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The heterogeneity, sedimentary characteristics, and distribution of fine-grained sediments of millimeter-scale laminae were studied in alkaline lacustrine strata in the lower Permian Fengcheng Formation (P1f2) in the Mahu Sag to provide a sound theoretical basis for shale oil exploration and development. They were investigated by using core and thin-section observation, geochemical and elemental analysis, mineral identification, and pore examination. Five types of laminae were distinguished, with different mineral compositions, pore characteristics, and distributions. These laminae occur in four distinct combinations. The pore systems predominantly consist of intercrystalline pores, intragranular pores, and dissolution pores of feldspar and dolomite and also contain imporous alkaline mineral particles. Influenced by variations in salinity, the influx of volcanic–hydrothermal material, and the participation of both endogenous and exogenous materials, the formation has gone through five stages of sedimentary evolution. Furthermore, felsic laminae (FQL), dolomite laminae (DOL)/reedmergnerite laminae (RL)/shortite laminae (SL), and chert laminae (CL) developed in single-terrestrial-source still water deposition, hybrid-source still water deposition, and single-intrasource deposition, respectively. Vertically, the FQL-DOL combination shows favorable reservoir characteristics and is the most extensively developed lamina combination in the Fengcheng Formation that primarily developed in the period of the late Feng 1 Member (P1f1), the early Feng 2 Member (P1f2), the late Feng 2 Member (P1f2), and the early Feng 3 Member (P1f3). The FQL-RL/SL combination primarily developed in the period of the middle P1f2, and the DOL-CL combination is the counterpart in the period of the early P1f2 and the late P1f2 stages. Considering this in conjunction with the longitudinal distribution of lamina combinations, a model is proposed for the distribution of fine-grained sediments in alkaline lacustrine strata. [ABSTRACT FROM AUTHOR]

Mid-high maturity shale oil is the most realistic field for the scale breakthrough of terrestrial shale oil production in China. Generally, three deficiencies hinder shale oil development in China: heavy oil density, small sweet spot areas, and poor distribution continuity. Thus, identifying the "sweet spots" in shale oil reservoirs is critical for the efficient exploration and development of terrestrial shale oil. This study targets the siltstone type (Class-II shale oil) and pure shale type (Class-III shale oil) of the Chang 7 Member in the Ordos Basin, and identifies three stratigraphic units, namely the hydrocarbon accumulation unit, hydrocarbon generation unit, and hydrocarbon retention unit, which together constitute the in-source "shale oil system". The hydrocarbon accumulation unit is mainly siltstone, where the hydrocarbons are migrated from shales. It has favorable pore-throat network connectivity with a pore connectivity ratio of 32–57%, being the siltstone-type sweet spots. The hydrocarbon generation unit is mainly composed of high-TOC mudstone/shale and is the main contributor to in-source hydrocarbon generation and expulsion. This unit has high three-dimensional connectivity (28–30%), as shown by the pore-throat network model, associated with vertical paths for hydrocarbon expulsion. The hydrocarbon retention unit is mainly composed of low-TOC mudstone/shale retaining self-generated and migrated hydrocarbons. The pore connectivity rate is 17–42%, and the pore-throat network connectivity direction is uneven. Light and low-carbon-number hydrocarbons are preferentially trapped or even sealed in small pores of the retention unit, forming the typical mudstone/shale-type sweet spots. In the process called shale oil intra-source migration, the oil migrates in source rocks causing component fractionation, which allows more shale oil to enrich in the hydrocarbon accumulation and retention units to form sweet spots, compared with the hydrocarbon generation unit. The migration paths include the one from mudstone/shale to siltstone interlayers and that from the high-TOC mudstone/shale intervals to the low-TOC intervals. The in-source accumulation of shale oil shows the differentiated enrichment model featuring "high-TOC mudstone/shale generating hydrocarbons, low-TOC mudstone/shale retaining hydrocarbons, siltstone accumulating hydrocarbons and multiple intra-source migration paths". In the Ordos Basin, the organic-lean (TOC 1–3%) mudstone/shale intervals appear to be the sweet spots of shale oil, where there are abundant medium-short-chain hydrocarbons retained with high flowability. After fracturing stimulation, their production conditions may be even superior to those of siltstones. This proposed idea changes the previous strategy to look for sweet spots in high-TOC intervals derived from the shale gas industry. [ABSTRACT FROM AUTHOR]

"Sweet sections" in giant shale oil provinces are preferential fields that primarily support China to increase the reserves and production of continental shale oil. Based on the study of the geological conditions of shale oil in the continental basins in China, it was found that the shale stratum in major oil generation windows generally has higher degrees of oil and gas accumulation, and mostly contains oil. Hydrocarbon generation and reservoir capacities are the two key parameters for evaluating and optimizing favorable shale oil provinces. The evaluation index (volume of shale stratum multiplied by total organic carbon (TOC) multiplied by total porosity) for the giant continental shale oil provinces is also proposed. It is optimized that the Upper Triassic Chang 7 Member in the south-central Ordos Basin, Lower Cretaceous Qing 1 Member in the Gulong-Changling Sag in the Songliao Basin, Middle — Lower Permian in the Junggar Basin, Da'anzhai Member of the Ziliujing Formation of Lower Jurassic in the central and northern Sichuan Basin, and Paleogene oil-rich sag in the Bohai Bay Basin are the five giant continental shale oil provinces. The word "geological sweet sections" in continental shale oil provinces of China refers to favorable shale intervals which are relatively rich in oil, with superior physical properties, and more easily modified and developed commercially under applicable economic and technological conditions. After evaluation, there are mainly two types of "geological sweet sections" of giant continental shale oil developed onshore in China. One type of "geological sweet sections" is generally mudstone with optimal physical properties or a thin tight reservoir, to which the shale oil migrates a short distance. They are medium-to-high-mature zones with a thin sandy shale stratum in the Chang 7 Member in the Ordos Basin, mixed shale stratum in the medium-mature Lucaogou Formation in the Jimsar Sag, and multi-layered mixed Paleogene shale stratum in the Bohai Bay Basin. The other type of "geological sweet sections" is generally shale oil residing in various shale reservoir spaces. This type was developed in the Qing 1 Member in the Gulong Sag and Da'anzhai Member in the north-central Sichuan Basin. Free shale oil mainly occurs in shale, sandy-carbonate lamina, micro-lamella structure, and micro-fractures. Layers with lamina, lamination, and micro-fractures are generally shale oil "geological sweet sections." Starting from field tests and the construction of the "geological sweet sections" in giant continental shale oil provinces, the shale oil industry has been rapidly developing and will become an important supplement to domestic oil production in China. [ABSTRACT FROM AUTHOR]

Artificial ecological corridors (AECs) are internationally approved ecological restoration and climate mitigation strategies. The width and recovery time indices of AECs directly affect the restoration efficiency of degraded soil nutrients. However, there is a lack of comprehensive and quantitative evaluation research on the construction factors of AECs from the perspective of soil fertility improvement. This research aimed to examine the critical ecological corridor construction factors affecting Mollisols' eco-chemometrics and give a scientific scope. We collected 55 Mollisol samples at different restoration years (0–35 years) and different distances (0–280 m) from the AEC of the Ashi River, a typical Mollisol restoration area in Harbin, and the cold regions of China. We measured the distances, restoration years, soil thickness, pH, electrical conductivity (EC), cation exchange capacity (CEC), soil total organic carbon (SOC), soil total organic matter (SOM), dry matter content (DMC), and the proportion of nitrogen (TN), phosphorus (TP) and potassium (TK). The results are as follows: (1) Within the AEC, there were significant differences in soil stoichiometric characteristics in different restoration years and locations; after restoration for 10–35 years, the soil stoichiometric characteristics reach or exceed the reference value of Mollisols. (2) It is feasible to restore large-scale degraded Mollisols through ecological corridors. In this recovery process, the soil nutrients first decreased, then increased, and finally reached and exceeded the reference value of normal Mollisols. (3) Soil nutrient accumulation was related to ecological corridor width and recovery time. The recommended unilateral width of the ecological corridor based on Mollisols' CEC and SOC indices for restoration is 175–225 m, and the restoration period is 22.7–35 years based on Mollisols' EC and SOC indices for restoration. This study demonstrated the change mechanism of Mollisols in AECs based on recovery time and location, and provided the basis for the Chinese government to formulate policies for Mollisol remediation. [ABSTRACT FROM AUTHOR]

The organic-rich shale of the Qingshankou Formation (K2qn) is the most important target in the Songliao Basin. The relationship between lithofacies and source rock quality, however, is still controversial. Core observation, thin section identification, X-ray diffraction, organic geochemistry, and other analytical methods were adopted to investigate the petrology and its effects on hydrocarbon potential of the Qingshankou shale. Based on the differences in minerals, bioclastic, and fabric of laminae, four main lithofacies were defined as: (i) felsic shale (FS), (ii) clay shale (CS), (iii) bio-bearing shale (BS), and (iv) mixed shale (MS). The clay minerals content in the CS (average: 46.72 wt%) and MS (average: 41.11 wt%) was higher than that in FS (average: 39.97 wt%) and BS (average: 35.48 wt%). This classification allows the following comparative quantification of total organic carbon (TOC) content to be differentiated: CS > BS > MS > FS. Geochemical analysis indicated that the oil generation potential of the CS was the best, and the hydrocarbons generated from CS might migrate and accumulate in other lithofacies. All this knowledge could shed light on the lithofacies classification in shale systems with high clay mineral content, and may provide references for sweet spotting of the Qingshankou Formation in the Songliao Basin. [ABSTRACT FROM AUTHOR]

This study examines the characteristics and pore evolution of the Baikouquan conglomerate reservoir in the Mahu sag of the Junggar Basin from original sedimentation and diagenesis. Analysis is based on core observation, thin section, X-ray diffraction, cathodoluminescence and image analysis, and combined with physical property and well log data. The results show that conglomerate reservoir in the Baikouquan Formation can be divided into three lithofacies types: Type I is argillaceous filling conglomerate facies, in which cementation and dissolution are not developed, and the interstitial material is mainly argillaceous; Type II is tuffaceous filling in fine conglomerate facies, in which volcanic rock debris, illite and dissolution are developed; Type III is sandstone filling conglomerate facies, in which cementation and dissolution are developed. The reservoir undergoes complex diagenesis, and the diagenetic sequence is: compaction→early chlorite film→early calcite cementation→detritus, feldspar and tuffaceous dissolution→quartz secondary enlargement→late calcite cementation→oil invasion→forming illite. Quantitative study of pore evolution shows that dissolution and calcite cementation are relatively developed in lithofacies Type III, and that compaction has a great influence on lithofacies Type I and II. According to comprehensive evaluation of lithofacies, diagenesis and pore structure characteristics, the reservoir space type is mainly the dissolution pore. It is mainly primarily mainly composed of lithofacies Type III, thickness of the gravel body is more than 25 m, porosity is generally more than 12%, which represents favorable conditions for the distribution of favorable reservoir. [ABSTRACT FROM AUTHOR]

The microscopic pore structure of sand-conglomerate rocks plays a decisive role in its exploration and development of such reservoirs. Due to complex gravels-cements configurations and resultant high heterogeneity in sand-conglomerate rocks, the conventional fractal dimensions are inadequate to fully characterize the pore space. Based on the Pia Intermingled Fractal Units (IFU) model, this paper presents a new variable-ratio factor IFU model, which takes tortuosity and boundary layer thickness into consideration, to characterize the Triassic Karamay Formation conglomerate reservoirs in the Mahu region of the Junggar Basin, Northwest China. The modified model has a more powerful and flexible ability to simulate pore structures of porous media, and the simulation results are closer to the real conditions of pore space in low-porosity and low-permeability reservoirs than the conventional Pia IFU model. The geometric construction of the model is simplified to allow for an easing of computation. Porosity and spectral distribution of pore diameter, constructed using the modified model, are generally consistent with actual core data. Also, the model-computed permeability correlates well with experimental results, with a relative error of less than 15%. The modified IFU model performs well in quantitatively characterizing the heterogeneity of sand-conglomerate pore structures, and provides a methodology for the study of other similar types of heterogeneous reservoirs. [ABSTRACT FROM AUTHOR]

In recent years, significant progress in shale gas exploration has been achieved in the Upper Ordovician (Wufeng Formation)-Lower Silurian (Longmaxi Formation) shales in the Upper Yangtze area, South China. Although many studies have been carried out on the Upper Ordovician-Lower Silurian shales, the controlling factors causing organic matter accumulation of these shales remain controversial. This study uses trace-element geochemistry and sedimentological methods to evaluate terrigenous input, redox conditions and primary productivity to explore the mechanisms of organic matter accumulation. The variation of terrigenous fraction elements (Al, Th and Sc) concentrations reflect a mixed influence of sea-level change and weathering. The sea-level of the Upper Yangtze Sea went through two cycles of transgression to regression during the Ordovician-Silurian transition. The Linxiang Formation, Kuanyinchiao Bed and the upper part of Longmaxi Formation developed during the periods of regression, whereas the Wufeng Formation and the lower part of the Longmaxi Formation developed during the periods of transgression. The paleo-productivity indexes of TOC content, ratios of Ba/Al and P/Al, and redox conditions proxies of Mo concentration, ratios of U/Th and V/Cr generally display similar variation patterns with respect to the sea-level changes. High TOC contents and Ba/Al and P/Al ratios indicate the paleo-productivity was high on the sea surface, as shown by relatively good positive correlations between Th vs. TOC, and Sc vs. TOC. This indicates that the paleo-productivity was controlled by the nutrients input through weathering. The good positive correlations between redox conditions indexes (U/Th and V/Cr ratios) with TOC content reflects reductive preservation conditions (anoxic to euxinic), thus implying they were an important controlling factor for organic matter accumulation. Nevertheless, redox conditions were closely associated with sea level change and organic matter decomposition. Therefore, the sea-level change and weathering were the primary controlling factors for organic matter enrichment across the Ordovician to Silurian transition. [ABSTRACT FROM AUTHOR]

Sandy-conglomerate reservoir has gradually become a major target of oil and gas exploration. Complex diagenetic process and diagenetic fluid play a significant role in affecting reservoir heterogeneity. Carbonate cements form at various stages of the diagenesis process and record various geological fluid information. Recently, one-billion-ton sandy conglomerate oil field was exposed in Triassic Baikouquan Formation, Mahu sag, Junggar Basin. Therefore, an integrated study applying casting thin sections, cathodeluminescence, fluorescence, carbon and oxygen stable isotopes, electronic probe microanalysis and aqueous fluid inclusions measurements was performed in order to identify the types of carbonate mineral and its representative diagenetic environment and discuss the influences of different CO2 injections on reservoir quality. The main findings are as follows: The reservoir is mainly composed of 70.33% conglomerate and 16.06% coarse-grained sandstone. They are characterized by low compositional maturity and abundant lithic debris. Four types carbonate cements are identified according to the petrological and geochemical characteristics, including two types of Mn-rich calcite, ferroan calcite, siderite and dawsonite. They display an unusual broad spectrum of δ13C values (−54.99‰ to +8.8‰), suggesting both organic and inorganic CO2 injections. The δ13C values of siderite are close to 0, and its formation is related to meteoric water. The δ13C values of ferroan calcite and the occurrence of dawsonite indicate the trace of inorganic mantle-derived magmatic fluids. The δ13C values and trace elements of Mn-rich calcite record the information of hydrocarbon-bearing fluids. The fluid inclusions measurement data and reservoir properties and oil-test data show that the oil content of reservoir is not only affected by the formation time of different cements, but also by the relative content of dissolution and cementation. For these reservoirs altered by carbonate cements, it does not cause poor oil-bearing due to blockage of secondary minerals. [ABSTRACT FROM AUTHOR]

The Sichuan Basin is rich in shale oil and gas resources, with favorable geological conditions that the other shale reservoirs in China cannot match. Thus, the basin is an ideal option for fully "exploring petroleum inside source kitchen" with respect to onshore shale oil and gas in China. This paper analyzes the characteristics of shale oil and gas resources in the United States and China, and points out that maturity plays an important role in controlling shale oil and gas composition. US shale oil and gas exhibit high proportions of light hydrocarbon and wet gas, whereas Chinese marine and transitional shale gas is mainly dry gas and continental shale oil is generally heavy. A comprehensive geological study of shale oil and gas in the Sichuan Basin reveals findings with respect to the following three aspects. First, there are multiple sets of organic-rich shale reservoirs of three types in the basin, such as the Cambrian Qiongzhusi Formation and Ordovician Wufeng Formation-Silurian Longmaxi Formation marine shale, Permian Longtan Formation transitional shale, Triassic Xujiahe Formation lake-swamp shale, and Jurassic lacustrine shale. Marine shale gas enrichment is mainly controlled by four elements: Deep-water shelf facies, moderate thermal evolution, calcium-rich and silicon-rich rock association, and closed roof/floor. Second, the "sweet section" is generally characterized by high total organic carbon, high gas content, large porosity, high brittle minerals content, high formation pressure, and the presence of lamellation/bedding and natural microfractures. Moreover, the "sweet area" is generally characterized by very thick organic-rich shale, moderate thermal evolution, good preservation conditions, and shallow burial depth, which are exemplified by the shale oil and gas in the Wufeng-Longmaxi Formation, Longtan Formation, and Daanzhai Member of the Ziliujing Formation. Third, the marine, transitional, and continental shale oil and gas resources in the Sichuan Basin account for 50%, 25%, and 30% of the respective types of shale oil and gas geological resources in China, with great potential to become the cradle of the shale oil and gas industrial revolution in China. Following the "Conventional Daqing-Oil" (i.e., the Daqing oilfield in the Songliao Basin) and the "Western Daqing-Oil & Gas" (i.e., the Changqing oilfield in the Ordos Basin), the Southwest oil and gas field in the Sichuan Basin is expected to be built into a "Sichuan-Chongqing Daqing-Gas" in China. [ABSTRACT FROM AUTHOR]

Pore distribution and micro pore‐throat structure characteristics are significant for tight oil reservoir evaluation, but their relationship remains unclear. This paper selects the tight sandstone reservoir of the Chang 7 member of the Xin'anbian Block in the Ordos Basin as the research object and analyzes the pore size distribution and micro pore‐throat structure using field emission scanning electron microscopy (FE‐SEM), high‐pressure mercury injection (HPMI), high‐pressure mercury injection, and nuclear magnetic resonance (NMR) analyses. The study finds that: (1) Based on the pore size distribution, the tight sandstone reservoir is characterized by three main patterns with different peak amplitudes. The former peak corresponds to the nanopore scale, and the latter peak corresponds to the micropore scale. Then, the tight sandstone reservoir is categorized into three types: type 1 reservoir contains more nanopores with a nanopore‐to‐micropore volume ratio of 82:18; type 2 reservoir has a nanopore‐to‐micropore volume ratio of 47:53; and type 3 reservoir contains more micropores with a nanopore‐to‐micropore volume ratio of 35:65. (2) Affected by the pore size distribution, the throat radius distributions of different reservoir types are notably offset. The type 1 reservoir throat radius distribution curve is weakly unimodal, with a relatively dispersed distribution and peak ranging from 0.01 μm to 0.025 μm. The type 2 reservoir's throat radius distribution curve is single‐peaked with a wide distribution range and peak from 0.1 μm to 0.25 μm. The type 3 reservoir's throat radius distribution curve is single‐peaked with a relatively narrow distribution and peak from 0.1 μm to 0.25 μm. With increasing micropore volume, pore‐throat structure characteristics gradually improve. (3) The correlation between micropore permeability and porosity exceeds that of nanopores, indicating that the development of micropores notably influences the seepage capacity. In the type 1 reservoir, only the mean radius and effective porosity have suitable correlations with the nanopore and micropore porosities. The pore‐throat structure parameters of the type 2 and 3 reservoirs have reasonable correlations with the nanopore and micropore porosities, indicating that the development of these types of reservoirs is affected by the pore size distribution. This study is of great significance for evaluating lacustrine tight sandstone reservoirs in China. The research results can provide guidance for evaluating tight sandstone reservoirs in other regions based on pore size distribution. [ABSTRACT FROM AUTHOR]

Volume fracturing in horizontal wells represents a principal technology in the effective economic development of unconventional shale oil and gas reservoirs. However, the number of intervals that were effectively fractured by this technology only account for 20%–50% of the total designed sections. Fracture development characteristics and the factors controlling artificial fracture growth in organic-rich shale require detailed evaluation; this cannot be accomplished using microseismic monitoring technology or well-log interpretation. In this paper, formation processes of micro- and nano-scale fractures in the organic-rich shales of the Lucaogou Formation, Jimusaer Sag, Junggar Basin, northwestern China, were presented. The study focused on the application of in situ, nano-scale CT imaging technology, in combination with rock mechanics analysis. Results allowed the visualization of fracture growth in the shale reservoirs, and revealed the influence of organic matter, mineral composition, and pore structure on the formation and distribution of artificial fractures. A three-dimensional dynamic growth model of micro- and nano-scale fractures in organic-rich shale was established. Data revealed that the Lucaogou Formation shale contained dolomite and illite intragranular pores, with a low abundance of organic pores; pore size ranged between 200 nm and 2 μm. Micro- and nano-size fractures were observed. The development of artificial fractures was positively correlated with the loading stress. The initiation stress of new generated fractures was 475 mN, which could break up dolomite, albite, K-feldspar, and the original pore system as well. The original pore system was generally conducive to fracture extension and expansion. As loading stress increased from 50 mN to 515 mN, the sample extension increased from 2 μm to 14 μm, and artificial fracture width increased from 0.3 μm to 10 μm. The total porosity increased from 5.45% to 8.35%, and volume growth rate reached 53.2%. These findings provide valuable insights into the study of fracture growth in organic-rich shales, and have implications for the design of hydro-fracturing in organic-rich shales. • 3D real-time fracturing growth process with high resolution in shales is characterized. • Relationship among new fractures and pore structure & mineralogy are quantitatively evaluated, as well as fracture sizes. • Provide reference for geomechanics research and fracturing in organic-rich shales. [ABSTRACT FROM AUTHOR]

The effects of supercritical CO 2 (ScCO 2) on reservoir property changes were investigated using CO 2 –brine flow-through experiments which were set up based on the actual geological background. Inductively coupled plasma–atomic emission spectrophotometry (ICP-AES), quantitative evaluation of minerals with high-resolution scanning electron microscopy (QEMSCAN), computed tomography (CT) scanning, and physical property were adopted to develop an in situ 3D model to define porosity–mineral evolution. Variable mineral evolution, i.e., dissolution, migration, and re-precipitation of minerals and the related pore structural changes were described. All these findings have implications for the large-scale injection of CO 2 into reservoirs during enhanced oil recovery (EOR) programs and for carbon capture, utilization, and storage (CCUS) programs. • In-situ mineral and pore evolution model during CO 2 -brine-rock interaction are established. • Main dissoluted and new generated minerals are classificated and quantitatively evaluated. • Porosity changes are closely related to the total content of clay minerals. • Main minerals for carbon sequestration and storage are investigated. The effects of supercritical CO 2 (ScCO 2) on reservoir property changes of the Chang 7 Member tight sandstones of the Yanchang Formation, Ordos Basin, China, were investigated using CO 2 –brine flow-through experiments, in conjunction with detailed rock and fluid characterization (pre- and post-experiment) using X-ray diffraction mineral analysis, 3D computed tomography scanning, high-resolution scanning electron microscopy, and inductively coupled plasma–atomic emission spectrophotometry. An in situ 3D model was developed to define porosity–mineral evolution. Experiments on three contrasting samples show that minerals such as potassium (K) feldspar, albite, and calcite are variably dissolved during CO 2 –brine–mineral interactions. The dissolution, migration, and re-precipitation of clay minerals are common and are characterized by the dissolution of chlorite and the re-precipitation of kaolinite, calcium montmorillonite, and sodium montmorillonite. The original chlorite–kaolinite framework of the host rocks was destroyed. Precipitated and re-migrated clay particles (e.g., kaolinites and smectites) that were released by the dissolution accumulated in pore throats, resulting in changes to the pore system and in the physical properties of the host rocks. Physical property change pathways vary among the studied samples, with porosity being reduced by 4.5% and 12.8% or increased by 13.7% by the end of the experiments. Permeability reduction was 33.3%–81.2% and is positively correlated to host rock clay mineral content. The influence of the type and content of clay minerals on porosity requires further evaluation. The findings of the study have implications for the large-scale injection of CO 2 into reservoirs during enhanced oil recovery programs and for carbon capture, utilization, and storage programs. [ABSTRACT FROM AUTHOR]

Lacustrine tight oil resources in China are significant exploration targets, similar to the marine tight oil resources in North America, while there are clear differences in terms of the forming environment, as well as reservoir properties of these two systems. In this study, the geological characteristics of lacustrine tight rocks are discussed, including the distribution, petrology, storage space, and movable fluid saturation. The tight rocks are consisted of tight sandstone, tight carbonate rock, tight peperite, and tight sedimentary tuff, in which intergranular pores and dissolved pores with the dimensions of 30–900 nm are mainly dominated by the storage space. The oil saturation typically exceeds 50% and the oil mobility is basically controlled by pore-throats with diameter less than 1 μm. These four types of reservoirs show different potentials for tight oil, in which tight sandstone plays in the Ordos Basin and the Songliao Basin are taken as the preferred targets into account for exploration and development. Although the distribution area, physical properties, and mobility of lacustrine tight oil in China are not as good as those of tight oil in North America, the lacustrine reservoirs are often stacked in multiple layers, resulting in a great thickness, and possess relatively high oil saturation, making them producible and commercially viable. Fluid properties are critical to effectively recovery of tight oil, and more comprehensive geological evaluation on fluid mobility should be undertaken. [ABSTRACT FROM AUTHOR]

Abstract The development and evolution of porosity in organic-rich shales (ORSs) is critical to the commercial exploitation of shale oil and gas resources. In this paper, we present the results of high-temperature and high-pressure experiments on typical marine and lacustrine shales to investigate porosity changes. The samples were taken from the Proterozoic Xiamaling Formation in the North China Platform, the Permian Lucaogou Formation in the Junggar Basin, the Triassic Chang 7 member in the Ordos Basin, and the Silurian Longmaxi Formation in the Sichuan Basin, all in China. We found that the key factors influencing porosity evolution include the extent of compaction, abundance of organic matter, degree of thermal evolution, and organic matter–inorganic mineral framework. The effects of thermal evolution on the pore structure of high-mature shales are more obvious than those on low-mature shales. Although the porosity evolution is positively correlated with maturity, we found evidence for different porosity evolution in ORSs in the oil window. High-resolution scanning electron microscopy observations of experimental and actual core samples indicate that liquid hydrocarbon is adsorbed and dissolved in organic matter in the oil window, leading to swelling of the organic material. This explains why there are few organic matter pores in lacustrine shales in China. The pore structure evolution is similar for marine and lacustrine shales, suggesting that kerogen has a stronger influence on the porosity evolution of shale than does the depositional environment. The lower limit of vitrinite reflectance values (R o) at which abundant organic pores develop is 1.5%–2.5%, and the degree of pore development in ORSs is highest when R o values are 2.5%–3.0%. These results have important implications for shale oil and gas exploration. Highlights • Establish pore evolution model and investigate key factors on organic-inorganic interaction. • Describe the differences of porosity evolution between lacustrine and marine shales in China. • Provide evidence of best maturity ranges for shale oil and gas sweet-spotting. [ABSTRACT FROM AUTHOR]

Petroleum exploration targets are extending gradually from the single conventional trap reservoirs to the large-scale unconventional continuous accumulations. Oil and gas reservoirs have been divided into two types based on the trapping mechanism and distribution of oil and gas: conventional single-trap reservoirs, such as the Daqing oil field in Songliao Basin and the Kela-2 gas field in Tarim Basin; and unconventional continuous petroleum accumulation, such as Upper Paleozoic tight gas and Mesozoic tight oil in Ordos Basin, and Upper Triassic tight gas in Sichuan Basin. Two typical geologic characteristics of continuous petroleum accumulation involve: (1) coexisting source and reservoir, petroleum pervasive throughout a large area tight reservoirs, and no obvious traps or well-defined water-oil and gas contracts; (2) non-buoyancy accumulation, continuous petroleum charge, and no significant influence by buoyancy. Continuous petroleum accumulation generally have nm-scale pore throats, and the diameters range of 10-500 nm. The geometry and connectivity of these pore throats has significant impact on the migration and distribution of oil and gas in continuous petroleum accumulation. China has numerous continuous petroleum accumulation containing various petroleum deposits, and the exploration of continuous resources is very promising. Unconventional petroleum geology will become an important new subject in petroleum geology in future, and the nano-technology will function greatly on research, exploration and development of the hydrocarbon accumulation in nanopore-throats. [ABSTRACT FROM AUTHOR]

Abstract: As an important type of “conventional–unconventional orderly accumulation”, shale oil is mature oil stored in organic-rich shales with nano-scale pores. This paper analyzes and summarizes elementary petroleum geological issues concerning continental shale oil in China, including sedimentary environment, reservoir space, geochemical features and accumulation mechanism. Mainly deposited in semi-deep to deep lake environment, shale rich in organic matter usually coexists with other lithologies in laminated texture, and micron to nano-scale pores and microfractures serve as primary reservoir space. Favorable shale mainly has type I and IIA kerogens with a R o of 0.7%–2.0%, TOC more than 2.0%, and effective thickness of over 10 m. The evolution of shale pores and retained accumulation pattern of shale oil are figured out. Reservoir space, brittleness, viscosity, pressure, retained quantity are key parameters in the “core” area evaluation of shale oil. Continuously accumulated in the center of lake basins, continental shale oil resources in China are about 30×108–60×108 t by preliminary prediction. Volume fracturing in horizontal wells, reformation of natural fractures, and man-made reservoir by injecting coarse grains are some of the key technologies for shale oil production. A three step development road for shale oil is put forward, speeding up study on “shale oil prospective area”, stepping up selection of “core areas”, and expanding “test areas”. By learning from marine shale breakthroughs in North America, continental shale oil industrialization is likely to kick off in China. [Copyright &y& Elsevier]

Abstract: Considering that the air pollution risk assessment is a variable fuzzy concept with multiple indicators and classes and there is the limit for the weight value of variable fuzzy evaluation method, the variable fuzzy mathematics method and the information entropy are combined to evaluate the air pollution risk of different seasons in sixteen districts of Beijing in 2009. The multi-objective group decision-making problem under air pollution risk has been solved by variable fuzzy method and the weight problem has been modified by information entropy, which makes the evaluating results more objective. From quantitative assessment, the air pollution risk of winter season in south seven districts of Beijing was on the margin in 2009. Beijing needs to optimize energy structure by introducing and developing the use of cleaner high-quality energy to decrease air pollution risk grade on winter. [Copyright &y& Elsevier]

The characteristics of laminae are critical to lacustrine shale strata. They are the keys to the quality of source rocks and reservoirs, as well as engineering operations in shale plays. This study uses organic geochemistry, thin section identification, X-ray diffraction, field emission scanning electron microscopy, and other analytical methods, to reveal the detailed lamination texture and vertical distribution of laminae in the second Member of the Kongdian Formation in Cangdong Sag. The principal results are as follows: (1) A classification of laminae is proposed to characterize reservoir and geochemical properties. The five types of laminae are as follows: feldspar-quartz laminae (FQL), clay laminae (CLL), carbonate laminae (CAL), organic matter laminae (OML), and bioclastic laminae (BCL). There are also four significant lamina combinations (with the increasing TOC values): FQL-CLL combination, FQL-CLL-BCL combination, FQL-CLL-OML combination, and FQL-CAL-CLL-OML combination; (2) differences between laminae occur because of the variability in pore types and structures. There appears to be a greater abundance of intercrystalline pores of clay minerals in the FQL, CAL, BCL, and OML, and well-developed organic pores in the CAL and CLL, and the counterparts of intragranular pores of bioclastic material in the BCL. This detailed characterization provides the following comparative quantification of the thin section porosity of laminae in the second Member of the Kongdian Formation can be differentiated: CAL > FQL > OML > BCL > CLL; (3) differentiation between vertical distributions of laminae is carried out in a single well. The FQL and CLL are widely distributed in all the samples, while the BCL is concentrated in the upper part of the second Member of the Kongdian Formation, and CAL is concentrated in the lower part. This detailed classification method, using geochemical analysis and vertical distribution descriptions, offers a detailed understanding of lamination texture and its effects on reservoir and geochemical properties, which will provide a scientific guidance and technical support to better estimate reservoir quality and to identify new sweet spots in the second Member of the Kongdian Formation in the Cangdong Sag. [ABSTRACT FROM AUTHOR]

Abstract: The China national project of experimental advanced superconducting tokamak (EAST) has finished its construction phase and in the physical operation phase now in the Institute of Plasma Physics, the Chinese Academy of Sciences (ASIPP). The EAST is a full superconducting tokamak with a non-circle cross-section of the vacuum vessel and the active cooling plasma facing components. The project consists of a superconducting system tokamak machine, a large scale cryogenic and refrigerator system, power supply system, plasma current drive and heating system and other six subsystems. The first engineering commissioning of the EAST superconducting tokamak has been performed successfully in February 2006. The commissioning results set up the confidence to start physical operation successfully in August 2006. [Copyright &y& Elsevier]

Hydraulic fracturing has been proved to be an effective way to unlock shale gas resources. During this process, fracturing fluid comes into contact with shale reservoirs and interact with the rocks. This could cause alteration of the pore systems in shales, thereby affecting gas transport and production. To illustrate this geochemical process and identify the physical and chemical alterations of shales, fluid-shale interaction at in-situ conditions is studied for typical marine organic-rich shales from the Silurian Longmaxi Formation in the Sichuan Basin, using actual fracturing fluid and deionized water over a 5-day period. The minerals and pore structures before and after the reaction were examined by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), QEMSCAN, computed tomography (CT) scanning, nitrogen adsorption testing and organic geochemical analysis. Results showed that, the fracturing fluid and deionized water caused indiscernible changes to the organic matter, but a variety of alterations on carbonate minerals. Calcites and dolomites were markedly dissolved, but quartzs, albites and illites remained relatively unaltered. More dolomites crystals were precipitated in the deionized water-shale interaction than in the fracturing fluid-shale interaction, and some of the fractures seemed to be filled by flocculation of friction reducers or deposited mineral particles. The fracturing fluid could enlarge the pore volumes and improve pore connectivity, and the invasion depth of fracturing fluid after 120 h' was around 60 μm. The dissolved pores and loosening/shedding of particles detected by CT increased through time, and the calculated 3D pore volume increased by 67% at 24 h, 117% at 72 h, and 430% at 120 h compared to that of the initial sample. The XRD and nitrogen adsorption data indicated that new pore volumes increased with higher contents of carbonate minerals in the sample and longer treatment by fracturing fluid. The mineral and pore-scale alterations of shale reservoirs indicated that fracturing fluid-shale interaction (FFSI) enlarged the reservoir reconstruction volume, increased well performance during shut-in period and should be considered as part of the well treatment optimization process. • The evolutionary pattern of mineral-pore is identified under in situ geological conditions. • Carbonate minerals dissolved significantly, while other components remained unaltered. • The porosity increased after the interaction between shales and fracturing fluid. [ABSTRACT FROM AUTHOR]

Large accumulations of oil and gas have been found in fan delta conglomerate reservoirs in the upper Triassic Baikouquan Formation in the Mahu Sag at the northwestern margin of the Junggar Basin. To effectively explore strongly heterogeneous, high-quality, conglomerate reservoirs, their deposition, diagenesis, and genetic mechanisms must first be thoroughly studied. Analyses of cores, thin sections, fluid inclusions, oxygen isotopes, logging, physical properties data, X-ray diffraction, scanning electron microscopy, and cathodoluminescence confirm that the conglomerates have high feldspar contents as well as volcanic fragments that comprise a variety of micro-lithofacies. The heterogenous reservoir properties include permeability values of less than 1 mD, 1–10 mD, and higher than 10 mD, which correspond to 44.19%, 37.06%, and 18.75% of the reservoir, respectively. The tight reservoirs, mostly developed in the fan delta plain, have experienced extensive compaction and/or calcite cementation and consist of only a few secondary pores. Reservoirs with high porosity and permeability developed in subaqueous channels and experienced relatively weak compaction. These reservoirs contain large numbers of secondary pores that were mainly formed by the dissolution of K-feldspars and volcanic rock fragments. Comprehensive studies of sedimentation and diagenesis in the Baikouquan Formation indicate that these high porosities originated from the chronological coupling of the following three important geological processes: (1) Conglomerate reservoirs with better sorting and roundness and lower mud content are mainly developed in subaqueous distributary channels and have higher porosity and permeability than reservoirs with poorer sorting and roundness. (2) Strong dissolution of K-feldspar and volcanic debris occurred in reservoirs with good original physical properties, forming large numbers of secondary pores. Acidic fluids from source rocks in the Fengcheng Formation led to dissolution. (3) The byproducts of dissolution, which consist mostly of mixed-layer illite/smectite and illite, reduced porosity and permeability. In reservoirs with good original physical properties and fault development, dissolution plays an obvious role in improving physical properties in such relatively open diagenetic systems. • Conglomerate reservoir heterogeneity is very strong. • The dissolution in Lithofacies 3 can promote the porosity. • Compaction, calcite and clay mineral are the primary factors to destroy the porosity. [ABSTRACT FROM AUTHOR]

The characteristics of fracture propagation in heterogeneous tight sandstones are critical to volumetric fracturing, which is the key to unlocking unconventional resources in tight sandstones. Quantification of the influence of pre-existing pore systems and particle arrangements on the propagation of fractures is challenging due to inadequate imaging of the internal void systems in tight sandstones from three-dimensional (3D) aspect. In this study, the 3D geometry of tight sandstones from the Chang 7 member in the Ordos Basin is continuously imaged under different loading stresses, and the voxel resolution of the X-ray computed tomography is 2.5 μm. The data set captured in this process shows the changes in the samples at the microstructural level as they approach fracturing. The data are stored as a time series of 3D images. The results demonstrate that: (i) fractures propagate progressively and gradually link with pre-existing pores, resulting in macroscopic fractures with a maximum width of 250 μm, while newly generated fractures could break up particles and may not follow the line of pre-existing fractures; and (ii) three stages were identified in the failure process of tight sandstones, with new fractures running at an angle of about 30° to the general direction of the stress of compression. The total volumes of both the sample and pore-fractures, and the damage index, which were extracted from the 3D images, all increased when approaching fracturing. The final volume of pore-fracture systems could be 11 times that of the initial pore volume. All of these observations provide valuable insights and design guidelines for hydraulic fracturing in unconventional tight sandstones, and a quantified model of the dynamics and the morphology of fracture propagation with increasing stress approaching failure, which may shed light on dynamic critical transitions in the Earth's crust. • An in situ three-dimensional fracture propagation model during loading stress is established. • Three stages are distinguished in the failure process of tight sandstones. • Fractures propagate progressively and gradually link with pre-existing pores. [ABSTRACT FROM AUTHOR]

The Permian formation in the Junggar Basin contains the oldest continental shale in China and has abundant petroleum resources. The lithofacies and lithology of the shale strata in the Lucaogou Formation, which are characterized by two sets of coexisting combinations of tight oil and shale oil in the Jimsar Sag, eastern Junggar Basin, are studied via experiments to explore their petrophysics, geochemistry, reservoir pores, and oil-bearing properties. The results show that (1) the Lucaogou Formation in the Jimsar Sag consists of shallow-deep lacustrine sediments and can be divided into six stratigraphic units vertically; 2) fine-grained sediments in the sag composed of shale, dolomite, and siltstone can be specifically divided into carbonate mudstone (CM), siliceous mudstone (SM), carbonate rock (CC), carbonate sandstone (CS), and siliceous sandstone (SS); (3) CM and SM are good source rocks for shale oil, and P 2 l 2 and P 2 l 5 are the "sweet sections" for shale oil; CC, CS, and SS are reservoirs of tight oil, and P 2 l 1 and P 2 l 4 are the "sweet sections" for tight oil. Finally, definitions are discussed and proposed for tight oil and shale oil. • The stratigraphic units, Lithofacies and lithology of ancient continental Permian Lucaogou Fm. are divided and compared. • There are two sets of coexisted combination of tight oil and shale oil in Permian Lucaogou Fm., and the "sweet sections" are selected. [ABSTRACT FROM AUTHOR]

Tight oil and shale oil are the important unconventional resources in shale systems, in which the tight oil is the most realistic and profitable resources. Due to special geological environments, lacustrine tight oil is different from marine tight oil in North America. Sweet-spotting is critical to develop these abundant resources, in which three aspects including geology, engineering and economy have been taken into consideration. In this paper, we proposed the definition of sweet spot zone and sweet spot interval in shale system, and discuss the geological significance & related technologies. Tight oil and shale oil should be assessed as a whole system during the future geological evaluation and technology development. The productivity of tight oil and shale oil will be increased by 30–50 million tons, making the economic development of oil in continental shale systems in China. • The world-level lacustrine tight oil accumulations in China. • Geological aspects of tight oil in shale systems. • Critical evaluation and development technologies for sweet spotting. Crude oil in unconventional shale systems, present as tight oil and shale oil, accumulates inside an oil kitchen in formations with coexistent sources and reservoirs. Organic matter present in oil shale is not yet mature and requires heating to convert it into crude oil. Oil exploration in shale systems involves the exploration of shale oil retained in source rocks and tight oil rich zones located near source rocks. Tight oil is a type of realistic unconventional oil resources in China. The marked increase in potential shale oil reserves, and exploration of these reserves, will result in a shale oil revolution similar to that experienced for shale gas. Based on a systematic comparison of geologic features of shale systems in the US and China, the geologic significance of the sweet spots in shale systems is proposed. This zone contains an abundance of unconventional oil in shale systems that can be explored and developed under current economic and technical conditions. The sweet spot zone refers to the zone in the tight oil rich zone which has industrial value within the scope of matured high-quality source rocks on the plane. The sweet spot interval refers to the high-productivity interval of tight oil which has industrial value through artificial stimulation. The main aim of oil exploration in shale formations is to identify the sweet spots. The distribution of the economic sweet spots in shale systems is evaluated by overlapping the geologic, engineering and economic sweet spots. Resource assessment techniques, the identification of logging data properties, high-resolution 3D seismic surveys, horizontal well production from well pads, and artificial reservoir development of sweet spots in oil-bearing shale formations can assist efficient development of oil. Globally, shale formations contain a significant volume of oil reserves. Currently, stimulated reservoir volume (SRV) techniques in horizontal wells in marine shale gas formations in the United States have average peak-productivity cycles of 10–15 years. To achieve commecial oil production in lacustrine shale systems in China, it is important to utilize large formation thicknesses and the high abundance of organic matter. In addition, the development of practical and economic techniques will result in an increase of productivity of tight oil and shale oil by 30–50 million tons, as well as the economic development of oil in lacustrine shale systems in China. [ABSTRACT FROM AUTHOR]

• Multipel controlling factors of organic matter accumulation are summrarized. • Characteristics of tight reservoir are discribled in by multiple-scale approaches. • Based on the case study on Junngar basin, the tight oil "sweet pot" is evaluated. Tight oil in China is mainly distributed in Mesozoic-Cenozoic continental petroliferous basins, either generally occurs in tight sandstone or tight carbonate reservoirs which are paragenetic to or in contact with lacustrine petroleum source rocks. By the end of 2016, the continental tight oil in China has established an annual production capacity of 1.55 million tons, and a cumulative oil production of 2.52 million tons. In 2016, the continental tight oil production in China was about 800,000 tons. By analyzing the characterization of the tight oil in Ordos Basin, Songliao Basin, Jungar Basin, the organic-rich shale in China were formed in multiple geological periods including the Permian, Triassic, Jurassic, Cretaceous, Neogene, and Paleogene, in freshwater, semi-saline to hyper-saline lacustrine depositional setting. They are generally tens of meters to several hundreds of meters thick, have total organic carbon (TOC) contents of 0.4–16%, and thermal maturity of 0.4–1.4%. Algal bloom as results of volcanism, low sedimentation rate, transgression, and stratification of water body are prominent factors controlling the formation of organic-rich shales. Tight oil reservoirs in China mainly include tight sandstone, tight carbonate rock, tight sedimentary tuff, etc., all of which are characterized by strong heterogeneity and poor petrophysical properties, with in situ porosity and permeability generally no more 12% and 1 × 10−3 μm2 respectively. They are also characterized by tight pore-throat systems of nano- to micro-scales, with pore throat diameters in the range of 80–1800 nm, and complex pore structures. The producing reservoirs have pressure coefficients between 0.7 and 1.8, covering under-pressure to over-pressure. Crude oil properties vary greatly with densities ranging from 0.75 to 0.92 g/cm3. It is believed that the abundance and effectiveness of hydrocarbon supply controls the formation of oil saturation, and tight oil "sweet spots" are generally in or near the areas with high hydrocarbon expulsion intensities. In addition, the quality of the source rock and the type of source reservoir control the distribution of the "sweet spots", and storage space and movable fluid guarantee the formation of the "sweet spot" area of high oil saturation. "Sweet spots" are often developed in local mini-structural highs under a broad and gentle-sloped background. Continental tight oil in China has estimated geological resource of 14.66 × 109 tons with a technically recoverable resource of 1.45 × 109 tons. Tight oil is mainly distributed in Ordos Basin, Songliao Basin, Bohai Bay Basin, Junggar Basin, and Qaidam Basin, within the Mesozoic and Cenozoic formations. Overall China has a relatively large tight oil reserve and good exploration prospect. [ABSTRACT FROM AUTHOR]

Abstract Organic-matter-rich shales are the main target rocks for unconventional oil and gas exploration and development across the world. In China, shale-gas geological resources are estimated as approximately 110 × 1012 m3, with recoverable gas reserves of ca. 20 × 1012 m3. Recoverable shale-oil reserves are estimated as ca. 5 × 109 t. A total 35 important organic-matter-rich shale units have been recognized from Mesoproterozoic to Cenozoic strata across the entire China. These shales are categorized according to their origin under marine, marine–nonmarine transitional and lacustrine conditions. Shales of marine origin, with ca. 9 × 1012 m3 recoverable resources, dominate China's potential in terms of total volume of organic-carbon. Currently, the most favorable marine shales for oil and gas exploration are found in the Sichuan Basin within the lower Cambrian Qiongzhusi Formation and in the Wufeng-Longmaxi formations of uppermost Ordovician through lower Silurian. A fortuitous combination of of sea-level variations, of paleo-productivity, of tectonic activity causing development and migration of partially closed deep basin depocenters, and of sediment accumulation rates controlled the extensive deposition and distribution of organic-matter-rich shales in these Wufeng and Longmaxi formations. Organic-matter-rich shales in marine-nonmarine transitional facies associated with coal measures occur in North China within the Carboniferous and Permian, and in South China within the Permian. These Carboniferous-Permian organic-matter-rich shales are important source rocks for the gas fields in the Ordos and Sichuan Basins. Abundant organic-rich shales are also widely distributed within coal-bearing clastics and coal-measure shales of fluvial, lacustrine, and swamp facies in Upper Triassic to Middle Jurassic successions of many basins. Lacustrine organic-rich shales were deposited during the Permian through Neogene in various freshwater to saline lake settings. Lacustrine organic-matter-rich shales are the main oil source rocks in the Songliao, Bohai Bay, Ordos and Junggar basins. Lacustrine algae contributed to the rain of organic matter; and the preservation of organic matter and distribution of organic-rich shale was controlled by lake currents, water depth and oxygen-poor conditions, with enhanced preservation when buried by turbidity currents. Algal blooms were partly induced by trace nutrients from volcanic ash falls in all of these lacustrine basins. Seawater intrusion into the freshwater lake of the Songliao Basin promoted some episodes of black shales. Saline lacustrine basins, such as middle Permian Junggar Basin, contain organic-rich dolomite mudstone that mainly formed during hot climate conditions when the lakes had high salinity and stratified water columns that deprived the bottom waters of oxygen, thereby preserving massive amounts of organic matter. Laminated calcite-rich mudstone in the saline lacustrine settings formed in more brackish waters under stable warm conditions and weak biological activity. The modeling of the factors controlling the distribution of organic-matter-rich shales within China's basins is important for the exploration and development of unconventional oil and gas resources. [ABSTRACT FROM AUTHOR]

• Stromatolite, thrombolite and granular microbialite were TOP three microbial dolostones in Mesoproterozoic system. • The agitated depositional environment is favourable for porosity evolution. • The effective reservoir interval is normally located in the lower part of a peritidal microbial facies succession. There are three main types of microbial dolostones in Mesoproterozoic Wumishan Formation in Jixian, North China. They are stromatolite, thrombolite and granular microbialite. The microbialite lithofacies are intensely environmentally associated. Several kinds of stromatolite can be found in the peritidal environments. Mostly planar or wavy stromatolites show in intertidal and supratidal zones while domy and conic stromatolites occur in subtidal or lower intertidal zones. In more agitated subtidal zone or tidal channels, microbial grains deposited, such as thrombolite, oncolite, and sand- gravel sized microbial-coated grains. The intraclasts related laminite facies mostly deposited in shallow subtidal zone. Representative four outcrop sections of Wumishan Formation in Jixian are measured and documented. The petrophysical and petrological study from the outcrop and well core samples reveals that the reservoir rocks are closely related to lithofacies and their depositional environments. The more agitated the depositional environment is, the better the reservoir quality, even so that after the diagenesis (surface and burial). The dolostone porosity of planar stromatolite in supratidal and intertidal are much worse than the subtidal high-agitated microbialite rocks, whether samples from the outcrops or drilling cores. The effective reservoir interval is normally located in the lower part of a peritidal microbial facies succession, mainly consists of subtidal microbialite, such as thrombolite, thrombo-stromatolite, oncolite, columnar stromatolite and coated intraclastic grainstone and rudstone, commonly deposited in agitated environment. The thickness of reservoir rocks in microbialite para-sequences ranges commonly from 4 to 14 m, deeply related to depositional cycles or sequence stratigraphy in vertical lithofacies texture and their areal extent to the paleogeography. [ABSTRACT FROM AUTHOR]

• Description of the configuration of the CFETR machine. • Description of design status of CFETR key components, including magnet system, blanket system, divertor system, remote handling system, vacuum vessel, thermal shield and cryostat. • Description of the engineering design of CFETR machine. The China Fusion Engineering Test Reactor (CFETR) is the next step in China's roadmap for magnetic confinement fusion development. It aims to bridge the gap between the ITER fusion experimental reactor and the demonstration fusion power reactor (DEMO). The CFETR will be operated in two phases. Phase I aims to achieve fusion power of 50–200 MW, Q plasma = 1–5, TBR > 1.0 and neutron irradiation effects ∼ 10 dpa. Phase II aims to perform tokamak DEMO validation under fusion power > 1 GW, neutron irradiation effects ∼ 50 dpa and figQ plasma > 10. To ensure that the CFETR machine can achieve these goals, the major/minor radii of plasma have been altered from R = 5.7 m/a = 1.6 m to R = 7.2 m/a = 2.2 m. The new machine can meet the targets of both Phase I and Phase II and achieve smooth transfer between them. The configuration of the CFETR machine is presented in this paper. Then, the design progress and status of some key components are described, including the magnet system, blanket system, diverter system, remote handling system, vacuum vessel, thermal shield and cryostat. The research and development of most components are underway and will be demonstrated in the near future. [ABSTRACT FROM AUTHOR]

Unconventional shale/tight oil resources in fine-grained sedimentary rocks play essential roles in global energy structure. Fine-grained sedimentary rocks are characterized by complex pore assemblage and connectivity. Insights into the links between pore structure and movable oil are important for exploration and production of tight/shale oil or gas in fine-grained sedimentary rocks. A series of analyses including thin sections, mercury injection capillary pressure (MICP), and nuclear magnetic resonance (NMR) were carried out to unravel the linkage between pore structure and oil movability. Various centrifugation speeds were used in the NMR tests to remove the movable oil to obtain the movable oil saturation corresponding to various centrifugation speed. Fractal dimension is calculated from NMR T 2 spectrum. Then four types of pore structures were divided according to the parameters derived from the MICP and NMR results, and the characteristics of various pore structure are summarized. From type Ⅰ to type Ⅳ, the threshold pressure, irreducible water saturation (S wi), and the fractal dimension increased while the S Hgmax , r apex , T 2gm , porosity, permeability, and movable oil saturation decreased. Then the key factors controlling the movable oil saturation were investigated, including permeability, porosity, T 2gm , r apex , and mineral composition of the rocks. The movable oil saturation is dominated by porosity, T 2gm , fractal dimension, and r apex. Then a quantitative evaluation model of the movable oil saturation was established. In addition, the NMR logs and the derived parameters were utilized to evaluate the reservoir quality and pore structures in a single well. At last the T 2 value of 25 ms (the ratio of the T 2 components >25 ms to the total T 2 components) was used to calculate the movable oil saturation in the upper member of the Lucaogou Formation, and the T 2 value of 28 ms was used for the lower member of the Lucaogou Formation in the Jimusar Sag. The results are testified by the high-speed (10000 r /min) centrifugation NMR measurements. The results above help improve understanding of tight/shale oil enrichment and provide a new model for calculating the movable oil saturation in fine-grained sedimentary rocks. • The reservoir quality decreases from type Ⅰ to type Ⅳ pore structure. • The main controlling factors of movable oil saturation are porosity, fractal dimension, r apex and T 2gm. • The NMR logs can be used to calculate the movable oil saturation. • The T 2 value calculating the movable oil saturation is different in the upper and lower sweet spot. [ABSTRACT FROM AUTHOR]

Authigenic chlorite plays an important controlling role in reservoir quality, and is widely distributed in the tight sandstone reservoirs of the Triassic Yanchang Formation in the Southwestern Ordos Basin, China. The occurrence and origins of authigenic chlorite were investigated using an integrated approach of optical microscopy, scanning electron microscopy, X-ray diffraction, electron probe microanalysis, and fluid inclusion analysis. The sandstones are fine-grained lithic arkoses and feldspathic litharenite with 11.5% volcanic rock fragments. Authigenic chlorite occurs in two morphotypes, including pore-lining and pore-filling chlorite. Pore-lining chlorite occurs as coatings on the framework grains and covers the entire fining-upward sandstones. Pore-filling chlorite is restricted to the middle to upper part of the fining-upward sandstones and appears as discrete flaky plates or rosettes in the pores or attaches to the surfaces of pore-lining chlorite. Pore-lining chlorite originated from smectite precursors that were derived from volcanic material alteration in the early stage of diagenesis, with temperatures primarily about 90 °C. In contrast, pore-filling chlorite was precipitated in pore spaces with higher concentrations of Mg2+ and Fe2+ released from volcanic rock fragments and mica debris dissolution. Moreover, the chemical composition of pore-filling chlorite was affected by early calcite cementation which consumed some ions at temperatures lower than about 110 °C. The thin and continuous pore-lining chlorite is the only chlorite type with a positive effect on reservoir quality, whereas the very thick pore-lining chlorite (>6.7 μm) or pore-filling chlorite significantly reduce the porosity and permeability. Systematic studies of authigenic chlorite can provide important insights into the reservoir heterogeneity and are applicable to the exploration and development of tight oil. • Performed a detailed investigation on types and distribution of authigenic chlorite. • Clarified the origin of two generations of authigenic chlorite. • Determined the impact of authigenic chlorite on reservoir heterogeneity. [ABSTRACT FROM AUTHOR]

Understanding reservoir heterogeneity and associated diagenesis, have a paramount importance for efficient petroleum exploration and development strategies. Diagenetic variations and factors that control these processes have, therefore, been investigated in this study using petrographic and geochemical methods, including cathodoluminescence, scanning electron microscopy, x-ray fluorescence, electron probe microanalyses and stable isotope analysis. Mechanical compaction and chemical diagenesis trends have obviously varied as a function of rock types and geological locations. The conglomerate reservoirs with high content of tuffaceous matrix and characterized by poor sorting showed stronger compaction. The tuffaceous matrix displays a large degree of dissolution during the progressive burial diagenesis due to its thermodynamic instability. The tuffaceous matrix in Na-rich conglomerate reservoir rocks mainly transformed into analcite, while it transformed into illite in K-rich conglomerate reservoir rocks. In most conglomerate reservoirs far away from deep-rooted faults, calcite cements are indicated to have been sourced from the decarboxylation of organic matter in the interbedded mudstones. Carbonate cements in conglomerate reservoirs near the deep-rooted faults possibly formed from hydrothermal fluids or thermochemical oxidation of pre-existing methane accumulations. This study can serve us an excellent example for the control of sediment composition and paleo-fluid evolution on diagenetic variations in fan-delta conglomerate reservoirs. • Compaction and dissolution in conglomerate reservoirs were controlled by sediment composition and texture. • Authigenic silicoaluminate minerals formation in conglomerate reservoirs were controlled by sediment composition. • Carbonate cements formation in conglomerate reservoirs were controlled by paleo-fluids evolution. [ABSTRACT FROM AUTHOR]

• Three lamination types are distinguished in the Upper Ediacaran botryoidal dolostones in Western Yangtze Platform. • EPS and filaments are documented in botryoidal laminae which were previously believed to be abiogenic origin. • Different microbial mineralization types are recognized in different botryoidal laminae. Botryoidal dolostones are abundant in the Second Member of the Upper Ediacaran Dengying Formation in the Western Yangtze Platform. Although they have been extensively discussed as important host rocks for giant gas reservoirs, there is no consensus on the microbial impact on mineralization processes in the botryoidal laminations. Typical botryoidal laminations were studied under optical microscopes and scanning electron microscopes (SEMs) to investigate their origin. There are three macroscopic morphological types of botryoidal lamination: stromatoid lamination, cavity-lining lamination, and spherical-encrusting lamination. These three types of lamination are composed of fibrous and bladed crystals growing perpendicular to the botryoidal laminae, which have hitherto been implicitly considered to be from abiogenic chemical precipitation. There are many lines of new evidence that demonstrate microbial activities in the interbedded dark and bright laminae constituting the laminations. In the dark laminae, euhedral dolomite rhombs are observed sticking to linear and tubular filaments, or wrapped in sheets of extracellular polymeric substances (EPS) with dolomite crystal sizes of generally <5 μm. The bright laminae are dominated by coarser dolomites and connected by radial sheaths and trichomes with dolomite crystal sizes of primarily around 10 μm. Different species of bacteria, which are closely related to the macroscopic morphology of the laminations, are present in both the bright and dark laminae. The results are useful in understanding the origin and formation mechanisms of the Neoproterozoic botryoidal dolostones. The new findings may also shed new light on the occurrence and evolution of early life on Earth in the Precambrian Era. [ABSTRACT FROM AUTHOR]

Unlabelled: Our research aimed to look into the clinical traits and genetic mutations in sporadic non-syndromic anodontia and to gain insight into the role of mutations of PAX9, MSX1, AXIN2 and EDA in anodontia phenotypes, especially for the PAX9., Material and Methods: The female proband and her family members from the ethnic Han families underwent complete oral examinations and received a retrospective review. Venous blood samples were obtained to screen variants in the PAX9, MSX1, AXIN2, and EDA genes. A case-control study was performed on 50 subjects with sporadic tooth agenesis (cases) and 100 healthy controls, which genotyped a PAX9 gene polymorphism (rs4904210)., Results: Intra-oral and panoramic radiographs revealed that the female proband had anodontia denoted by the complete absence of teeth in both the primary and secondary dentitions, while all her family members maintained normal dentitions. Detected in the female proband were variants of the PAX9 and AXIN2 including A240P (rs4904210) of the PAX9, c.148C>T (rs2240308), c.1365A>G (rs9915936) and c.1386C>T (rs1133683) of the AXIN2. The same variants were present in her unaffected younger brother. The PAX9 variations were in a different state in her parents. Mutations in the MSX1 and EDA genes were not identified. No significant differences were found in the allele and genotype frequencies of the PAX9 polymorphism between the controls and the subjects with sporadic tooth agenesis., Conclusions: These results suggest that the association of A240P with sporadic tooth agenesis still remains obscure, especially for different populations. The genotype/phenotype correlation in congenital anodontia should be verified.