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In recent years, tight oil exploration has made significant progress in the lower part of Shahejie Formation ( Es 3 L ) in the Shulu Sag, Bohai Bay Basin, Eastern China, which shows good exploration prospects for tight oil. However, accurate evaluation of tight oil resource potential is influenced by a lack of studies and an incomplete understanding of hydrocarbon expulsion from marlstone source rocks. This study investigated the geological and geochemical characteristics of marlstone source rocks, their hydrocarbon generation and expulsion, and the tight oil resource. Results show that the marlstone source rocks were deposited in a reducing to weakly oxidizing lacustrine environment with low-middle salinity, distributed widely in the central and southern troughs, with the maximum thickness greater than 700 m. The marlstone source rocks have relatively high organic matter abundance (0.06–7.97% of total organic carbon content with an average value of 1.51%), are dominated by type II and I kerogen, and are at the immature to mature stage (0.3% < vitrinite reflectance (VR) < 0.8%), which reveals fair–good source rocks for the marlstones. The threshold and peak of hydrocarbon expulsion for marlstone source rocks are at 0.51% VR and 0.6% VR, respectively. The amounts of generation and expulsion from marlstone source rocks are 19.72 × 108 t and 8.53 × 108 t, respectively, with an expulsion efficiency of 43%. The total tight oil resource in place is 10.9 × 108 (5.8 × 108 t within the carbonate rudstone reservoir and 5.1 × 108 t within the marlstone reservoir), indicating a significant tight oil potential and promising exploration prospect in the Shulu Sag, Bohai Bay Basin, Eastern China. [ABSTRACT FROM AUTHOR]

In recent years, there has been significant progress in shale oil exploration in the first member of the Qingshankou Formation (K2qn1) in the Qijia‐Gulong Sag, Songliao Basin, Northeast China: It shows good prospects for shale oil. However, the recognized lack of the geochemical and hydrocarbon generation and expulsion characteristics of K2qn1 source rocks limits an accurate evaluation of shale oil resource. This study systematically investigated the geological and geochemical characteristics, hydrocarbon generation and expulsion, and shale oil potential of the K2qn1 source rocks. The results show that the K2qn1 mudstones were mainly deposited in the semideep and deep lacustrine facies under reducing and weak reducing conditions. Compared with the southern Gulong Sag, the northern Qijia Sag has a higher salinity, more abundant prosperous aquatic organisms, and a greater paleoproductivity. The K2qn1 source rocks are pervasive and continuous in the entire sag, with maximum thicknesses greater than 110 m. They have a higher organic matter (OM) abundance (2.40% of the average TOC), are dominated by type I and II1 kerogen, and are mature (0.8%‐0.1.3% VR), which indicate that they are good to excellent source rocks and have significant hydrocarbon generation potential. The source rocks in the Qijia Sag have a higher OM abundance, a better OM type, and a lower OM maturity than those in the Gulong Sag. The threshold and peak hydrocarbon expulsion values for marlstone source rocks are 0.85% VR and 0.95% VR, respectively. The volumes of hydrocarbons generated and expulsed from the K2qn1 source rocks are 121.8 × 108 t and 46.9 × 108 t, respectively, with a retention efficiency of 61.5%. The in‐place and recoverable resources of shale oil are 74.9 × 108 t and (12.0‐13.5) × 108 t, respectively, indicating that the entire sag has a significant shale oil potential, especially the Qijia Sag. [ABSTRACT FROM AUTHOR]

We documented a new type of self-sourced unconventional reservoir consisting of interbedded organic-rich marlstone and calcareous conglomerates developed in lacustrine carbonate successions in the Eogene Shahejie formation (Es 3 3 ) of Shulu Sag, Bohai Bay Basin. The Es 3 3 interval used to be regarded as a set of homogeneous source rock for oil plays in the upper strata due to their high abundance of organic-matter. However, the Es 3 3 interval actually has very strong heterogeneity in their organic richness and hydrocarbon generation ability among different stratigraphic sequences (the Es 3 3 interval can be divided into sequence SQ1 to SQ5 from bottom to up). To better understand the heterogeneity in the unconventional reservoir and its effect on the hydrocarbon retention and migration, thin sections and scanning electronic microscopes were used to characterize the pore system in the reservoir, together with a amount of collected well database including wireline logging, gas logging, and physical property data (e.g. porosity and permeability). Intensive sampling from the Es 3 3 interval of Well ST1H was performed and samples were measured with Rock-Eval and TOC analysis. The rock extracts were analyzed with SARA and gas chromatography - Mass spectrum (GC-MS) analysis to examine the fluid geochemical characteristics and molecular biomarkers composition. The results show that although the whole Es 3 3 are characterized by low and ultra-low porosity and permeability, but the pore types in different lithology are different. The organic-rich marlstones develop large amount of organic matter pore and dissolved mineral pores, while the conglomerates developed inter-partical or inter-crystalline mineral pores dominantly. The sequence SQ2 has high quality of source rock for hydrocarbon generation, possessing moderate to high content of organic matter (TOC range 2–5 wt %) with Type I-II kerogen predominantly, basically in the thermal maturity stage of the peak oil window. OM and lithology play significant roles in controlling hydrocarbon expulsion and retention. Oil retained in the organic-rich marlstone was observed to absorb on the surface of OM and clay-rich matrix, which is also supported by the positive correlation between retained oil (represented by Rock-Eval S1) and TOC. Organic-lean conglomerates in the sequence SQ3 obtain abnormal high content of low mature oil determined by biomarker composition, which suggests the oil were derived from oil migration and mixture. Thermal maturity profile based on hydrocarbon biomarkers composition of rock extract provides a method to determine the effect of the hydrocarbon migration or retention within source rock. The organic-lean intervals adjacent or close to organic-rich source rock can be favorable targets for oil exploration. [ABSTRACT FROM AUTHOR]

Different from previous studies on effect of weathering upon geochemical variation along a single weathered profile, this paper provides a new methodology validated by comparing a weathered outcrop samples and their stratigraphic counterpart un-weathered core samples in a nearby shallow borehole. This outcrop and borehole penetrated the Ordovician-Silurian Wufeng–Longmaxi shales, located in the same anticline structure in the northern part of Guizhou Province, Southern China. The mineral composition, major, trace and rare earth elements (REEs) composition and Rock-Eval parameters of outcrop and core samples were analyzed and compared. Organic matter (OM) was observed in the microscope and extracted for elements analysis. The results show that short-term weathering still has significant influence on OM, mineral and elemental composition of black shales. The elements composition shows the outcrop profile was moderately weathered. The REEs compositions do not alter much during weathering process and the REEs composition and their relative ratios still are valid for rock origin determination. The OM, mainly composed by graptolite and bitumen, even entering the highly-over thermal maturity, is still sensitive to the weathering with a systematic loss 30–50% of TOC along the outcrop profile, which suggests that the OM consumption is predominantly controlled by weathering duration and the distance from the weathering surface. In turn, OM has significant influence on the trace elements transportation behavior during weathering. Some trace elements associated with the OM such as V, Cr, Th, U, Ni and Co, change significantly in their absolute concentration during weathering, but their relative ratios do not necessarily change too much and might be still reliable proxies for paleo-environmental determination. The mobility of shale minerals during weathering is in the following order: plagioclase > potassium feldspar and dolomite >pyrite and OM. Short-term weathering can also result in considerable transportation of elements and significant variation of minerals content in black shale, which may pose potentially high environmental and engineering risk in the regions rich in black shale. [ABSTRACT FROM AUTHOR]

With the purpose of characterizing the organic geochemistry and investigating the shale gas potential, we applied multiple methods, including quantifying organic matter richness, polarizing microscope observations, maceral composition analysis, kerogen stable carbon isotope analysis, vitrinite reflectance analysis, and Rock-Eval pyrolysis were performed on black shale samples from the Lower Permian Shanxi and Taiyuan formations in the Mouye-1 well of the Southern North China Basin. The results indicate that the average total organic carbon (TOC pd ) content at the present time is 1.73% and 2.41% for Shanxi and Taiyuan shale samples, respectively. The microscopic distribution of organic matter includes scattered types and local enrichment types, as well as layered enrichment types. These types were revealed by polarizing microscope observations and exhibit an excellent correlation with the TOC content of shale samples. Based on maceral compositions and kerogen stable carbon isotopes, organic matter in Shanxi and Taiyuan shales is characterized by gas-prone, inertinite-dominated type III kerogen. The thermal maturity, as indicated by measuring vitrinite reflectance (3.2–3.6%R o ), suggests that shale samples from Shanxi and Taiyuan formation in the Mouye-1 well have evolved far into the metagenesis stage, and no significant amounts of hydrocarbons can be generated. The remaining hydrocarbon generative potential, S2 (0.02–0.77 mg HC/g Rock), which was determined by Rock-Eval pyrolysis, also supports this conclusion. Additionally, the original total organic carbon (TOC o ) content and hydrocarbon generative potential (S2 o ) were reconstructed based on Jarvie's equations for these thermally over-mature shales; this reconstruction indicated poor to fair original source rock potentials based on the correlations of TOC o and S2 o . Furthermore, the total volume of gas generated during thermal maturation was calculated using a conversion formula based on molar mass and resulted in a yield of 5.69 cm 3 /g Rock and 3.54 cm 3 /g Rock for Shanxi and Taiyuan shale samples, respectively. Overall, inertinite-dominated maceral compositions of kerogen with extremely high thermal maturity can have a negative effect on the gas potential of shale in the Southern North China Basin. [ABSTRACT FROM AUTHOR]

The Datang Formation black rock series deposited in an inter-platform basin are considered to be one of the main source rocks in Southwest China. However, their depositional conditions and organic matter enrichment in such a setting are not well understood. In this study, geochemical characteristics of total organic carbon (TOC), major, trace and rare earth elements (REEs) of thirty black rock series samples from a newly-cut roadside outcrop (Zhenning section) in Southern Guizhou, Southwest China are systematically investigated to examine provenance, paleoredox conditions, paleoclimate, paleoproductivity and sedimentary rate, and further to explore their influence on organic matter enrichment. Results show that TOC contents of the investigated samples range from 0.90% to 2.83%, with an average of 1.45%, with TOC variations being in accord with the stratigraphic cyclicity. These data also indicate that the target black rock series were deposited in a combination of continental island arc and active continental margin tectonic setting that exhibited moderate weathering, oxic/dysoxic oxygen levels, hot and arid to semiarid climate, and a higher sedimentary rate. Multiple paleoredox indicators (e.g., Ni/Co, V/Cr, U/Th and V/(V + Ni) ratios), together with slightly negative Ce anomalies and EFU-EFMo covariation, totally suggest an oxic/dysoxic water environment, which is usually considered unfavorable for organic matter preservation. Average (La/Yb)N ratios (1.41) reflect a higher sedimentary rate, resulting in shortening the exposure time of organic matter in the degradation region of aerobic bacteria under oxic/dysoxic conditions. Of the three factors that could affect organic matter enrichment, including paleoproductivity, paleoredox conditions and sedimentary rate, the relatively high paleoproductivity indicated by the relatively high TOC contents appears to be the dominant factor. In contrast, the other two factors, i.e., paleoredox conditions and the rate of sedimentation play relatively less significant roles. Based on these factors, an enrichment model of organic matter for the black rock series in Southern Guizhou Depression is established. These findings also contribute to constraining the sedimentary environment in such a setting and further deepen our understanding of the potential shale gas resources of the Southern Guizhou Province. [ABSTRACT FROM AUTHOR]

The article discusses a research concerning the formation and evolution mechanism of tight oil and gas in lacustrine carbonate rocks in the Bohai Bay basin in China. Topics include the distribution of lacustrine carbonate rocks in the Bohai Bay basin, thermal evolution of organic matter in source rock, and retained hydrocarbon and its composition in source rocks. The four stages of the formation process of tight oil are noted.

Shale samples collected from seven wells in the southeastern Ordos Basin were tested to investigate quantitatively the pore structure and fractal characteristics of the Lower Permian Shanxi Shale, which was deposited in a marine-continental transitional (hereinafter referred to as the transitional) environment. Low-pressure nitrogen adsorption data show that the Shanxi Shale exhibits considerably much lower surface area (SA) and pore volume (PV) in the range of 0.6–1.3 m 2 /g and 0.25–0.9 ml/100 g, respectively. Type III kerogen abundant in the transitional Shanxi Shale were observed to be poorly developed in the organic pores in spite of being highly mature, which resulted in a small contribution of organic matter (OM) to the SA and PV. Instead, I/S (illite-smectite mixed clay) together with illite jointly contributed mostly to the SA and PV as a result of the large amount of inter-layer pores associated with them, which were evident in broad-ion-beam (BIB) imaging and statistical analysis. Additionally, the Shanxi Shale has fractal geometries of both pore surface and pore structure, with the pore surface fractal dimension (D1) ranging from 2.16 to 2.42 and the pore structure fractal dimension (D2) ranging from 2.49 to 2.68, respectively. The D1 values denote a pore surface irregularity increase with an increase in I/S and illite content attributed to their more irregular pore surface compared with other mineralogical compositions and OM. The fractal dimension D2 characterizing the pore structure complexity is closely related to the pore arrangement and connectivity, and I/S and illite decrease the D2 when their contents increase due to the incremental ordering degree and connectivity of I/S- or illite-hosted pores. Meanwhile, other shale constituents (including kaolinite, chlorite, and OM) that possess few pores can significantly increase the pore structure complexity by way of pore-blocking. [ABSTRACT FROM AUTHOR]

To clarify the size distribution of different types of shale pores, nine Sinian–Cambrian shale samples from South China were examined using ion-milling, FE-SEM, nitrogen adsorption and mercury intrusion. Image-based point counting data indicated that nanopores are predominant, whereas pores larger than 1 μm are absent. Organic matter-hosted pores dominate below 130 nm, whereas intraparticle pores within carbonate, probably caused by dissolution, constitute most pores larger than 400 nm. The small amount of residual intraparticle and interparticle pores associated with rigid minerals mostly range from 50 nm to 250 nm. A positive relationship was found between the TOC and total pore volume measured by nitrogen and mercury. The mercury volume of pores larger than ~ 300 nm increased with increasing dolomite and decreasing clay mineral content. The statistics from image-analysis and the relationship between pore volume and shale components were in good agreement, indicating that different types of pores have their own relative restricted size range. Generally, intraP pores are larger than pores associated with rigid minerals, whereas the OM pores and interP pores associated with OM or clay are the smallest. Through a comparison with other less matured shale formations, the highly matured (equivalent vitrinite reflectance above 3%) Sinian–Cambrian shale in South China was characterized in this study as those with smaller interP pores, which is probably due to a stronger compacting effect. [ABSTRACT FROM AUTHOR]

Abstract: The Songhua River is one of the biggest rivers in China and is the major freshwater source for industry and agriculture, as well as the source of the drinking water for millions of residents living along it. Heavy contamination of the Songhua River is due to domestic sewage and industrial wastewater. Thus, we set out to determine the carcinogenic potential of water samples taken from drinking water source of Harbin city in the Songhua River. Short-term genotoxic bioassays using Ames, SCE, and cell transformation assays were employed to examine the genotoxic activity of the ether extracts of water samples taken from the Songhua River. The results of the Ames test indicated that there were frame shift mutagens in the water samples, which were both direct and indirect. A dose–response relationship for the SCE assay was obtained, and the SCE cumulative frequency moved obviously to the right with increasing doses of water samples. Typical transformed foci were formed in NIH3T3 cells induced by ether extracts of water samples and the transformation frequency showed a dose–response relationship. The transformed cells showed the characteristics of malignant cells. All of the results indicated that the ether extracts of water samples taken from the Songhua River showed genotoxic activity. [Copyright &y& Elsevier]

[Display omitted] • Organic matter controls micropore volume without influence on porosity, while thermal maturity positively affects porosity. • I/S influences 20–50 nm pores, chlorite and kaolinite affect 2–5 nm pores, while illite positively contributes to all mesopores. • This study shows three types of mineral transformation, smectite-illite, smectite-illite-chlorite, and anorthite/albite-to-kaolinite/illite, in the early mature lacustrine shale. • Chlorite affects macropore volume, porosity, and pore throat radius. Pores related to organic matter and clay minerals provide significant storage space for hydrocarbons in organic-rich shales. However, the pore structure evolution and its related influencing factors at the early oil window stage are unclear. This study attempts to reveal the controls of organic matter and clay minerals on the pore structure of the lacustrine organic-rich Chang 7 Shale by using thin-section observational, organic petrological, elemental, scanning electron microscopy/Energy Dispersive Spectrometer (SEM/EDS) analyses, and mineralogical analyses combined with the pore structure characterization of gas adsorption and mercury injection capillary pressure (MICP). The results show that micropores (less than 2nm) and mesopores (2–50 nm) contribute to the main storage space in organic-rich intervals of the Chang 7 Shale. Organic matter content controls the development of micro-pores while no effects on porosity in the early mature lacustrine shale. Shrinkage OM pores related to the expulsion of hydrocarbons are better developed than the complex pores and sponge pores. Total clay content is correlated with mesopores volume in organic-rich lacustrine shale. Multiple stepwise linear regression model between mesopores volume and different clay minerals shows that the pores with diameters in the ranges of 2–5 nm are controlled by illite, chlorite, and kaolinite, and the pores with diameters in the ranges of 5–10 nm and 10–20 nm are controlled by illite, while 20–50 nm pores rely on illite/smectite mixed layer (I/S) and illite. Thermal maturity shows a positive effect on pore volume and porosity. There are three types of transformations of clay minerals in lacustrine shale, including the smectite-illite conversion, smectite-illite-chlorite conversion, and anorthite/albite-to-kaolinite/illite conversion. These clay mineral conversions all show positive effects on pore volume, especially the anorthite/albite-to-kaolinite/illite conversion, while the smectite-illite conversion shows some negative effects on the connectivity of the pore system. Additionally, the control of macropore volume, porosity, and pore throat radius by chlorite cannot be ignored. The findings from this study contribute to a clear insight into the pore structure evolution of lacustrine shale. [ABSTRACT FROM AUTHOR]