In order to study the lithology, property and brittleness of Gulong shale reservoir, a whole-section coring well, Well-GY8HC, is deployed in Gulong Sag. Detailed core description and element analysis show that the sedimentary microfacies in Gulong Sag are mainly semi-deep to deep lacustrine facies during the sedimentary period of Q1 to Q9 reservoirs, with thick organic-rich shale developed and can be subdivided into four types of lithology which are shale, siltstone, shell limestone and dolomite. Based on the classification principle of “structure+lithology” and combined with the lithology content characteristics, the lithofacies are divided into four types which are laminated shale, intercalated shale, massive dolomite and massive siltstone. The paleo-sedimentary environment is fresh water-brackish water+weak provenance+strong reduction in warm and humid climate, providing favorable place for organic matter formation and preservation. Comprehensive evaluation of three indexes of reservoir capacity, oil-bearing property and fracability shows that several reservoir space types of Q1 to Q3 reservoirs with good physical property, excellent oil bearing property and efficient fracability for shale oil production, being the most favorable interval for medium and high mature shale oil exploration in Daqing Oilfield.

As a systematic study of the Wufeng-Longmaxi Formation was carried out by paleontological comparison, thin section identification, scanning electron microscopy and Nitrogen Adsorption Method in Qilong Village outcrop, Xishui, Guizhou Province, the following main insights are obtained: ① The Wufeng-Longmaxi Formation in Qilong Village outcrop is complete, and is conformable with overlying Silurian Shiniulan Formation and the underlying Ordovician Jiancaogou Formation, with 12 graptolite biozones developed and without unconformity; ② Based on a variety of sedimentary fabric features, six major shale lithofacies in the Wufeng-Longmaxi Formation are determined; ③ The quartz content of the Wufeng Longmaxi Formation decreases, while clay minerals increase gradually from the bottom to the top in Qilong Village outcrop, which shows the content of brittle minerals decreases, and a decrease of fracability of the shale from the bottom to the top; ④ The organic matter types of Wufeng-Longmaxi Formation in Qilong Village outcrop are mainly of type Ⅰ and type Ⅱ₁, and the high TOC shale is mainly distributed in the Wufeng and lower Longmaxi Formation; ⑤ There is relatively low paleoproductivity of the Wufeng-Longmaxi Formation in Qilong Village outcrop. The high quality black shale was deposited in anoxic-dysoxic conditions, and high content of organic matter benefits from the high burial efficiency of organic matter; ⑥ The organic pores of the Wufeng-Longmaxi Formation in Qilong Village outcrop are mainly distributed in Wufeng and lower Longmaxi Formation, while organic pores were not developed in the upper member of Longmaxi Formation or Guanyinqiao member. The abundance of the small pores vertically decreases with stratigraphy upwards and The abundance of the large pore increases with stratigraphy upwards; ⑦ The natural gas adsorption capacity of the Wufeng-Longmaxi Formation in Qilong Village outcrop is a minimum of 1.62 m³/t, a maximum of 2.8 m³/t, and an average value of 2.13 m³/t. This shows that the larger the TOC value is, the stronger the corresponding adsorption capacity will be, and indicates organic matter content plays a decisive role in gas-bearing capacity of organic-rich shales.

In China, shales are widely distributed, continuous in time and complex in space. In this paper, the distribution of shales in the North China, South China and Tarim Plates are systematically sorted out and discussed. The Middle and Upper Proterozoic shales are dominated by marine facies with some continental facies, of which the littoral-neritic to neritic shelf, marine and continental moraine shales are developed, and the field shale sections are characterized by the distribution on the edges of different paleoplates. The Lower Paleozoic shales are dominated by marine facies, with the development of open shelf to neritic shelf shales, which are mainly distributed in the South China Plate and the Tarim Plate. The Upper Paleozoic shales which are dominated by marine-continental transitional facies and locally by marine and continental facies have the largest development and distribution in China. The Mesozoic and Cenozoic shale types are diverse but dominated by continental facies. The Mesozoic shales are mainly developed longitudinally along Yunnan, Sichuan and Shanxi and latitudinally from Xinjiang to Heilongjiang via Shanxi, while the Cenozoic shales are primarily developed in the eastern and western sides of the North China Plate. The plate margins, fold belts and complex tectonic activity areas exert an important impact on the distribution of shales. The ancient trough has a significant influence on the shale deposition, so do the depositional environment on the shale components, and the components on the weathering resistance of field shale sections. The development of field shale sections in different epochs and regions are affected by multi-factors, and each has specific geological characteristics. Shale in sections can be divided as manganese, siliceous, calcite or dolomite, silty, carbonaceous, coal and mixed types, in which carbonaceous shale can occur in various sections. Manganese shale is primarily developed in the strata before Middle Permian in South China Plate, while siliceous shale is mainly found in the open shelf facies, coal-type shale is developed later and mainly deposited in the marine-continental transitional facies and continental facies, The silty, calcite or dolomite shales are widely distributed. Each type of shale has specific epochal and regional distribution characteristics, so a systematic review of the shale strata in China could be helpful for the discovery for more shale gas in new strata or new areas.

The drilling geological profile of Well-JY1 Wufeng Formation and Longmaxi Formation is the first systematic marine shale gas parameter well profile. The exploration breakthrough of Well-JY1 announces the discovery of Fuling shale gas field, which is named as“Shale Gas Development merit well” by Chongqing Fuling Municipal government. With the drilling geological section in Wufeng-Longmaxi Formation of Well-JY1 as the key point, the drilling profiles of the importance of shale gas exploration and development are expounded, the profile lithostratigraphic, biostratigraphic and graptolite biozone division and fracture development characteristics are introduced, and analyzed the period of “six”shale gas reservoir characteristics and vertical distribution are analyzed. The following conclusion are obtained. Firstly, the Wufeng-Longmaxi Formation in Well-JY1 has large thickness, continuous deposition, clear stratigraphic sequence, widest range of graptolite category and good regional comparability, which can be used as the basic drilling geological section for the analyses and researches of Wufeng-Longmaxi Formation in Sichuan Basin and its surrounding areas. Secondly, affected by sedimentary facies belt, the geological characteristics of different shale gas strata are obviously different. For example, the first interval of the first Member of Wufeng-Longmaxi Formation（small layer ①~⑤）, which belongs to the deep-water shelf facies generally with four high characteristic of “high TOC, high porosity, high air content, high siliceous”, is the main “sweet spot” of the shale gas exploration and development in this area. Thirdly, the small layer ①~③ in high quality shale gas reservoir, which show the high coupling law of double “sweet spot” of geological and engineering, are the optimal layers for the best target “window” of the horizontal wells. Among them, the small layer ② with high gamma value is the best position to ensure the horizontal trajectory and drilling ratio of high quality shale. The determination of high quality shale and the target “window” in deep-water shelf facies is the key for the major breakthrough of shale gas exploration in Wufeng-Longmaxi Formation of Well-JY1 and the continuous stable and high production, and also points out the direction for the selection of the areas and layers during the subsequent shale gas exploration.

In recent years, the exploration of Longmaxi Formation in Sichuan Basin has been successful, but the shale gas of the complex structural belt’s Longmaxi Formation are still the next areas for exploration. Therefore, it is necessary to carry out systematic researches on the Sanbaiti section in Mount Huaying of high-steep structural belt in Sichuan Basin, so as to provide ideas for the further exploration breakthrough. The section’s lithology, paleontology, mineral composition, geochemical characteristics, pore type and structure are studied, and compared with the drilling wells of adjacent areas. The findings are as follows. ①The outcrop in Mount Huaying section is well exposed. The shale strata from Wufeng Formation to the bottom of Longmaxi Formation are complete and continuous. Wufeng Formation is divided into two sections, and the Longmaxi Formation（no top） is divided into three sections. The WF2-LM9 graptolite biozone is well developed. From the bottom to the top, the sedimentary environment changed from reduction to oxidation, and the biogenic siliceous environment has been destroyed. The injection amount of terrigenous debris increases, and the abundance of organic matter shows a downward trend. The organic matter in Long-1 member of Wufeng Formation is relatively rich, and the content of brittle minerals is high. The reservoir space is dominated by organic pores, followed by inorganic pores and microfractures. The pore structure is dominated by ink bottles, and a small amount of slit pores. ②For the Hirnantian-Rhuddanian, although the Sanbaiti section of Mount Huaying is located in the deep-water shelf zone in southern Sichuan, the underwater highland micro-paleogeomorphology is locally developed. Due to the influence of undercurrent and other factors, the deposition thickness of organic-rich shale is thin. So that, the micro-paleogeomorphology has an important influence on the material basis of shale gas formation, which can provide ideas for the further evaluation of Longmaxi Formation. ③The formation of organic-rich shale reservoirs in Long-1 member of Wufeng Formation is mainly controlled by the combined action of volcanism, source supply and reduction environment.

With the comprehensive application of the photography of full thin section, the optical microscope observation of small thin sections, TOC test, whole rocks X-ray composition test, physical property analysis and the observation of field emission scanning electron microscope, Ordovician Wufeng Formation amd Silurian Longmaxi Formation in Shuanghe Outcrop in Changning area are analyzed systematically. The results show that the black shale of Wufeng-Longmaxi Formation in Shuanghe Outcrop of Changning area in southern Sichuan Basin is mainly siliceous shale, calcareous shale and mixed shale, and the average values of quartz, calcium carbonate and clay minerals are 42.5 %, 37.4 % and 14.9 %, respectively, containing a small amount of plagioclase （average 2.5 %）, pyrite （average 2.7 %） and organic matter （average 5.6 %）. The black shale develops mud laminae and silty laminae, and these two types of laminae are composed of five bedding types: graded horizontal bedding, homogeneous bedding, banded silty sand horizontal bedding, sand mud graded horizontal bedding and sand mud thin interbedded horizontal bedding. Progressive horizontal bedding and homogeneity bedding are developed in Wufeng Formation, while strip silty sand horizontal bedding, sand-mud progressive horizontal bedding and sand-mud thin interbedded horizontal bedding are developed in Longmaxi Formation. On the basis of mineral composition and bedding types, eleven types of lithofacies are divided. LM1 member, which is the “sweet spot” interval in Shuanghe Outcrop in Changning area, is characterized by high TOC content, high siliceous content, high porosity, high permeability, high horizontal/vertical permeability ratio and high organic pore content. The strip silty sand horizontal bedding develops here.

In order to explore the characteristics of rich accumulation and the exploration potential of transitional shale gas, the lower Carboniferous shale in southern Guizhou is taken as the research object. Based on the data of two investigation wells and two exploration wells, the analysis is conducted from the aspects of stratigraphic sequence and sedimentary facies, occurrence characteristics of shale, accumulation conditions and favorable area evaluation. The research result shows that: ① The lower Carboniferous shale deposits in western Guizhou are controlled by the NW-SE Shuicheng-Ziyun synsedimentary fault and the Shuicheng-Liuzhi uplift partition, which can be divided into weining shuicheng tidal flat lagoon-transition sedimentary facies and Shuicheng-Ziyun shallow-water shelf marine sedimentary facies, forming Weining and Ziyun depositional central areas with deposition thickness ranging from 30 m to 200 m. The sedimentary thickness of Weining-Shuicheng is 119 m, and the embedded depth of floor is between 1 500 m and 3 000 m, which is a favorable area for exploration. ② Influenced by multi-stage structure and controlled by syndeposition, the gas accumulation type controlled by the combination of folds and faults is relatively developed in this area, which is a typical gas accumulation mode controlled by the structure of anticlinal combination blocked by reverse fault. ③ On the plane, the accumulation zone of Weishui anticline and Shuicheng-Ziyun fault structure is a favorable exploration area for shale gas research in Weining-Shuicheng, the sedimentary center of Jiusi Formation, with an area of about 944 km². There are at least three sets of organic-rich shale gas bearing beds vertically in the shale, which have good exploration potential

At present, the Wufeng-Longmaxi Marine high quality shale is the only case that has been commercially exploited in China. Taking Huangying section in Wulong District, Chongqing as an example, the characteristics of sedimentary geochemistry and their interrelationship of Marine high quality shale are studied by the field observation and field measurement combined with laboratory experiment analysis. The results show that: firstly, the black siliceous shales of Wufeng Formation and dark gray shell argillaceous limestone of Guanyinqiao Formation are exposed from bottom to top in Huangying section, which reflects the sedimentary environment from deep water shelf to shallow sea and then to deep water shelf. Secondly, the biostratigraphy of outcrop layer is continuous and intact, and the Kaidian-Rudan WF2-LM5 graptolite zone can be recognized. The graptolite type, content and preservation characteristics are closely related to the sedimentary environment. Thirdly, the Wulong area is located in the hydrocarbon generation center of the deepwater shelf. The high-quality shale has large thickness, superior static index, high hydrocarbon generation intensity and good material basis for shale gas enrichment. Fourthly, Wulong area is the sweet spot of both shale gas exploration and development because of the good accumulation and enrichment conditions of shale gas in small layer ①—④.

The drilling of Lower Cambrian shale gas in the northern margin of Mount Daba shows good prospect. A set of dark shale strata are generally developed in the lower Cambrian in this area, but the stratigraphic heterogeneity is strong, and the sedimentary facies change obviously in the region. It is helpful for the further exploration and development to the study shale sedimentary characteristics of the Lower Cambrian in this area and analyze its influence on the differential enrichment of organic matter. On the basis of outcrop section in Maoba of Ziyang and experimental data, the researches are carried out from three aspects: the division and correlation of sedimentary facies, the analysis of sedimentary mode and the analysis of favorable sedimentary facies zones. The Lower Cambrian in the study area can be divided into four sedimentary subfacies: sub abyssal rifting trough basin facies, deep water shelf facies, shallow water shelf facies, and platform edge slope facies. Longitudinally, the water body changes from deep to shallow, and the contents of carbonaceous and siliceous gradually decrease, while the contents of clayey and carbonate gradually increase. The dark mud shale developed in the lower Cambrian Lujiaping Formation deep water shelf facies in Langao-Zhenping stratigraphic district has the larger thickness and higher content of total organic carbon and brittle minerals, which is a favorable sedimentary facies belt for the development of high-quality shale.

Detailed field description and experimental analysis have been carried out for Wufeng-Longmaxi Formation shale profile in Anwen Town, Qijiang, Chongqing, by field profile observations and field measurements. Three kinds of lithology formation, namely black siliceous shale of Wufeng Formation, dark gray shell argillaceous limestone of Guanyinqiao and black shale of Longmaxi Formation,are exposed from bottom to top in shale section of Anwen Town. There are three main conclusions. First, the exposed shale is the main formation of current exploration and development, the indicators of reservoir forming conditions are superior, TOC ranges from 1.10 % to 8.10 %, with an average of 3.40 %. The average R_o is 2.70 %; Quartz content ranges from 33.90 % to 56.60 %, with an average of 42.36 %, and clay content ranges from 18.00 % to 57.20 %, with an average of 42.62 %. Second, the main reservoir space types are microfracture, organic pore and inorganic pore. Third, combined with the exploration and development practice, the ①~③ subzone of black shale at the lower part of Wufeng-Longmaxi Formation is the sweet spot section, which is a favorable target of horizontal well.

The upper Ordovician Wufeng Formation and the first member of the lower Silurian Longmaxi Formation are well exposed in Bayu outcrop Daozhen, northern Guizhou, with clear and complete stratigraphic boundaries. Under the control of global sea level changes, the Wufeng Formation and the first member of the Longmaxi Formation develop clay-bearing siliceous shale, siliceous shale, clay-bearing siliceous shale, argillaceous shale and silty shale from bottom to top, which display similar longitudinal superimposition characteristics to the Pengshui area on the edge of the Sichuan Basin and Jiaoshiba area in the basin. Lithology of the organic-rich shale in Wufeng Formation and the first member of the Longmaxi Formation in Bayu outcrop of Daozhen is dominated by clay-bearing siliceous shale and siliceous shale, which have the same organic matter enrichment features as that in the Pengshui and Jiaoshiba area. Specifically, TOC is positively correlated with the content of quartz, and negatively correlated with the content of clay minerals. The total thickness of organic-rich shale in the Wufeng Formation and the first member of the Longmaxi Formation at this profile is 26.1 m, which is lower than that in the Pengshui and the Jiaoshiba area, reflecting a relatively shallow-water depositional environment in the Daozhen area.

The lacustrine mud shale in Jurassic of Sichuan Basin is characterized by fast sedimentary phase transition, complex and diverse lithological combination types, and strong reservoir inhomogeneity, which is quite different from the marine shale. Therefore, it is of great significance to establish a typical geological section of Jurassic lacustrine shale in Sichuan Basin and further study the microfacies and lithologic assemblage characteristics of lacustrine shale. The Da'anzhai section of Fulu Town, Liangping District, Chongqing, Eastern Sichuan is selected as the research object. Through the division of small layers, fine description of sedimentary microfacies and lithologic combination characteristics, sample collection, field profile measurement, organic geochemistry, reservoir physical properties and whole rock X-ray diffraction, it is shown that the Da'anzhai section of Fulu town is mainly carbonate lake sediments. The microfacies and lithologic assemblages have three stages: initial transgression, maximum transgression and initial regression. The first and third members of the Da'anzhai formation are mainly composed of the microfacies of the thick layer mesoclastic limestone deposited in the bioclastic beaches of the carbonate shallow lake; The second member of Da'anzhai formation is a semi deep lacustrine subfacies. There are two microfacies: Storm beach and semi deep lacustrine mud. They are characterized by two lithologic associations, i.e. unequal thickness interbedding of grey clastic limestone and grey black shale, and thick black shale with thin shell limestone, With high content of brittle minerals and better permeability and compressibility, it is a sweet spot for shale oil and gas enrichment. Compared with the typical shale gas drilling, The semi deep lacustrine facies of the second member is mainly distributed in Fuling Jiannan area in eastern Sichuan, which is conducive to the formation of shale oil and gas. The carbonate shallow lacustrine clastic shoals of the first and third members are mainly distributed in Central Sichuan Northeast Sichuan, which is conducive to the enrichment of tight oil and gas.

Taking the shale reservoir as the starting point, Tiansheng standard section is selected as the research object by the survey and optimization of the areas with simple structure, well-developed outcrops, fully developed strata and convenient transportation in Fuling, Nanchuan and Wulong areas. The shale heterogeneity of the outcrop is characterized in the aspect of stratigraphy, mineralogy, petrography, organic geochemistry and storage space, combined with pre-existing seismic, drilling,logging, and laboratory petrophysical and geochemical analyses. The research results show that this section is located in an area of relative stable structure has good horizontal comparability, of which each small layer has typical development characteristics and the thickness changes little. It is a representative and typical observation and research section, which can be used as a reference base for shale scientific research and teaching in Sichuan and Chongqing Region. Meanwhile, it is pointed out that the development of bentonite interlayer has a certain influence on shale quality and shale gas well fracturing. This method of the surface indicating the underground provides a certain guiding significance for the efficient development of shale gas wells.

The oil and gas exploration of the Early Triassic Yinkeng Formation with wide distribution in the Jingxian County of the southern Anhui is relatively lagging. Based on the outcrop, well core and test analysis data, the depositional characteristics, hydrocarbon generation conditions and reservoir conditions of the Yinkeng Formation in southern Anhui are discussed. Using the “UAV stereo photography”, an innovative digital survey of the outcrop can be carried out to extract structural and sedimentary information. Combined with the artificial geology survey and the section digitization of the outcrop, the Yinkeng Formation can be divided into 16 sub-layers. The lithological of Yinkeng Formation is generally consist of gray mud limestone, conglomerate limestone and conglomerate limestone, with black and black gray mudstone. The cumulative thickness of the Yinkeng Formation is 43.8 meters with the TOC content ranging from 0.38 % to 2.21 % and the vitrinite reflectance ranging from 0.95 % to 1.21 %, indicating that the shales of the Yinkeng Formation is good source rocks and has a hydrocarbon potential. The porosity and permeability of limestones in the Yinkeng Formation range from 0.928 % to 2.626 %, and 0.12×10^-3 μm² to 3.22×10^-3 μm², respectively. The limestone intervals have under-developed matrix pores and low permeability, but have developed micro-fractures. Therefore, slopes and open shelf are favorable sedimentary facies with “self-generation and self-storage” petroleum system, and the Yinkeng Formation has large hydrocarbon potential.

With the first discovery of the world's oldest shale gas in Doushantuo Formation of the Lower Sinian in the southern wing of the Huangling anticline, the gas-bearing property of the dark shale has been confirmed. As the main gas-bearing shale bed, the second member of Doushantuo Formation has wide distribution, large sedimentary thickness and good shale quality. Based on the geological survey, and the layers division and characterization of the typical Early Sinian outcrop in Toudingshi Village, Sandouping Town, western Hubei, it is proved that the second member of Doushantuo Formation in this area is a set of dolomitic lithologic assemblage with potential for gas generation. Combined with the core data of the adjacent geological survey Well-ZD-2, the sedimentary characteristics, hydrocarbon generation and reservoir conditions are comprehensively discussed. Results show that the high evolutionary level of the kerogen controls the formation gas content. The adsorbed gas which depends on the Nanometer pores and micro-fractures, is the main component of shale gas in the normal formation pressure.

Based on the abundant core, logging curves, seismic data, sequence stratigraphy, mineralogy, sedimentology and other research methods, the systematic dissection of shales in the upper and lower member of The Fourth and third member of the Shahejie formation in Dongying Sag was carried out by combining macro and micro analysis. The research results show that: ① The mineral composition of shale in saline lacustrine basin is characterized by rich carbonate, and there are mainly high content carbonate shale facies and calcareous shale facies. ② The deep-water shale sequence of the lacustrine rift basin is characterized by inundation unintegrated sequence. The shale section of the Upper Es₄ - Lower Es₃ sub-member in Dongying Sag can be divided into two third-order sequences, four fourth-order sequences （system tracts） and eight fifth-order sequences （parasequence groups）. ③ There is an obvious coupling relationship between shale lithofacies and sequence. The late lacustrine extensional system tract and early high system tract are the favorable stages of high content carbonate shale facies. The research and understanding have certain guiding significance for the division of shale sequence and the prediction of lithofacies distribution in saline lacustrine rift basins.

Well-Ji-174 is an exploration well with the longest core extraction and the most data in the shale oil reservoir of Lucaogou Formation in Jimusar sag, Junggar Basin. The establishment of the “iron pillar” is of great significance to the studies of the shale oil longitudinal characteristics. It is found that the lithology of reservoir is mainly transitional lithology mixed with clastic rock and carbonate rock, and changes quickly in the longitudinal direction. The lithofacies reflects the semi-deep to deep lacustrine sedimentary environment with gradually deepening upward water body. The average porosity and permeability of the reservoir are 11.1 % and 0.056×10^-3 μm², respectively, which make the reservoir presents the characteristics of medium-low porosity, low-permeability and ultra-low permeability. The dolomite and sand content of the reservoir are positively correlated with the physical property and oil content. The upper and lower sweet spots are developed. The main lithology of the upper sweet spot is clastic dolomite, allowing the formation of the reservoir space with developed dissolution pores and a thickness of 24 m. The main lithology of the lower one is fine siltstone, dolomite sandstone and dolomite siltstone, whose reservoir space with thickness of 35 m is mostly fissures and pores. The favorable area of these two sweet spots covers an area of 1 299 km², indicating that the shale oil in Lucaogou Formation has large-scale exploration potential.

Mahu sag is an important hydrocarbon-generating sag in Junggar Basin. The whole well section in Fengcheng Formation of Well-MY1, which is located in the north of the sag, has been continuously coring. Therefore, the coexisting characteristics of conventional and unconventional reservoirs in Fengcheng Formation are revealed by the combination of the systematic description and analysis of core characteristics with the analysis of high-density sampling and electrical/nuclear magnetic resonance. The main conventional reservoirs are volcanic rocks, glutenite and sandstone, which is developed in the low stage freshwater or low salinity water body. The main unconventional reservoirs are mud-stone, dolomite and siltstone, which is developed in the weak hydrodynamic conditions and strong evaporation environment. On this basis, with the comprehensive analysis of lithology, electrical properties, physical properties, oil content and other characteristics, it is further confirmed that there is one conventional “sweet spot” and three unconventional “sweet spot” in Fengcheng Formation of Well-MY1, and the conventional “sweet spot” is developed in the middle and lower part of 1st member of Fengcheng Formation, the unconventional “sweet spot” is developed in the lower part of 3rd member and the 2nd member of Fengcheng Formation. The core analysis and features of Fengcheng Formation in Well-MY1 further confirms the hydrocarbon resource potential of alkali lake deposit, and lays a foundation for the establishment of “Standard Lithology Profile” of Fengcheng Formation in Mahu sag.

The Middle-Upper Permian Gufeng Formation and Dalong Formation are the important target horizons for the source rock exploration in South China. However, due to the obvious lithologic changes in both spatial and temporal distributions, there is still great controversy in the division and comparison of the regional stratigraphy, which restricts the exploration and potential evaluation of oil and gas resources. Thus here we analyzed six typical field outcrops of the Gufeng and Dalong Formations in the Lower Yangtze region and summarized their lithostratigraphic characteristics. By the regional comparison, we further analyzed their vertical and lateral lithofacies distribution. Combined with the geochemical parameters such as total organic carbon（TOC） content, the exploration potential of shale oil and gas is discussed. The results show that the lithological thickness of the Gufeng Formation in the Lower Yangtze region varies greatly, showing the characteristics of alternating thick and thin, and its deposition center is generally located in the areas of Fanchang-Wuhu and Jurong-Lishui. The Gufeng Formation can be basically divided into three members, among which the middle member with interbedded chert and siliceous mudstone is regionally stable and thick. The thickness of the Dalong Formation does not change much regionally, but it is affected by the paleogeographical setting. The lithological differentiation of the Dalong Formation is obvious in the region, and its chert and siliceous mudstone is mainly developed in the southern Anhui area, while in the northern Jiangsu area, it changes to shale. Based on the previous studies, it is suggested that the Gufeng and Dalong Formations of the Lower Yangtze region have high TOC contents, good organic matter types, and their maturity is generally within the gas generation range, indicating that they have great shale gas potential. The vertical distribution characteristics of the TOC in the Gufeng and Dalong Formations indicate that their middle-upper member is a more favorable horizon for shale gas exploration. Regionally, the Wuwei Basin, Jurong-Nanling Basin, Changzhou-Xuanguang Basin and Wuxi-Suzhou area are the relatively favorable areas for shale gas exploration; the Xuanguang-Meishan Basin and the Jurong Danyang-Huangqiao-Taizhou area have shale oil exploration prospects due to their low maturity.

Chang-7 Member in the Triassic Yanchang Formation served as the most important source rock of oil in the Mesozoic Ordos Basin, and it is also the realistic interval for the exploration and development of shale oil. The Chang-7 Member represents the climax depositional period of the Triassic lake basin. It is composed of a set of fine-grained clastic rocks, including mudstone and oil shale etc. The thickness of the Chang-7 Member is 100~120 m, which can be divided into three sub-members. Among them, the Chang-7₁ and Chang-7₂ sub-members have been proved as the key intervals for exploration and development of shale oil. To deepen the understanding of the sedimentary environment and oil and gas geological characteristics of the Chang-7 Member, measurement of the field sections are combined with the previous work. The well-exposed sections of the Chang-7 Member in Yishicun, Beiyincun, Yaoqu, Bawangzhuang and Tangnihe in Tongchuan area are described in detail. Furthermore, the geological background of the formation of hydrocarbon-rich depression in the middle-late Triassic stages is discussed. Our results show, the lake basin went through gradual shrinkage and declining lake level from Chang-7₃ sub-member to Chang-7₁ sub-member, and the sandstone content gradually increase to the upper part. The study area is located in the deep lake area of the Yanchang Formation deposition. The sedimentary types in the Chang-7 Member include not only normal deep-water fine-grained sedimentary rocks, but also diverse deep-water gravity flow deposits, volcanic tuff, and carbonate rocks which might source from hydrothermal fluid in the deep part. These important phenomena record the special process of the formation of the hydrocarbon-rich depression, and have important implications for understanding the hydrocarbon formation and enrichment mechanism, as well as the exploration and development of shale oil.

The Caojiagou section in Qishan County, Shaanxi Province is located in the southern margin of the Ordos Basin. The well-exposed section deposited complete Ordovician strata and developed various sedimentary types, and its location has convenient transportation. In this paper, the stratigraphy and sedimentary characteristics of the Caojiagou section are introduced in detail. The lower Ordovician Yeli Formation is mainly composed of argillaceous dolomite and Mount Liangjia Formation is characterized by crystal dolomite intercalated with siliceous mass and develops stromatolites, all of which belong to tidal flat facies. The Middle Ordovician Majiagou Formation consists of medium-thin and medium-thick layers of silty-fine dolomite and limestone, belonging to open platform and platform front slope facies deposits. The Fengfeng Formation is mainly composed of medium-thin layer laminated dolomite with a great quantity of thin carbonate debris flow and turbidity current deposits, which represent the gravity flow deposit of the front slope of the platform in the deep-water environment. The Upper Ordovician Pingliang Formation mainly consists of a set of flyschoid rhythmic deposits of the continental slope facies. The Tangwangling Formation represents the debris flow environment of the continental slop and develops the ice-water deposits with typical ice-rafted dropstones.

The black shales is widely distributed in Proterozoic Xiamaling Formation of Yanshan area, making the Xiamaling Formation to be an important potential target for shale gas exploration. Field profile survey shows that several sets of diabase sill intruded into Xiamaling Formation, which has great influence on oil and gas accumulation. Therefore, the numerical simulation study on the influence of a set of diabase bed about 7 m thick on the maturity of host rock is carried out based on the measurement of the field section and bitumen reflectance of the neighbouring shales. The results show that the influence range of this diabase bed on R_o of organic matter in host rock is about 8.5 m, which is about 1.2 times of its own thickness. The measured R_o values increases exponentially near the bedrock. The numerical simulation results show that the diabase will cool down almost completely after 110 years, and the disturbance range to the surrounding rock geothermal field is about 100 m, which is much larger than the influence range of R_o. Only when the surrounding rock temperature is greater than or equal to 250 ℃ can it cause the change response of the R_o values. The greater the thickness of diabase bed, the greater the influence range on R_o of organic matter in host rock, and the greater the increase of R_o near the bedrock. The influence range of diabase bed on R_o of organic matter in host rock is about the same to its own thickness.