescence microscopy, and burial-thermal history were also used to study the oil generation and charging histories. The results show that the mudstone of the Badaowan Formation is the main source rock of the Jurassic and has relatively high hydrocarbon generation potential. The Jurassic oil in the Zhong-4 Block is moderately mature, with an equivalent Ro of about 0.75%. The oil is characterized by heavy carbon isotopes, a predominance of Pr over the Ph, low abundances of trisnorhopane (Ts), tricyclic terpanes and gammacerane, predominance of C 29 steranes among regular steranes, a preponderance of naphthalene and its alkylated analogues in aromatic compounds, and abundant polycyclic compounds. Such geochemical data indicate a contribution of Jurassic humic type organic matter to the oil. The mudstone in the Badaowan Formation started generating hydrocarbons in the Early Cretaceous and reached the peak of hydrocarbon generation in the middle Cretaceous. One major hydrocarbon charging episode is suggested in the Late Cretaceous and another in the early Neogene. The Fukang Depression in the south is the source kitchen, and oil migrates in a direction of southwest to northeast through faults and sandstone carrier beds. • The Jurassic mudstones and oils are mostly within the oil window. • The mudstone in Badaowan Formation is the primary Jurassic source rock. • Unique biomarker characteristics of the Jurassic oil are demonstrated. • The Jurassic oil shows heavy carbon isotopes (δ 13 C > -28‰). • Two major hydrocarbon charging periods for the Jurassic reservoirs are suggested. [ABSTRACT FROM AUTHOR]

Evaluating pore structure of unconventional shale reservoirs enables us to determine their productivity, allowing for better operational decisions. Despite extensive studies in this field, considering the complexity of shale plays, pore structure analysis of such formations still requires novelties and further research. In this study, 10 samples from the Qingshankou Formation (from 5 wells) were analyzed with X-ray diffraction (XRD), programmed pyrolysis, N 2 adsorption, and mercury intrusion capillary pressure (MICP). In the next step, several modern intelligent smart models including multilayer perceptron (MLP), radial basis function (RBF), generalized regression neural network (GRNN), cascaded forward neural network (CFNN), and least squares support vector machine (LSSVM), that were optimized by levenberg-marquardt (LM), Bayesian regularization (BR), genetic algorithm (GA), ant colony optimization (ACO), particle swarm optimization (PSO), and differential evolution (DE) algorithms were employed, to estimate the volumes of N 2 adsorbed and desorbed based on the mineralogy and geochemical properties of the samples. Results show that samples are mainly composed of clay (up to 42.3 wt%) and quartz (up to 34.6 wt%), low in total organic carbon (TOC) (up to 2.89%) and in the oil generation window. Complexity of smaller pores was found higher compared to medium and larger ones. In addition, deconvolution of N 2 adsorption pore size distribution (PSD) curve revealed that samples are composed of up to three families in the range of macropore size and different families in mesopore size. We found that LSSVM with applicability to the entire input dataset, outperformed all other models in predicting the amount of nitrogen adsorption and desorption with an average absolute percent relative error (AAPRE) value of 1.94%. Ultimately, clay minerals and potash feldspar had the greatest effect on increasing and decreasing the amount of nitrogen adsorbed and desorbed, respectively. The Leverage technique's findings demonstrate that more than 97% of total data points in the LSSVM model are in the valid domain. This study proves that smart methods if used properly, would enable us to study a large group of samples independent from exhaustive, time consuming and expensive experimental methods. [ABSTRACT FROM AUTHOR]

Pore structure plays an important role in controlling the oil migration and accumulation mechanism of subaqueous volcanic rocks (SVRs). The Santanghu Basin in western China is a unique region for providing insight into the pore structure characteristics of SVRs; however, little attention has been given to them. Thin-section analysis, scanning electron microscopy, low-temperature nitrogen adsorption (LTNA), pressure-controlled porosimetry, and nuclear magnetic resonance (NMR) experiments are performed on SVRs in the Santanghu Basin to reveal their pore structure characteristics and pore development patterns. The results show that the SVRs are dominated by ink bottle-shaped pores and have the characteristics of rather low matrix permeabilities (the Swanson parameters are mainly <4.0%/MPa), fine pore throats (r apex mainly <0.5 μm) and high capillary pressures (P 50 > 14.0 MPa). An effective method, namely, integrating NMR and LTNA experiments, is proposed to estimate the full-range pore size distribution (PSD) of the SVRs. In the full-range PSD, three peaks are identified at pore sizes of <1 μm, 1–10 μm and >10 μm, mainly corresponding to intercrystalline pores (IPs), dissolved pores (DPs), and residual vesicles (RVs), respectively. The storage space of SVRs is dominated by IPs, while the contents of DPs and RVs are the key to SVRs becoming effective reservoirs. The content of RVs is mainly controlled by the depth of the water body during deposition and the distance from the volcanic strata boundary. The higher the content of K and Na in the original composition and the closer the distance to the source rock is, the higher the proportion of DPs. In accordance with the original composition and the depth of the water body during deposition, the SVRs are divided into four types. Moreover, we propose the pore development patterns of the four types of volcanic rocks. RVs mainly exist in type I and type II SVRs, while DPs are important storage spaces in type I and type III SVRs. Finally, type IV SVRs only develop IPs and a few nanoscale DPs. • This paper characterized the pore development characteristics of SVRs in detail. • Pore development in SVRs depends on the depth of the water body during deposition and the original composition. • Division of four types of SVRs based on the formation environment and original composition. • Various types of SVRs show distinct differences in pore development pattern. [ABSTRACT FROM AUTHOR]