The Middle Triassic Ordos Basin witnessed the earliest rehabilitation of complex lacustrine ecosystems after the end-Permian mass extinction (EPME). The specific challenges faced by freshwater ecosystems during this interval remain unclear, however, owing to the limited spatiotemporal coverage of integrated biogeochemical studies. Here, we combine high-resolution geochronology, mineralogical and multi-proxy geochemical data from the mid-Triassic Ordos Basin with temporal and spatial biogeochemical modelling to reconstruct lake redox structure and nutrient dynamics. Our results indicate that a transient increase in external sulfate input strengthened endogenous phosphorus recycling and eutrophication, promoting shoaling and intensification of a metastable sulfidic zone at mid-depths. This shoaling would have led to poisoning of benthic habitats, causing a collapse of the oldest known Mesozoic lacustrine ecosystem. We propose that sulfate loading prolonged anoxia and ecological stress by extending the residence time of phosphorus, a mechanism that may be relevant to deoxygenation events and resulting biocrises in both ancient and modern lacustrine ecosystems.

Formation fluid significantly influences the thermal conductivity distribution of rocks under in-situ conversion conditions. Current thermal conductivity measurements are primarily conducted on rocks, or are limited to a single component of crude oil or purified water. In this study, we selected oil and formation water samples of the Yanchang Formation, Ordos Basin to investigate dynamic evolution of thermal conductivity under varying temperature and pressure conditions. An innovative hot-wire method was employed, based on fundamental analysis of fluid physical properties and composition. The results reveal distinct differences in the thermal conductivity between crude oil and formation water. Specifically, the thermal conductivity of crude oil decreases with increasing temperature, whereas that of the formation water first increases and then decreases. This behavior is governed by the density and acoustic velocity of the fluids. Pressure also exerts a significant effect on the thermal conductivity of both the crude oil and formation water, primarily by inducing phase transition and impairing heat transfer. Empirical equation describing the evolution of thermal conductivity under varying temperature and pressure conditions was established, and a corresponding evolution mechanism is proposed. These findings provide valuable references for optimizing temperature and pressure conditions, as well as for the design of mining technologies in in-situ shale conversation systems.

Shale reservoirs offer significant potential for CO2 geological sequestration due to their extensive nanopore networks and heterogeneous pore systems. This study comparatively assessed the CO2 storage potential of the Lower Silurian Longmaxi and Lower Cambrian Qiongzhusi shales through an integrated approach involving organic geochemical analysis, mineralogical characterization through X-ray diffraction (XRD), mercury intrusion capillary pressure (MICP), low-pressure nitrogen and carbon dioxide physisorption, field-emission scanning electron microscopy (FE-SEM), stochastic 3D microstructure reconstruction, multifractal analysis, and three-dimensional succolarity computation. The results demonstrate that mineral assemblages and diagenetic history govern pore preservation: Longmaxi shales, with moderate maturity and shallower burial, retain abundant organic-hosted mesopores, whereas overmature and deeply buried Qiongzhusi shales are strongly compacted and mineralized, reducing pore availability. Multifractal spectra and 3D reconstructions reveal that Longmaxi develops broader singularity spectra and higher succolarity values, reflecting more isotropic meso-/macropore connectivity at the SEM scale, while Qiongzhusi exhibits narrower spectra and lower succolarity, indicating micropore-dominated and anisotropic networks. Longmaxi has nanometer-scale throats (D50 ≈ 10–25 nm) with high CO2 breakthrough pressures (P10 ≈ 0.57 MPa) and ultra-low RGPZ permeability (mean ≈ 1.5 × 10−2 nD); Qiongzhusi has micrometer-scale throats (D50 ≈ 1–3 μm), very low breakthrough pressures (P10 ≈ 0.018 MPa), and much higher permeability (mean ≈ 4.63 × 103 nD). Storage partitioning further differs: Longmaxi’s median total capacity is ≈15.6 kg m−3 with adsorption ≈ 93%, whereas Qiongzhusi’s median is ≈12.8 kg m−3 with adsorption ≈ 70%. We infer Longmaxi favors secure adsorption-dominated retention but suffers from injectivity limits; Qiongzhusi favors injectivity but requires reliable seals.

The evolution of the Triassic megamonsoon was closely linked to Earth's orbital variations. Despite recognizing secular orbital cycles as a fundamental pacemaker of the megamonsoon, the driving mechanisms remain unclear. Here, we use data-model synthesis to study orbital-scale megamonsoon variability during the Middle Triassic (~ 246-239 Ma). By integrating high-resolution reconstructions of hydrologic fluctuations, obtained from lithological and magnetic susceptibility data series in the lacustrine sediments of the Ordos Basin (Northeast Tethys), with the climate simulations, we identify monsoon cycles in the ~ 20, 100, and 405 kyr Milankovitch bands. Comparisons with other records further reveal an additional eccentricity-related ~ 3.3 Myr orbital cycle in monsoon variabilities, temperature oscillations, carbon cycles, and sea-level changes. Earth system models show the effects of orbital configurations and atmospheric CO₂ concentrations on megamonsoon dynamics, implying threshold responses to solar radiation and the impacts of temperature and sea-level fluctuations on long-term megamonsoon variability. These findings improve our understanding of the interplay between astronomical forcing and feedbacks in shaping orbital-scale monsoon dynamics.

The high-quality laminated source rock organic matter (OM) originated from planktonic algae, and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Qaidam Basin. However, coupling research on the paleoenvironment change and OM enrichment during the sedimentation period of the source rock is still lacking. This study from the aspects of sedimentary petrology, geochemistry and paleontology palynology, the paleoenvironment of source rock is restored and the OM enrichment model is established in the study area. Firstly, kerogen maceral identification indicates that the kerogen maceral is mainly composed of Botryococcus, accompanied with amorphous organic matter and plant debris. Secondly, arid climate and relatively active tectonic were observed during the deposition of the source rock. The water column was received felsic source from the continental island arc tectonic background, and has the environmental characteristics of relatively saline, shallow depth, medium low productivity, fast sedimentation rate and anoxic reduction and so on. Lastly, the first-order controlling factors for the OM enrichment are anoxic water conditions and suitable sedimentation rate, and the secondary controlling factor is paleoproductivity. Through the coupling study of paleoclimate, paleoenvironment and OM enrichment, the paleoclimate high frequency alternating evolution was the root cause of sedimentary environment change and OM enrichment of the laminated shale in the Upper Xiaganchaigou Formation. The study on the OM enrichment mechanism of algae in Qaidam provides a good model for understanding the coupling relationship between the algae bloom in the saline lake basins and the environments, and provides important theoretical basis for predicting shale oil “sweet spot” and production well sites arrangement for the continental saline lacustrine basins.

In this study, an innovative breakthrough pressure detection system for shale oil is introduced. Experiments were conducted on source rocks from three main rock types in the upper member of the Lower Ganchaigou Formation in the Western Qaidam depression, in Qinghai, China. The results show that the differences between the breakthrough pressures of laminated calcareous mudstone (LCM), siltstone (SS), and massive mixed mudstone (MMM) in the formation are of several orders of magnitude. In particular, the shale oil breakthrough pressure of laminated calcareous mudstone is more than five times greater in the vertical bedding direction than in the horizontal bedding direction. As black medium shale oil turns into yellow light shale oil, the breakthrough pressures in the same lithology and direction are reduced by two-thirds. In laminated mudstone the horizontal breakthrough pressure is lower than the vertical, while in massive mixed mudstone the vertical breakthrough pressure is lower. A composite migration model for shale oil in hybrid strata-horizontal migration along bedding and vertical migration through micro-fractures-is proposed. The results are of great significance for understanding the accumulation of shale oil and for identifying exploration targets.

Through investigating the Triassic Yanchang Formation in the Ordos Basin, black carbon has been found for the first time in the seventh member of the Middle Triassic Yanchang Formation (Chang 7 Member). This study suggests that the oxygen content in the East Tethys during the Middle Triassic was beyond 15% and that plants had recovered from the Late Permian mass extinction. The results show that the distribution of black carbon in the Chang 7 Member is heterogeneous in the basin. In the southeastern part, the black carbon content is the highest (possibly higher than 6%) in shale, with the proportion in total organic carbon content (TOC) up to 20%, which is lower than 10% in the northwestern and northeastern parts. The traditional practice needs to be re-evaluated when using TOC as a critical index in source rock evaluation and shale oil and gas sweet spot screening. Shale with high TOC may not necessarily be effective source rocks and or attractive targets for unconventional oil and gas exploitation, whereas those with low TOC could potentially be effective or high-quality source rocks. The TOC in shale can be divided into mass fractions of black carbon (wb), active carbon (wa), residual carbon (wr), and carbon from mature shale oil (wo). TOC-wb is recommended for evaluation of source rock, wa for screening the in-situ recovery area of low to medium maturity shale oil, and wo for appraisal of the favorable exploration area of medium to high mature shale oil. These results allow for the quantitative evaluation of organic matter composition of shale, hydrocarbon generation potential, maturation stage, and generation, expulsion and retention of shale oil, and also guide the reconstruction of climate in the source rock development period and the shale oil and gas sweet spot screening.

Using high-precision zircon U-Pb ID-TIMS geochronology, tuffs from the Chang 9 shale and the Chang 7 shale were dated. The tuff in the Chang 9 shale is 241.47 ± 0.17 Ma, which falls between the top tuff age of 241.06 ± 0.12 Ma and the bottom tuff age of 241.558 ± 0.093 Ma in the Chang 7 shale. These reveal that the Chang 9 and Chang 7 shales are contemporaneous, belonging to the Ladinian stage of the Middle Triassic. This insight expands the region of the main source rock of Chang 7 to the northeast and will inform the search for the deep Chang 9 shale petroleum system, increasing the scope for exploring the Chang 7 shale system in northern Shaanxi. The research results clarify the relationship between the two sets of shale in the Yanchang Formation and redefine the distribution range of the Chang 7 shale in the Ordos Basin. At the same time, it shows that there is a cross-layer problem in the stratigraphic division of the Yanchang Formation in different regions, the high-precision U-Pb dating technology providing a reference for the fine stratigraphic correlation of other continental basins in the world.

Through core observation, thin section identification, and logging and testing data analysis, the types and characteristics of event deposits in the ninth member of Yanchang Formation of Triassic (Chang 9 Member) in southwestern Ordos Basin, China, are examined. There are 4 types and 9 subtypes of event deposits, i.e. earthquake, gravity flow, volcanic and anoxic deposits, in the Chang 9 Member in the study area. Based on the analysis of the characteristics and distribution of such events deposits, it is proposed that the event deposits are generally symbiotic or associated, with intrinsic genetic relations and distribution laws. Five kinds of sedimentary microfacies with relatively developed event deposits are identified, and the genetic model of event deposits is discussed. Seismites are mainly developed in the lake transgression stage when the basin expands episodically, and commonly affected by liquefaction flow, gravity action and brittle shear deformation. Gravity flow, mainly distributed in the high water level period, sandwiched in the fine-grained sediments of prodelta or semi-deep lake, or creates banded or lobate slump turbidite fan. It is relatively developed above the seismites strata. The volcanic event deposits are only seen in the lower part of the Chang 9 Member, showing abrupt contact at the top and bottom, which reflects the volcanic activity at the same time. Anoxic deposits are mostly formed in the late stage of lake transgression to the highstand stage. Very thick organic-rich shales are developed in the highstand stage of Chang 9 Member, and the event deposits in the depositional period of these shales are conducive to potential reservoirs.

鄂尔多斯盆地三叠系延长组石油年产量超3500×104t,然而该主力产层现行的"标志层约束、油层组等厚劈分"划分方案,在油气勘探开发实践中受到挑战.作者利用不同沉积体系长7油层组内凝灰岩定年数据和盆地庆城北地区新采集的高品质三维地震数据体,开展同位素年代学研究和钻井资料约束下的高精度地震地层解释.锆石定年结果表明盆地东南部长7油层组属于中三叠世,锆石ID-TIMS定年可实现不同沉积体系高精度地层对比.同时,在庆城北三维工区延长组长2油层组底至长73油层组顶解释识别出11个前积地质体,刻画出长7油层组中6个前积体进积演化规律.针对延长组陆相地层等时划分难点,提出建立不同物源体系长7油层组高精度地层定年"锚点",利用提频地震数据与测井小层对比"穿线",重新划分高频层序"格架",建立延长组地层"等时"对比方案.该研究有助于延长组油藏分布规律的认识,也为其他陆相湖盆沉积演化和地层等时对比提供了可资借鉴的范例.

The multiple sets of source rocks and crude oil biomarkers in the Yanchang Formation have no clear results of oil-source correlation. Chloroform asphaltenes "A" was extracted from the source rocks and crude oils and microwave digested, and its elemental composition analyzed by ICP-MS for oil-source correlation. The S/P and the ratio of light and heavy rare earth elements are oil-source correlation indices. The total amount of transition metals may be useful for oil-oil and oil-source correlation using cluster analysis techniques, but redox parameters are not effective for oil-oil and oil-source correlation in lacustrine oil. It is proposed that the oils in the Longdong area and Jiyuan area all come from the Chang 7 source rocks. The oils in the Shanbei area are derived from the Chang 9 source rocks in the area and the Chang 7 source rocks in Longdong. The Chang 10 oils in the Shanbei area and Chang 9 oils in the middle Lake Basin appear to come from other sources. Trace elements can provide valuable clue on the hydrocarbon sources and oil migration patterns of the Yanchang Formation, which is of great significance in the search for possible deep oil-bearing systems in the Shanbei area.

The evolution of pore structure in shales is affected by both the thermal evolution of organic matter (OM) and by inorganic diagenesis, resulting in a wide variety of pore structures. This paper examines the OM distribution in lacustrine shales and its influence on pore structure, and describes the process of porosity development. The principal findings are: (i) Three distribution patterns of OM in lacustrine shales are distinguished; laminated continuous distribution, clumped distribution, and stellate scattered distribution. The differences in total organic carbon (TOC) content, free hydrocarbon content (S1), and OM porosity among these distribution patterns are discussed. (ii) Porosity is negatively correlated with TOC and plagioclase content and positively correlated with quartz, dolomite, and clay mineral content. (iii) Pore evolution in lacustrine shales is characterized by a sequence of decreasing-increasing-decreasing porosity, followed by continuously increasing porosity until a relatively stable condition is reached. (iv) A new model for evaluating porosity in lacustrine shales is proposed. Using this model, the organic and inorganic porosity of shales in the Permian Lucaogou Formation are calculated to be 2.5%–5% and 1%–6.3%, respectively, which correlate closely with measured data. These findings may provide a scientific basis and technical support for the sweet spotting in lacustrine shales in China.

In situ conversion is a process that converts organic matter into light oil and gas via underground in situ heating, which leads to changes in shale material composition and dynamic changes in thermal field parameters. At present, there is a lack of understanding of the evolution behavior and mechanism associated with dynamic thermal field parameters of shale. The dynamic thermal field parameters of shale with different organic matter abundances at various temperatures, orientation, heating rates, and pressures are obtained using an improved surface thermal source method and the laser flash method. The results show that the changes in dynamic thermal field parameters of shale are mainly controlled by organic matter abundance. The thermal diffusivity of shale decreases with the increase in temperature, and the thermal conductivity presents an "M-shaped" dynamic evolution with temperature. The thermal conductivity and thermal diffusivity of shale parallel to bedding are higher than those shale that are perpendicular to bedding. The rapid heating rate decreases thermal diffusivity above 200 degrees C, which is believed to be due to the instantaneous weight loss rate at high temperatures. The thermal conductivity and thermal diffusivity of shale parallel and perpendicular to bedding show the following two-stage evolution characteristics with the increase in pressure. Through matrix analysis, the bi-directional thermal conductivity model of shale with different organic matter abundances under different temperature and pressure conditions is constructed, which provides accurate parameters for studying dynamic thermal field evolution and efficient heat transfer during in situ conversion.

With shale oil becoming an increasingly important resource in global oil and gas exploration and development, the breakthrough pressure of crude oil in shale series source rocks has become an important topic for research on hydrocarbon migration. Shale has long been recognized as an effective source and cap rock, with, up to now, the most common method used for breakthrough pressure testing in shale being the gas method. However, this paper sets out a new system for testing the breakthrough pressure of crude oil in siltstone, mudstone, and shale based on differences in electrical resistance between crude oil and formation water. The breakthrough pressure of crude oil with different lithology was tested in different directions using this method. The results show that breakthrough pressure anisotropy can be observed in mudstone, shale, and siltstone, and that the breakthrough pressure parallel to the bedding direction is one fourth or one seventh of the breakthrough pressure perpendicular to the bedding direction. The horizontal breakthrough pressure of shale is one twentieth to one third of that of mudstone and siltstone, and the vertical breakthrough pressure of siltstone is one seventh of that of mudstone and shale. The breakthrough pressure anisotropy of crude oil reveals that the main migration direction in shale series source rocks is in the direction of bedding unless faults or fractures are encountered. The main migration channels in shale series source rocks are in the horizontal direction, and hydrocarbon migration occurs more easily in laminar shale than in mudstone. Horizontal migration is also the principal mode of hydrocarbon expulsion in thick mudstone and shale. The breakthrough pressure experiments on crude oil in this study also reveal the migration directions and modes in intra-source rocks. This improves on the existing oil migration model and has great significance for understanding the migration of oil in shale source rocks.

页岩油地下原位转化技术的应用是实现中低成熟度页岩油规模开发利用的有效手段,加热过程中页岩的热膨胀研究对于井眼稳定性、加热器寿命以及盖层完整性等工程评价具有重要意义.选取鄂尔多斯盆地三叠系长7页岩段3口取心井的岩心,在常规镜下薄片观察、X射线衍射分析基础上,采用DIL402 SE型热膨胀仪获得25～600℃下泥质粉砂岩、泥岩和黑色页岩的热膨胀系数及其动态演化特征.研究结果表明:①鄂尔多斯盆地三叠系长7富有机质段不同岩性的热膨胀系数存在较大差异,并随有机碳含量(TOC)的升高而增大.当TOC值小于5％时,岩石热膨胀系数"近指数型"增大;当TOC值大于等于5％时,岩石热膨胀系数呈"四段式"复杂变化.②研究区富有机质页岩的热膨胀系数各向异性因子最大,垂直层理方向上是平行层理方向上的1.7～2.7倍.③富有机质页岩生烃强度大,能产生微裂缝并导致热膨胀复杂变化.

The Chang 9-Chang 10 Formation in the Ordos Basin has been explored intensively in recent years. However, the accumulation timing and migration paths of the oil in the formation reservoir are still unclear. This study uses reservoir geochemistry and software basin modeling to study the hydrocarbon accumulation periods of the oilbearing sandstones in four wells in different areas of the basin. The results show that the principal oil charging period of the Chang 9-Chang10 formation was from 100 Ma - 130 Ma. The Chang 10 oil reservoirs in the Shanbei area and the Chang 9 oil reservoirs in the Jiyuan and Longdong areas experienced a single oil charging period. However, the Chang 9 oil reservoirs in the central lake area experienced two oil charging periods, from 190 Ma - 210 Ma and from 100 Ma - 130 Ma. The relative abundances of 1,8-/2,7-Dimethylcarbazole and PSNs/Ens carbazole indicate that there are hydrocarbon charging points in the source rocks of the Chang 7 formation in the Jiyuan area, and charging points of Chang 9 source rocks in the Shanbei area. Chang 9 crude oil in the Longdong area shows the characteristics of long distance migration. This study improves understanding of the hydrocarbon accumulation process in the Chang 9-Chang 10 oil reservoirs, which will inform and support future oil and gas exploration in the area.

Major breakthroughs of shale oil exploration have been made recently in the upper member of Paleogene Lower Ganchaigou Formation of Yingxiongling area,Qaidam Basin.However,the low total organic carbon content of saline-lacustrine source rock,and unclear genetic mechanism,evaluation criteria and resources potential of the shale oil have restricted the explo-ration and evaluation of Yingxiongling shale oil.Through analysis of large amounts of cores,well drilling,seismic,laboratory test data and integrated study,focusing on the shale and mixed types of shale oil reservoirs characterized by high-frequency interbedded organic-rich laminated shale and limy dolomite,it is concluded that the shale oil in the upper member of Lower Ganchaigou Formation in the Yingxiongling area have six geological characteristics:(1)two-stage hydrocarbon generation of hydrogen-rich source rock and large amount of retained oil;(2)multiple types of reservoir space and good reservoir properties;(3)source-reservoir integration,thick"sweet spot"and high oil-bearing grade;(4)high pressure coefficient between and under salt layers,and sufficient formation energy;(5)high content of light components,high gas-oil ratio,and good quality of the crude oil;(6)high content of brittle minerals and good fracability.The evaluation criterion of shale oil is preliminarily established based on the eight parameters:total organic carbon content,maturity,effective porosity,oil saturation,brittle mineral content,pressure coefficient,lamellation density,and burial depth.Combined with parameters of E32 source rock thickness,area,vertical distribution of oil layers,and free hydrocarbon content,the shale oil resources have been preliminarily estimated as 21×108t.The structurally stable area is the predominant objective of shale oil exploration and the favorable exploration area for Yingx-iongling shale oil is nearly 800 km2.

Based on core observations, the microheterogeneity, diagenetic features, diagenetic mineral compositions, and stable isotopes of cements in the calcareous interlayers in the Donghe sandstone were studied by polarizing microscopy, cathodoluminescence microscopy, X-ray diffractometry, isotope ratio mass spectrometry, and other techniques. By determining the proportions of cements of two phases by a statistical method and their clumped isotope values by an end-member method, the multiphase calcareous cementation was shown to be the major contributor to densification. Cluster isotopes revealed that the average formation temperatures of calcareous cements in phases II and III of cementation were 45–50°C and 80–90°C, indicating that they were products of the A and B phases during early diagenesis, respectively. According to the homogenization temperatures of coeval salt-water inclusions associated with hydrocarbon inclusions, which range from 100°C to 130°C, basin modeling revealed that the basin underwent mainly one stage of hydrocarbon charging during 8–5 Ma in the Miocene period. The cements of the two phases in the oil-free calcareous interlayers in the Donghe sandstone, which are the main controlling factor of the oil-water distribution in the reservoir at present, formed much earlier than the oil filling in the oil-bearing sandstone.

The CO2 sequestration and enhanced gas recovery (CS-EGR) technology provides a very effective way to alleviate the greenhouse effect and energy crisis. The characteristics and mechanisms of CO2/CH4 competitive adsorption in shale matrix as well as the effects of reservoir parameters play a vital role in enhancing shale gas production and CO2 storage. However, it has not been fully understood especially in pores with heterogeneous surfaces composed of organic matter and inorganic compounds. A graphene-MMT heterogeneous surface was proposed as a pore model and molecular dynamics (MD) simulations have been applied. Absolute adsorption selectivity based on the fixed mole fractions of CO2 and CH4 in the total shale pores has been proposed to evaluate the competitive adsorption features with relative adsorption selectivity. A strong asymmetric competitive adsorption behavior of CO2 and CH4 has been observed. The competitive adsorption behavior near the MMT surface lags behind that near the graphene surface, especially in 3 similar to 8 nm pores. The influence mechanism of pore size on competitive adsorption is believed to be the confinement effect of the pore leads to the competition for the gas source in the pore between the heterogeneous surfaces. The confinement effect near the graphene surface is obvious when the pore size is smaller than a critical pore size of 6 nm. In addition, the confinement effect of CO2 in pores with heterogeneous surfaces is more obvious than that of CH4. Based on absolute and relative adsorption selectivity, it's reasonable to control the average pore size around 12 nm during cracking process, and the pressure may be chosen as low as possible within the proper range obtained based on the absolute adsorption selectivity.

Based on 991 groups of analysis data of shale samples from the Lower Member of the Cretaceous Eagle Ford Formation of 1317 production wells and 72 systematic coring wells in the U.S. Gulf Basin, the estimated ultimate recovery (EUR) of shale oil and gas of the wells are predicted by using two classical EUR estimation models, and the average values predicted excluding the effect of engineering factors are taken as the final EUR. Key geological factors controlling EUR of shale oil and gas are fully investigated. The reservoir capacity, resources, flow capacity and fracability are the four key geological parameters controlling EUR. The storage capacity of shale oil and gas is directly controlled by total porosity and hydrocarbon-bearing porosity, and indirectly controlled by total organic carbon (TOC) and vitrinite reflectance (Ro). The resources of shale oil and gas are controlled by hydrocarbon-bearing porosity and effective shale thickness etc. The flow capacity of shale oil and gas is controlled by effective permeability, crude oil density, gas-oil ratio, condensate oil-gas ratio, formation pressure gradient, and Ro. The fracability of shale is directly controlled by brittleness index, and indirectly controlled by clay content in volume. EUR of shale oil and gas is controlled by six geological parameters: it is positively correlated with effective shale thickness, TOC and fracture porosity, negatively correlated with clay content in volume, and increases firstly and then decreases with the rise of Ro and formation pressure gradient. Under the present upper limit of horizontal well fracturing effective thickness of 65 m and the lower limit of EUR of 3×104 m3, when TOC<2.3%, or Ro<0.85%, or clay content in volume larger than 25%, and fractures and micro-fractures aren't developed, favorable areas of shale oil and gas hardly occur.