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The Lower Cambrian Qiongzhusi Formation in Sichuan Basin and on its periphery is rich in shale gas resources, and it has become one of the important shale gas development intervals in Sichuan Basin. Controlled by complex sedimentary setting, the silty shale reservoir in Qiongzhusi Formation has various lithofacies and strong heterogeneity longitudinally, which restricts the exploration and development of shale gas. Therefore, it is urgent to study the sedimentary characteristics, sedimentary facies and sedimentary models. Based on the previous understanding of tectonic setting and sequence stratigraphy, and through detailed analysis of rock data, well logging data, geochemistry data and paleontology data, this paper clarifies the Early Cambrian sedimentary background of combined ocean-paleoland influence, moderate water depth and widespread reduction of Sichuan Basin and its periphery. The paper also believes that the Qiongzhusi Formation is mainly deposited in shore facies and continental shelf facies. The continental shelf facies are dominated, including shallow water continental shelf subfacies and deep water continental shelf subfacies. Based on the analysis of the combined action of wave and tide, seawater evaporation, suspension, rising ocean current, sedimentary paleogeomorphology and other fine-grained sedimentary influencing factors, and combined with the spatial distribution characteristics of sediments, the fine-grained sedimentary model of the Lower Cambrian Qiongzhusi Formation in Sichuan Basin and on its periphery is established, i.e., in the early stage of sedimentation, the effect of differential sedimentation is significant, the sequence thickness varies greatly, and the sedimentary characteristics and influencing factors differ greatly in different regions. In the middle stage of sedimentation, the effect of differential sedimentation is diminished and the difference of sequence thickness decreases continuously. In the late stage of sedimentation, with steady sedimentation, it enters the "open basin" stage, and the sequence thickness tends to be consistent.

As an important biological element, nitrogen is causally linked with organic matter accumulation, but a systematic and regular understanding has not been developed. This paper discusses this issue by taking the widely developed Permian-Paleogene terrestrial (lacustrine) hydrocarbon source rocks in China as an example. The results show that the terrestrial source rocks in China can be classified into three groups according to the nitrogen isotope (δ15N) compositions and combined with the salinity and evaporative alkali mineral characteristics: the circum-neutral group 1 (average δ15N=4.0‰±1.5‰), the circum-neutral group 2 (average δ15N=7.1‰±1.6‰), and the alkaline group (average δ15N=18.4‰±3.3‰). In the circum-neutral group with δ15N < 10‰, the δ15N of the source rocks is positively correlated with organic matter abundance, type, hydrocarbon generating capacity and shale oil potential due to the fact that higher δ15N characterizes changes in the composition of the hydrocarbon generating bio-precursors. In the alkaline group with δ15N>10‰, the organic matter types are good and shale oil potentials are higher, but the response relationship between δ15N of source rocks and organic matter accumulation is not as good as that of the circum-neutral group, reflecting that the organic matter accumulation in alkaline group is influenced by other comprehensive factors other than δ15N. Accordingly, the organic matter accumulation models of three types of lacustrine source rocks (< 5‰, 5‰-10‰, and >10‰) classified on the basis of δ15N were established. The δ15N has the potential to trace organic matter accumulation and quality of source rocks. For example, low δ15N type (δ15N < 5‰) is of poor quality and medium-high δ15N type (δ15N>5‰) is of good qualityin lacustrine source rocks. This paper enriches the biogeochemical and hydrocarbon source rock geochemical studies of nitrogen by exploring organic matter accumulation in source rocks from the new perspective of nitrogen isotope composition and nitrogen cycling.

The Junggar Basin is rich in oil and gas resources, with huge exploration potential, which is one of the main arenas of increasing oil and gas reserve and producing in China. In recent years, CNPC has made major breakthroughs in exploration in the Junggar Basin, revealing the orderly symbionic distribution pattern of conventional and conventional oil and gas. In order to further learn from the oil and gas achievements and exploration and development experience in neighboring areas and the new geological theories, for formulating SINOPEC's oil and gas exploration strategy in the Junggar Basin, the potential and distribution characteristics of the oil and gas resources in the Junggar Basin are systematically analyzed in this paper and it is pointed out that no enough attention is paid to natural gas and unconventional petroleum. The key breakthrough direction and exploration strategy of SINOPEC in the Junggar Basin are put forward in the paper after reviewing the major exploration breakthroughs in multiple fields, multiple strata, and multiple types in recent years and combining with the oil and gas geolo-gical conditions and exploration practice of SINOPEC's mining rights area. The research reveals that the Junggar Basin has entered a new period of exploration dominated by the middle and lower assemblage, and the exploration ideas must be adjusted accordingly. We must insist on the transformation from early outside-source exploration to intra-source and near-source exploration, and from early conventional petroleum exploration to both conventional and unconventional petroleum exploration. In order to make big exploration breakthrough of SINOPEC and realize the target of increasing reserves and production in the near and medium term in the Junggar Basin as soon as possible, four exploration strategies are proposed in the paper, including further figuring out the resources, establishing an integrated research team of conventional and unconventional petroleum, strengthening the joint research of geological and engineering integration, and increasing the support of risk exploration.

Most of the proven undeveloped reserves are presently low-grade ones. Overall effective utilization is difficult with current economic and technical conditions. Most of the existing methods evaluate overall utilization potential, which is no longer suitable for evaluating the utilization potential of currently-proven undeveloped reserves. In this paper, a case study has been carried out in Y reservoir. According to the heterogeneity of the spatial distribution of reservoir parameters, the selectivity of development technology and the uncertainty of economic parameters, a prediction model of single-well-controlled recoverable reserves under different development technologies is built. Combined with the economic limits of single-well-controlled recoverable reserves under different technical and economic conditions, movable probability can be obtained, and the movable potential of geological reserves can be further calculated. Field application shows that the coincidence rate of the movable potential reserves calculated by the method in this paper and the actual produced reserves reaches 97.2%, which has high accuracy and can meet the needs of field. The research in this paper provides an effective method for the evaluation of the potential of undeveloped reserves.

Bedding-parallel lamellated fractures are widely developed in shale in the 7th member of Triassic Yanchang Formation (hereinafter referred to as Chang 7) in the southwestern Ordos Basin, which holds significant importance for sweet spot selection, fracturing operations, and development planning. In this paper, based on the surface outcrop and core observations in the Qingcheng to Huachi region of the southwestern basin, combined with analysis and testing of organic matter content, mineral composition and fabric characteristics, the developmental characteristics of bedding-parallel lamellated fractures in different lithologies in the Chang 7 shale were identified, and the main controlling factors of fracture development were analyzed. Results show that the morphology and distribution of the bedding-parallel lamellated fractures are mainly controlled by the laminates, exhibiting characteristics such as continuous flatness, wavy bending and branching due to the different characteristics of the laminae. Sandstone bedding-parallel lamellated fractures are mostly distributed along the biotite laminae, with good continuity and large aperture, and are generally unfilled. Shale bedding-parallel lamellated fractures are most developed in black shale, mostly distributed along the bedding laminates composed of organic matter layers, with a few partially or completely filled by calcite and organic matter. The aperture is smaller than that of sandstone, but the density is higher. Bedding-parallel lamellated fractures are also controlled by organic matter content, lithology, mineral composition, and laminate structure. The sandstone bedding-parallel lamellated fractures are mainly controlled by the content of biotite and the laminates formed by it. When sandstone sorting is good and biotite content is high with a layered distribution, the degree of fracture development is high. As the density of the laminates increases, the degree of development of bedding-parallel lamellated fractures also increases. Shale bedding-parallel lamellated fractures mainly develop in organic matter laminates and tuffaceous laminates, and are controlled by organic matter content and mineral components. Fracture density increases first and then decreases with the density of the layers. Fracture density in thin laminates is higher than that in thick laminates.

The evaluation of fault sealing is an important part of analyzing hydrocarbon accumulation conditions in fault-block traps. Based on the improved Shale Gouge Ratio (SGR), this paper proposed a new method for evaluating fault sealing, Weighted Shale Gouge Ratio (WSGR). Firstly, the calculation parameters and influencing factors of SGR were analyzed using different geological models, and it is determined that fault distance, mud content, and mud rock distribution are important factors affecting shale smear. It was found that all muddy sediments that slide through the target reservoir have contributions to shale smear within fault distance, but the contributions of different points vary, with higher mud content and closer distances contributing more. Therefore, a new parameter called distance coefficient was introduced to represent the influence of mudstone distribution on shale smear. The distance coefficient is defined as the ratio of the difference between fault distance and the distance from mudstone to the target reservoir to the fault distance. Based on this, a calculation method named Weighted Shale Gouge Ratio (WSGR) was constructed, which is defined as the product of mud content and distance coefficient at each point, summed and divided by the sum of distance coefficients. The sealing performance of known oil and water layers in the upper oil and gas bearing system in the Gaoyou Sag is verified by using Weighted Shale Gouge Ratio (WSGR), and it is considered that when the value of WSGR is greater than 0.6, the fault has good sealing performance, thus determining the sealing discrimination criteria of this method. Finally, good application results have been achieved in the evaluation of fault sealing of Eocene Danan Formation in Yongan and other areas of the Gaoyou Sag.

The sedimentary tuff in the second member of Permian Wujiaping Formation in the northern Fuling area of Chongqing is a new type of organic-rich source rock, which is a new field of unconventional gas reservoir exploration. Clarifying the distribution of key sweet spot parameters of the sedimentary tuff series in the second member of Wujiaping Formation is a primary issue in exploration and evaluation. Based on drilling, logging, experimental analysis and seismic data, this paper evaluated the target sweet spot starting from the sedimentary tuff series' organic geochemistry, lithological characteristics, thickness distribution, formation pressure, fracture development and other geological conditions for reservoir formation and enrichment, and focusing on the two key factors of lithology quality and compressible fracture network. The results show that: (1) The sedimentary tuff series in the second member of Wujiaping Formation in the northern Fuling area is in the deep-water shelf facies, with high organic matter abundance. The TOC content is mainly 5%-6%, the Ro value ranges 1.90%-2.44%, the organic matter types are mainly Ⅰ and Ⅱ, and the thickness of high-quality sedimentary tuff section (TOC≥4%) is 15-20 m, with a wide distribution area. (2) The reservoir space of the high-quality sedimentary tuff section is diversified, the porosity is high, the brittle mineral content is high, the formation pressure coefficient is high to ultra high pressure level, and small-micro fracture zone is developed at the hinge zone, reflecting a good gas exploration potential of "self-generation and self-storage". (3) The sedimentary tuff gas reservoir in the second member of Wujiaping Formation in the northern Fuling area has the laws of high quality control of enrichment, overpressure control of reservoir and fracture network control of sweet spot. The sweet spot evaluation criteria for sedimentary tuff series in the second member of Wujiaping Formation are preliminarily established in combination with the main control factors, and three target sweet spots are selected, with an area of 186.4 km2. The L2-L1 well area in the northwest of the exploration area has good oil and gas shows, which can be a favorable target for recent exploration.

The Bohai Bay Basin is one of the key areas for the exploration of buried hill oil and gas resources in China. In order to create a new prospect for the exploration of the Archaean buried hills in this area, the reservoir-forming laws and main controlling factors of the Archaean buried hill reservoir in the Liaodong Bay area were studied. Based on drilling data such as stratum, logging, and seismic data, this paper classified the lithology and distribution patterns of Archean buried hills in the Liaodong Bay area, and analyzed the dominant reservoir space types and controlling factors. The results show that the Archean buried hills in the Liaodong Bay area are composed of schist, metamorphic granite and cataclastic rocks, with schist being the predominant lithology. The current structure is high in the south and low in the north. The strata are relatively intact in the north, while the upper part of the strata in the south shows evidence of denudation. The proportion of igneous rocks increases gradually from north to south. The metamorphic rocks are dominated by fracture reservoirs. The content of mafic minerals is inversely correlated with the brittleness of rocks. Tectonic deformation led to fracture development. Three sets of structural fractures were developed in the Archean buried hills of the Bohai Bay Basin, i.e., NNE shear fractures and SN tensile fractures were developed in the stress directions of NE strong shear and SN strong compression in the early Yanshanian period, NE shear fractures and NE tensile fractures were developed in the stress directions of NW strong extension and NE weak shear in the early Himalayan period, and EW tensile fractures and NE and NW conjugate shear fractures were developed in the stress directions of NE strong shear and NW weak extension in the late Himalayan period. The degree of regional tectonic activity controlled the effectiveness of the fractures. The Yanshanian movement was the main stage of fracture formation in metamorphic rock reservoirs. During the Himalayan period, fractures were mainly filled and semi-filled with calcite, and effective fractures could be formed through dissolution in the later stage.

The natural gas containing hydrogen sulfide in China has great exploration potential, and the origin, source and formation mechanism of hydrogen sulfide are of concern to petroleum workers. Hydrogen sulfide content and sulfur isotope analysis are two common and important identification indicators. Due to strong toxicity of hydrogen sulfide, many laboratories in China conduct fewer tests or cancel such testing items. In this paper, hydrogen sulfide conversion reagent is preferring selected in pretreatment process. At the same time, through improving isotope mass spectrometer supporting equipment, i.e. tuning the parameters of ion beam focusing of sulfur isotope Faraday cup, installing special chromatography column, Teflon pipeline, sulfur reaction tube, etc., the technology platform for combined measurement of hydrogen sulfide content and sulfur isotope is constructed. Secondly, the high purity sulfur dioxide standard gas is replaced with working standard gas of low concentration, low pressure and small volume, and the optimal experimental conditions are determined through system condition experimental exploration (stability, standard substance analysis, etc.). Finally, the solid precipitate generated by the reaction was sent into the mass spectrometer for the detection of sulfur isotope composition information, and the concentration of hydrogen sulfide in the gas to be measured is calculated by comparing signal with the isotopic composition of standard pure sulfur-containing substances. By using this method, the hydrogen sulfide content and sulfur isotope in some natural gas of Daniudi and Fuxian gas fields in Ordos Basin, and Hongxing area in western Hubei and eastern Chongqing are measured. The measured results are stable with good precision, and are consistent with the results of external laboratories. Comparing traditional method, this method can obtain sulfur content and sulfur isotope values by a single sampling. The preferred silver acetate reagent with one-step chemical method can reduce isotopic fractionation. In addition, the hydrogen sulfide inverting into solid silver sulfide are more reliable directly compared with the standard substance silver sulfide isotope. With low concentration, low pressure, small volume SO2 as the working standard gas, it reduces the laboratory safety risk and instrument damage, and meets the environmental safety requirements.

Shale oil has become the focus of the exploration and development of unconventional oil and gas resources in the world, but its development faces many challenges. Aiming at the complex pore space, the unclear percolation mechanism, and the urgent need to explore research methods of shale oil, this paper systematically expounded the research status of microscopic percolation mechanism of shale oil in experimental methods and computational simulation, and discussed the existing problems and the development trend of future research from the perspective of pore-scale and core-scale. The results show that the combination of various experimental methods can well characterize the pore structure of shale, but the characterization of micro-scale and core-scale flow is still insufficient. The direct method represented by Lattice Boltzmann Method and the indirect method represented by pore network simulation are the main methods to study pore-scale flow mechanism, but the consideration of micro-scale effect needs to be improved. The study of core-scale flow mechanism is mainly to establish a percolation model considering boundary layer effect based on capillary bundle model and fractal theory. It is pointed out that the main future research direction is to fully consider the factors such as boundary adsorption/slip, density/viscosity heterogeneity, stress sensitivity, start-up pressure gradient of shale oil in micro-nano pores, realize multi-scale percolation mechanism coupling, and establish a mathematical model that can accurately characterize the multi-phase and multi-scale flow of shale oil.

Compared with the exploration and development of medium-shallow shale gas, deep shale gas is deeply buried, with complex structures and variable pressure systems, making it difficult to increase drilling speed. The reservoirs are of poor compressibility and it is difficult to transform the volume. How to improve drilling and completion efficiency and reduce drilling and completion costs is the largest challenge in achieving the economic benefits of deep shale gas development. In order to clarify the current technical level and existing problems of deep normal pressure shale gas drilling and completion, the technical indicators and progress of deep shale gas in drilling and completion engineering at home and abroad are summarized and analyzed in this paper and it points out the existing problems and puts forward suggestions. SINOPEC has realized the economic benefit development of deep normal pressure shale gas in blocks such as Weirong and Yongchuan and has basically formed a high-efficiency drilling technology system for long horizontal wells with low-cost high-performance oil-based drilling fluid, enhanced drilling parameters, high-torque positive displacement motor, personalized drill bit, precise guidance and efficient control of long horizontal wells, real-time drilling monitoring and intelligent optimization technology as the core. The maximum horizontal section length and one-trip footage have been extended to 4 386 m and 4 225 m respectively. However, compared with the advanced records in North America, there is still a certain gap between the life of positive displacement motor, stability and reliability of rotary steering tools, super one-trip drilling technology and ratio, and near-bit push tools. Therefore, it is necessary to research and develop the core tools to further improve the drilling efficiency. Due to the limitation of economic development benefits, the deve-lopment of deep shale gas in North America is less than 4 200 m. In China, we have broken through the 4 700 m deep shale gas fracturing technology and formed an independent 4 700 m deep shale gas fracturing technology system with fracturing technology, segmented tools, main materials, and monitoring technology as the core. However, for deep and ultra-deep shale in complex structural areas, it is difficult to form complex fracture nets. It is extremely necessary to further improve the fracture propagation mechanism, develop a fracturing fluid system with better drag reduction and 175 MPa fracturing equipment to break through the bottleneck of efficient fracturing technology for 4 700-6 000 m shale gas.

The relationship between fractures and gas logging in Nanchuan-Wulong area in eastern Sichuan Basin is utilized to study the identification of fractures in shale gas horizontal wells based on geological (core), imaging logging, logging evaluation, seismic prediction, and other data. First, to solve the problems of lack of core and imaging logging and difficulty in identifying natural fractures in shale gas horizontal wells, a core scale shale natural-fracture identification model is established through vertical wells from a geological perspective in this paper, and the development of high angle fractures in the core is consistent with the high values and peaks of total hydrocarbon anomalies. Second, in combination with the fracture identification mode, the fracture development section of non-coring vertical wells can be quickly and qualitatively identified at a low cost based on total hydrocarbon information. There will be a sudden increase in the total hydrocarbon value in the fracture development section, especially in the shale section with low total organic carbon (TOC). The sudden increase in the total hydrocarbon value also represents the existence of fractures. Finally, the plate method of TOC and normalized total hydrocarbon correlation is used to quantitatively identify vertical and horizontal well fracture sections without coring and imaging logging data. The area delineated by a normalized total hydrocarbon value ≥0.4 and TOC ≥0.5% are considered as the fracture development section of a horizontal well. Based on the identified horizontal well fracture section, from the perspective of geological engineering integration, it is possible to avoid or pay attention to these densely developed large or giant fractures in advance, thereby increasing the production of a single well.

Deep shale gas is an important research direction for increasing shale gas storage and production in the Longmaxi Formation of Sichuan Basin. But there are differences in reservoir and seepage characteristics between shallow and medium-buried shale gas, which to some extent limits the progress of exploration and development of deep shale gas. In order to clarify the pore structure characteristics of deep shale gas reservoirs and the transport characteristics of shale free gas, this paper takes the high-quality shale of Longmaxi Formation in southern Sichuan as an example to carry out experiments on observing and quantitatively characterizing the pore structure of shale reservoirs. In addition, based on the transport mechanism of bulk gas, the transport characteristics, critical conditions, and dynamic evolution laws of shale free gas were explored. The experimental and computational results indicate that: (1) The pore morphology characteristics of deep shale reservoirs are not significantly different from those of shallow and medium-buried shale, but the pore structure characteristics of medium pores are more obvious, with pore volume accounting for 62.5%-69.7%; (2) The transport modes of deep shale free gas are divided into three types: transitional flow, slippage flow, and Darcy flow. The critical pore sizes of the three modes in the Yongchuan area are 4.2 nm and 420 nm, respectively. On this basis, a transport chart for free gas in the entire basin has been established; (3) From shallow to deep shale, the critical pore size corresponding to different transport modes of free gas decreases accordingly. The main transport mode of free gas changes from the transitional flow (up to 63.0%) to the slippage flow (up to 67.3%) and the Darcy flow accounts for no more than 2%. The transport capacity of free gas rapidly decreases from shallow to medium-buried shale, while the transport capacity of medium to deep shale free gas remains basically stable with increasing burial depth. By analyzing and comparing the pore structure characteristics and free gas transport characteristics of deep and shallow shale reservoirs, this study can effectively support the deployment of efficient exploration and development plans for deep shale gas and even shallow shale gas in the next step.

In recent years, while actively promoting the development and adjustment of high-pressure shale gas reservoirs such as Jiaoshiba shale gas reservoir, Fuling shale gas field has steadily expanded its development targets to Baima block and other complex structural blocks in order to ensure continuous and stable production capacity. Based on the strong structural deformation, complex geological conditions, low single-well productivity, and great development difficulty of Baima block, this paper deeply studies the tectonic deformation stages, stress field distribution characteristics, favorable targets, and development technical countermeasures of Baima block by means of fracture zone calcite U-Pb dating, three-dimensional stress field modeling, geoengineering integration evaluation and other technical methods, and has made positive progress: it is suggested that the thrust nappe force is the main controlling factor of the deformation difference of marine normal pressure shale gas reservoirs in Fuling area; the evaluation parameter system of "two categories, six items" for development area selection is established, and the south of Baima syncline core is identified as the most favorable target for beneficial development; a differentiated development technology policy based on the development characteristics of natural fractures has been formed; the engineering process countermeasures based on different geological characteristics such as gas well buried depth, stress property and crack are formed. On the basis of the above understanding, and in accordance with the idea of "overall deployment, evaluation-construction integration, and platform replacement", 30 development well locations were deployed and implemented in 2021-2022, the average ROP was increased by 38%, the fracturing rate was increased by 2-3 times, the single stage fracturing cost was reduced to 850 000 yuan, the daily gas output was stable at 800 000 square meters, and the annual gas output reached 224 million square meters in 2022, basically realizing beneficial development.

Strike-slip faults and their related structures have great value for oil and gas exploration. Accurate understanding of the evolution degree of strike-slip faults is crucial to oil and gas exploration in strike-slip structural belts. Previous studies have had a qualitative understanding of the growth and evolution process of strike-slip faults, but there is still a lack of objective and quantitative basis to determine the evolution degree of strike-slip fault zone. The key is the lack of parameters that can characterize the evolution degree of strike-slip faults. In order to solve this problem, this paper, based on the independent physical simulation experiment of Riedel shear structure, collected plane images and carried out a statistical analysis of fault geometry parameters in strike-slip fault zone. By analyzing the corresponding relationship between the periodic change of plane structure and the change of geometric statistical parameters during the evolution of fault zone, the change law of geometric parameters during the evolution of fault zone is revealed, and a new understanding is proposed that the standard deviation of the angle data between adjacent faults in the same fault zone is taken as the characterization parameter of the evolution degree of strike-slip faults. The main conclusions are as follows: (1) The evolution degree of strike-slip fault zone is significantly related with the standard deviation of the angle data between adjacent faults in fault zone, and the plane structural style in different evolution degrees corresponds to the distribution interval of the standard deviation of the angle data between adjacent faults in fault zone; (2) According to the combination pattern of fault planes, the evolution stage of strike slip fault can be divided into shear unidirectional fracture stage, shear en echelon fracture stage, and shear connected fracture stage, and the corresponding standard deviation (S) of the angle data between adjacent faults in fault zone is 1 < S < 4, 4≤S < 8, and S≥8, respectively; (3) For the actual strike-slip fault zone, the evolution degree of strike-slip faults can be revealed by statistical analysis of the standard deviation of the angle data between adjacent faults in fault zone.

Oil and gas resources are of important strategic importance for China's economic development. After more than 50 years of mining in main oil fields, the water cut of oil fields in China has exceeded 90%. China's external dependence on oil and natural gas has increased from 58.9% and 29.2% in 2013 to 71.2% and 40.2% in 2022 respectively, reaching the oil security warning line and impeding national security. In order to find more replacement reserves, oil and gas exploration has been promoted to the "deeper and more complicated" ultra-deep exploration area of 10 000-meter depth. Recently, domestic oil companies have successively implemented the "Deep Sea No. 1" and "Deep Earth No. 1" oil and gas exploration plans, which have explored and practiced new technologies of intelligent drilling and promoted the implementation of the 10 000-meter exploration plans, and reservoirs have been encountered by wells over 9 000 m deep. Based on recent exploration practice, this paper demonstrates the basis of petroleum geological theory for exploration of 10 000-meter depth from the aspects of ultra-deep hydrocarbon generation, storage and accumulation mechanisms, and it suggests that multi-source hydrocarbon generation can be identified in ultra-deep strata and the hydrocarbon generation threshold has exceeded 120-160 ℃. The "three-element controlling reservoir" theory points out that deep and ultra-deep reservoirs can be developed at depths greater than 4 500 meters and multi-phase hydrocarbon accumulation and preservation constitute a favorable condition for the development of ultra-deep large-scale oil and gas reservoirs. The Sichuan Basin has the total resources of about 15.22×1012 m3 in deep marine strata, wherein the Sinian system on the margin of Mianyang-Changning taphrogenic trough, the Longwangmiao Formation on the margin of central Sichuan palaeo-uplift, the Longwangmiao Formation in Micang Mountain-Daba Mountain areas to the east of Chengkou oceanic trough, and the Upper Paleozoic in western Sichuan have a resource potential of more than hundreds of billions of cubic meters. The Tarim Basin has about 15.262×109 tons of equivalent oil in deep marine strata, wherein the Middle-Lower Ordovician karst area in the Tabei uplift, Tazhong uplift and Maigaiti slope, the Middle-Lower Cambrian platform marginal zone on the western margin of Manjiaer Sag, and the Middle and Lower Cambrian intraplatform shoal of Awat-Shuntuoguole are all oil potential areas of hundreds of millions of tons. There are important oil and gas discovery in the Middle Neoproterozoic in the southwest edge of Ordos Basin. Additionally, the field of clastic rocks such as the deep strata in the central deep depression zone in Junggar Basin and the Kuqa Depression in Tarim Basin are also important areas of exploration of 10 000-meter depth.

Organic matter pores is the most important shale reservoir space in South China, and the types of organic matter influence the formation and evolution process of organic matter pores. In order to achieve in-situ observation of the pore evolution process of single organic matter and reveal the pore evolution process during the pyrolysis of the macerals of the Lower Paleozoic shale, this paper focuses on the low-maturity Upper Ordovician shale from Ohio, USA and the Lower Silurian shale in the eastern Baltic Sea, Europe. By using femtosecond laser, cooling-heating stage, microscope and SEM techniques, the in-situ observation of pore evolution of the single organic matters in shale can be realized, and the pore development process and evolution law of different types of organic matters can be distinguished. The in-situ observation results of pore thermal evolution process of low-maturity "gas-prone" graptolite and "oil-prone" lamalginite show that: (1) The initial temperature of obvious volume change of graptolite is higher than that of lamalginite, which infers that the hydrocarbon generation of graptolite is later than that of lamalginite. (2) Both graptolite and lamalginite generated obvious shrinkage cracks during thermal evolution process, but the scale of shrinkage cracks of graptolite is smaller than that of lamalginite, indicating that the hydrocarbon-generating transformation ratio of graptolite is lower than that of lamalginite. (3) There is an obvious difference between graptolite and lamalginite in the evolution of internal pores: the intrinsical biopores of graptolite were enlarged and some new internal pores were formed during the high temperature stage, but no new internal pores of lamalginite were observed during the whole process of thermal evolution, which infers that "gas-generating window" is the main stage of organic matter pore development. Moreover, the difference in the composition and structure of organic matters may be the main reason for the difference in pore evolution of graptolite and lamalginite.

Traditional carbonate rock slice identification is based on manual observation and description, which is highly subjective, mainly qualitative and difficult to quantify. In this paper, an intelligent rock thin-section image information mining model covering the process and technology is designed. The mapping relationship between lithofacies characteristics and thin slice images is constructed through a petrographic analysis framework. A full-flow feature extraction algorithm is also designed by combing image processing and deep learning. Qualitative recognition of grain type in structural component features is obtained by convolutional neural network, that is, the classification of grains (intraclasts, bioclasts, envelopes, spherulites and agglomerates) based on the improved ResNet50 model. Quantitative recognition of grain content, size, shape and contact mode in structural component features are obtained by digital image processing, that is, grain content is calculated based on threshold segmentation, grain morphology parameters are calculated based on minimum peripheral circle/minimum peripheral rectangle and by combining with area ratio/aspect ratio, intersection ratio (IoU) and other algorithms. And the qualitative and quantitative identification of calcite and other minerals in mineral component features are obtained by HSV colour space processing of the stained images. A thin section example from Shun X well is given as an example, and the validity of each feature extraction algorithm is verified through the complete image recognition process and comparison with the manual identification report. The results show that the petrographic analysis framework is effective in representing meaningful information in sparry grain limestone. Through the model of combing petrographic analysis framework with image analysis algorithm, a standard and intelligent identification of this type of carbonate rocks has been achieved, which can provide effective method support for the study of intelligent identification of rock slice images.

In order to gain a deeper understanding of the pressure relief characteristics of shale brittle fracture caused by large-scale tectonic uplift and its impact on shale oil enrichment, this paper, taking the Chang 73 sub-member of Yanchang Formation in Yan'an area of Ordos Basin as the research object, quantitatively analyzes the evolution of different lithological properties from overpressure to underpressure or near normal pressure, and further summarizes its influence on the enrichment of shale oil by utilizing the modified overpressure identification plate and numerical simulation techniques and taking into account the effects of temperature reduction, elastic rebound, and brittle rupture of overpressured shale in the process of tectonic uplift. The results show that the origins of overpressure at the end of the Early Cretaceous in the Chang 73 sub-member in the study area are mainly hydrocarbon generation and disequilibrium compaction, and the overpressure of the sandstone layer mainly originates from the overpressure transference from the neighboring source rocks; elastic rebound and temperature reduction due to tectonic uplift since the Late Cretaceous dominates the formation of underpressure in the Chang 73 sub-member sandstones in the study area, and brittle fracture pressure relief and temperature reduction lead to the formation of weak overpressure or near normal pressure in the Chang 73 sub-member shale. The timing of brittle fracture pressure relief of the top and bottom sets of organic-rich shale in the Chang 73 sub-member of the study area is not synchronized, resulting in large transport dynamics (source-reservoir excess pressure difference) between the top and bottom sets of organic-rich shale and their intercalated sandstones with magnitudes ranging from 16 to 22 MPa. Meanwhile, fractures in the top shale have closed during oil and gas preservation, and there is an excess pressure differential of about 1.42-6.80 MPa between it and the underlying sandstone, which strengthens the hydrocarbon containment capacity of the shale. Differential evolution of formation pressure under different source-reservoir configurations plays an important role in controlling shale oil enrichment.

In order to accelerate the exploration and development of shale gas, this paper elaborates on the micro mechanism of shale gas preservation based on shale self-sealing. The self-sealing capacity of shale formations is mainly related to the low connectivity of nano-throats, low speed diffusion caused by bound water occurrence, capillary force sealing, and breakthrough pressure along the layer direction under burial conditions. Results of analysis based on shale pore morphology and connectivity show that the organic pores in shale are mainly composed of nano-throats with poor connectivity and significant retention effects. At the same time, the stacking of multiple relatively dense sealing layers within the top, bottom, and shale layers is conducive to self-sealing in longitudinal direction. Based on experimental and molecular dynamics simulation analysis of the influence of bound water on the diffusion and breakthrough pressure of the shale matrix, it is revealed that the bound water occurrence significantly reduces the effective diffusion capacity of shale matrix pores and could cause high capillary forces, leading to effective sealing of the gas stored in organic pores. In the study, the permeability-breakthrough pressure evolution relationship was constructed, revealing that under deep burial conditions, the effective closure of shale bedding fractures along the layer direction can form high breakthrough pressure sealing. During the uplift stage, under relatively weak tectonic compression, the shale could still maintain a high sealing capacity along the layer direction, which is conducive to shale gas preservation. However, under strong tectonic compression, the shale bedding fractures open and communicate with open fault surface, causing the failure of preservation capacity and large-scale loss of shale gas. This study elucidates the microscopic mechanism of shale gas preservation through experiments and molecular dynamics simulations, which could provide useful guidance for marine shale gas exploration in complex structural areas.

The study of thermal history of sedimentary basins is very important for oil-gas accumulation analysis and has decisive influence on oil and gas exploration and oil-gas resource evaluation. However, it is difficult to reconstruct the thermal history of carbonate strata in marine basins due to the lack of effective palaeo-thermometer. The carbonate cluster isotope is an index that can indicate the formation temperature of carbonate rock. It records temperature information in chemical bond through conjugated 13C-18O, and temperature information is revealed through changes in the abundance of conjugated 13C-18O, namely, the abundance of carbonate clumped isotope (Δ47) is closely related to the evolution of strata temperature. This paper reviews the application of carbonate clumped isotope palaeo-thermometer and discusses the existing problems and future development direction based on the basic principle and methods of carbonate clumped isotope thermometry and thermal history reconstruction, and combined with the case studies of thermal history reconstruction in marine basins in recent years. As a new palaeo-thermometer, carbonate clumped isotope shows great potential in the thermal history reconstruction of carbonate strata. Previous studies show that the maximum paleotemperature of the Bird Spring Formation in Arrow Canyon, Nevada, USA is about 175 ℃, and the maximum burial temperature of Permian Maokou Formation in the Sichuan Basin is 213-225 ℃. There is an abnormal high temperature of above 160 ℃ in the Ordovician strata of the Tarim Basin due to the Permian magmatic activity. We believe that the carbonate clumped isotope is still insufficient in the reconstruction of thermal history due to the immaturity of thermal evolution models, the recrystallization, and the change of burial temperature. Thus, we suggest that combining the carbonate clumped isotope, U-Pb dating, and other palaeo-thermometers to accurately reconstruct the thermal history of carbonate strata will be the future development direction.

As one of the major fractions of petroleum and/or source rock extracts, asphaltene is commonly characte-rized by complicate molecular structures as well as relatively higher molecular weight (MW). The asphaltene occluded biomarkers have been well introduced to be valuable for geochemical research whilst the actual molecular weight and molecular structures of asphaltene macromolecules studies show value in petroleum exploration and production, laboratory treatments as well as petroleum chemical storage and transportation etc. The structure, molecular weight and related experimental measurement methods of asphaltenes reported in this paper are reviewed, in an attempt to provide a more comprehensive understanding on the molecular structure, molecular weight and physicochemical properties of asphaltenes, so as to provide basic data for applying asphaltene geochemical research in the exploration and development study of conventional and unconventional reservoirs. In view of the different views on the structure and molecular weight of asphaltene molecules, the results are reviewed, the main reasons for the controversy are discussed based on the current status of experimental measurement technology, and the future development trend of related researches is pointed out. The current understanding of the structure of asphaltene macromolecules is mainly based on two completely different models, i.e., the island model and archipelago model. The former suggests that asphaltenes have a single aromatic nucleus and the molecular weight characterized is relatively lower. The latter believes that asphaltenes have multiple aromatic nuclei and the molecular weight characterized is relatively higher. The above two models of asphaltene molecular structure are supported by their own experimental measurement results, among which the evidences of the "island" model mainly come from fluorescence spectroscopy, laser vaporization/laser ionization mass spectrometry (L2MS) analysis and stem from various ionization high-resolution (Fourier transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) analysis technologies. The evidences for the archipelago model mainly come from gas phase permeation measurement, size exclusion chromatography and chemical degradation.

The geological conditions of Hashan area on the northwestern margin of the Junggar Basin are complicated and it is difficult to explore. It is of great significance to clarify the sedimentary and evolutionary characte-ristics of source rocks in the Permian Fengcheng Formation in this area for expanding oil and gas exploration on the basin margin. Based on the analysis of whole-rock XRD, elemental geochemistry, organic matter abundance, thin section identification, and lithofacies association characteristics, this paper conducted a comparative analysis of the sedimentary characteristics, lithology, and lithofacies association characteristics of the Fengcheng Formation in the Mahu Sag and Hashan area, restored the ancient sedimentary environment evolution sequence in the study area, and established a model of ancient sedimentary evolution. The research results show that the lithofacies association characteristics and ancient sedimentary environment evolution sequence of the Fengcheng Formation in the Hashan area are highly similar to those in the Mahu Sag, which are generally fine-grained sediments mixed from multiple sources in an alkaline lake with a volcanic background, and various lithofacies associations are developed. The sedimentary paleoenvironment has phased evolution characteristics. The large number of typical alkaline minerals in the second member of Fengcheng Formation in Hashan area reveals the development of another lake basin center in addition to the Mahu Sag. During the deposition of the first member of Fengcheng Formation (P1f1), the lake level was relatively higher, the water salinity was low, the climate was semi-arid, and volcanic sedimentation was developed, with lithofacies mainly composed of organic-rich blocky tuffaceous limestone. In the lower part of the second member of Fengcheng Formation (P1f2), the basin began to shrink, the climate became relatively drier, the water became saltier, the environment became more limited, and the lithofacies were mainly organic-rich layered dolomitic mudstone. In the top of the P1f2 and the lower part of the third member of Fengcheng Formation (P1f3), the environment was relatively closed, the water salinity was higher, a large number of alkaline minerals were developed, and the lithofacies were mainly organic-rich layered alkaline dolomitic mudstone and organic-rich layered mixed shale. In the upper part of P1f3, the input of terrigenous debris increased, salinization weakened, a fan-delta system was developed, and the lithofacies were mainly organic-rich blocky fine sandstone. The sedimentary environment of the Fengcheng Formation has a controlling effect on organic matter enrichment. Overall, a deep-water environment with less input of debris, warm and humid conditions, and relatively lower salinity is more conducive to organic matter enrichment.

The lower play (Permian to Triassic) in the hinterland is the most important strategic succession field for oil and gas exploration in the Junggar Basin. Multiple wells have been drilled into high-quality clastic rock reservoirs below 6 000 m, greatly breaking through the deadline of buried depth of traditional clastic rock effective reservoirs. It has been made clear that the development status and pore evolution process are the key issues that determine whether oil and gas can be accumulated. Taking typical drilling wells in the hinterland as an example, this paper comprehensively analyzed the petrology, physical properties and pore structure characteristics of deep and ultra-deep clastic reservoirs in the hinterland of the Junggar Basin from a qualitative and quantitative perspective, and quantitatively restored the pore evolution process by integrating the microscopic analysis of rock thin sections, porosity and permeability tests, image analysis technology, quantitative characterization of porosity evolution, temperature measurement of inclusions, basin modeling and other methods. The results show that the clastic rock in the lower play of the hinterland is mainly developed in the Permian Upper Wuerhe Formation, Triassic Baikouquan Formation and Triassic Kelamayi Formation, of which the sand in the Triassic Baikouquan Formation is the most developed, followed by the Permian Upper Wuerhe Formation and Triassic Kalamayi Formation. There is little difference in rock types among different layers, which mainly composed of lithic sandstone with a small amount of feldspar lithic sandstone. The composition of rock debris is mainly medium-basic volcanic rock debris, with low content of feldspar and quartz, and the sum of them is generally less than 20%. The Kelamayi Formation is dominated by primary pores with the best reservoir property and the highest porosity of 13.18%. The Upper Wuerhe Formation and Baikouquan Formation are dominated by secondary corrosion pores, and the corrosion materials are mainly medium-basic volcanic debris, laumontite cement and a small amount of feldspar. The reservoir properties of them are not as good as those of the Kelamayi Formation. The pore evolution of the Kelamayi Formation has experienced weak compaction (21.08% pore reduction by compaction), weak cementation (2.88% pore reduction by cementation), and weak corrosion (1.4% pore increase by corrosion). Today's high porosity is mainly due to the large amount of preservation of primary pores under weak compaction and late weak cementation. The Baikouquan Formation and Upper Wuerhe Formation have undergone strong compaction (26.60% and 26.43% pore reduction by compaction, respectively), strong cementation (7.43% and 11% pore reduction by cementation, respectively), and strong corrosion (6.32% and 4.21% pore increase by corrosion, respectively). Secondary corrosion is the main way for them to increase porosity, but it is insufficient to compensate for the porosity reduction effect of strong compaction and cementation, resulting in lower porosity in the two formations.

From the Late Carboniferous to the end of Middle Permian, the most intense glacial event in history of Phanerozoic occurred and it is also the last transition period from icehouse stage to greenhouse stage in geological history. In this paper, the paleotemperature and paleoclimate in the first member of the Middle Permian Maokou Formation (Mao-1) were restored by means of thin section identification, scanning electron microscope, major elements, trace elements, carbon isotopes, oxygen isotopes and strontium isotopes, and the major climate evolution process and its driving mechanism in the Middle Permian were discussed. The results show that the biological assemblage type (mainly composed of foraminifera, brachiopods and molluscs, without reef-building organisms or calcareous green algae) and rock structure characteristics (supported by bioclastic and plaster, without oolitic or other non-skeletal particles) of the limestone-marl alternations in the Mao-1 member are similar to those of the international typical cool-water carbonate. During the limestone sedimentary period, the paleotemperature of seawater was 3.72 to 12.38 ℃ (8.15 ℃ in average, δ18O standard) or 13.79 to 14.28 ℃ (13.90 ℃ in average, ω(Mg)/ ω(Ca) standard), while during the marl sedimentary period, the paleotemperature of seawater was 7.00 to 14.24 ℃ (10.97 ℃ in average, δ18O standard) and 13.82 to 15.41 ℃ (14.27 ℃ in average, ω(Mg)/ω(Ca) standard). The paleotemperature changes in the sedimentary period of Mao-1 Member was mainly driven by the short eccentricity cycle of Milankovitch. The cyclical change of the short eccentricity was the driving mechanism of paleotemperature and paleoclimate cycle changes.

Due to the high cost for exploration and development of tight oil reservoirs, it is an urgent problem to achieve profitable development of tight oil. According to the characteristics of tight oil reservoir in the eighth member of Triassic Yanchang Formation (Chang 8) in Honghe oil field, Ordos Basin, this paper highlighted single well information, started with the key parameters affecting the economic benefit of tight reservoir-single well economically recoverable reserves, and established a series of determination methods and process of geological evaluation parameters for profitable development of tight oil reservoirs based on single well economically recoverable reserves. Considering the particularity that the single well recoverable reserves of Chang 8 tight oil reservoir in Honghe oil field was controlled by fractures, the fracture development degree was added in the study of determination of the geological evaluation parameters. Five parameters, including single well technically recoverable reserves, net pay thickness, effective porosity, oil saturation and fracture development degree, were selected for classification and subdivided into six types. By compiling the intersection diagram of single well technically recoverable reserves and net pay thickness, the cutoffs of geological parameters were determined comprehensively by comparing the economic cutoffs and the classification of reservoir geological parameters under two scenarios. The method was applied to Chang 8 reservoir in Honghe oil field, and its feasibility was verified. The practical application shows that this method can provide effective technical support for sweet spot screening and development and deployment optimization in tight reservoirs.

The Middle Permian Maokou Formation in the Sichuan Basin is an important natural gas payzone. Recently, Zhejiang Oilfield Company of CNPC obtained industrial gas flow of vertical well test 42×103 m3/d and horizontal well (well DB 1H) test 556×103 m3/d in the limy source rock gas reservoir of eyelid and eyeball- shaped limestone in the first member of the Maokou Formation in well DB 1, Da'an exploration area, western Chongqing. A breakthrough has been made in the unconventional gas exploration of argillaceous limestone in the southern Sichuan and western Chongqing area, showing good exploration prospects in this area. The eyelid and eyeball-shaped limestone in the first member of the Maokou Formation in the Sichuan Basin has the characteristics of self-generation and self-storage, continuous and stable distribution and high thermal maturity. The limestone of central gentle slope facies shows no water sensitivity or acid sensitivity, and is dominated by carbonate brittle minerals, which is ideal for acid-fracturing development. It is of great significance to study the characteristics and main controlling factors of the organic rich limestone reservoir. Taking well DB 1 as an example, this paper carried out a study on the petrology, sedimentology and reservoir characteristics of the first member of the Maokou Formation, and it is found that, deposited on the central gentle slope with frequent water activity and abundant organism, the dark gray to black micrite with high organic matter content has good physical properties. In general, submember c has better physical properties than submember a. The development degree of macropores in eyelid-shaped limestone is higher than that in eyeball-shaped limestone, and the development degree of micropores is not much different. The main pore types of the first member of the Maokou Formation include dissolution pores, fractures, clay mineral apertures and organic pores. The pores in clay minerals (mainly talc) and organic matters are mainly distributed in the eyelid-shaped limestone. Depositional process and diagenesis are the main factors controlling the development of the eyelid and eyeball-shaped limestone reservoirs. The central gentle slope facies controls the development and distribution features of the organic-rich micrites. Diagenesis as well as fracture and dissolution effects improve the reservoir capacity of limestone, which is critical for hydrocarbon accumulation. Stable and high yield commercial gas flow was obtained in the vertical wells and horizontal wells in the first member of the Maokou Formation which has high organic matter content in well DB 1 block in the western Chongqing area, indicating that the accumulation and occurrence conditions of limestone source rock gas are good in the first member of the Maokou Formation. It has two kinds of accumulation modes with self-generation and self-storage dominance and short distance aggregation of local structural bands, and has the characteristics of continuous distribution of gas reservoir and large resource scale. The "continuous gas reservoir: in the limestone source rock in the first member of the Maokou Formation has great exploration potential, which will become an important exploration target with good potential in the Sichuan Basin.

The conclusion of "near-source accumulation" of tight oil is inferred based on the reservoir characte-ristics that crude oil is difficult to migrate laterally for a long distance in low-permeability reservoirs, yet there has been no direct geochemical evidence for a long time. Based on the analysis of the characteristics of source rocks and the source differences of oil in the near-source assemblage (Chang 6 member to Chang 81 sub-member) of the Tirassic Yanchang Formation in the Ordos Basin, this paper explores the geochemical basis of tight oil near-source accumulation and explains its cause. The results show that the crude oil in the near-source assemblage comes from the in-situ Chang 7 source rocks, and even the oil sources in the adjacent blocks are different. It is difficult for crude oil to undergo large-scale lateral migration in a tight reservoir. The biomarker compounds of Chang 7 source rocks in the Ordos Basin have significant differences in the plane and are distributed in a circularbelt along the sedimentary center. The oil source difference caused by the combination difference ofbiomarker compounds in different facies zones is the fundamental reason for the predecessors' discovery of "near-source accumulation" of tight oil. The "near-source accumulation" of tight oil has changed the previous view that oilsource correlation is a generalization of the whole basin and the source rocks of the same layer, and has important significance for the zoning and fine evaluation of different types of oil and gas resources in a single basin in the future.

Pore structure, as the focus of shale reservoir research, has important influence on the occurrence of shale oil. In this paper, 10 shale core samples from the 7th member of Triassic Yanchang Formation (Chang 7 member) in Huachi area, Ordos Basin were selected to carry out scanning electron microscope (SEM) observation and low-temperature nitrogen adsorption experiment, and the fractal dimension was calculated to quantitatively characterize the pore structure of shale in the research area combined with fractal FHH model. On this basis, the relationship between fractal dimension and pore structure parameters and oil-bearing parameters was discussed, and the main influencing factors of pore development of shale in the Chang 7 member were determined. The results show that the shale of the Chang 7 member in Huachi area has high organic matter abundance, which are good-to-excellent source rocks mainly composed of quartz and clay minerals, with good oil-bearing property (up to the middle oil-bearing level) and mobility. The reservoir space is dominated by intergranular pores, intragranular pores and a small amount of organic pores. There are two types of pore morphology, namely, parallel plate-shaped slit+unilateral slit and ink bottle-shaped + parallel plate-shaped slit. The pores are mainly micropores and mesopores, with macropores less developed. Most samples have fractal characteristics. The fractal dimension D1 of small pores is between 2.264 7 and 2.714 9, and the fractal dimension D2 of large pores is between 2.373 3 and 2.77 7. Among them, D2 has a good correlation with surface area, pore volume, average pore diameter and S1, which can characterize the development characteristics of pore structure and oil-bearing property of shale, while D1 can only characterize the mobility of shale oil. The pore development of shale is mainly controlled by TOC and quartz content, and has a certain relationship with feldspar content, while clay mineral content is not the main influencing factor.

The result of mining right bidding, affected by many factors, has strong uncertainty. Especially in areas with low exploration degree, how to accurately carry out block economic evaluation is a key issue in current research. Based on the expected monetary value (EMV) method, this paper considers the "risk-value" two-factor model to quantify the geological risk, uses the probability distribution model to quantify the uncertainty of resources, defines the basis for the selection of key parameters, sorts out the economic evaluation scheme for shale gas blocks in areas with low exploration degree, and carries out the application to a shale gas block in the Guizhong Depression in Dianqiangui Basin, southern China. The results show that the method comprehensively considers multiple scenarios under different combinations of schemes, such as resource potential, engineering and technical conditions, development scheme, expected economic value, and oil and gas subsidy policies. The multiple sets of economic evaluation schemes formed can provide diversified block economic evaluation parameter data for decision makers, and can effectively guide the decision-making of block bidding scheme.

In this paper, the mineralogical composition, sedimentary structure, laminar type, pore size distribution, pore volume, specific surface area, number of laminae and morphological characteristics of dissolution pores of the lacustrine shale from the upper sub-member of the fourth member of the Paleogene Shahejie Formation of the wells NY1 and FYP1 in the Dongying Sag of Bohai Bay Basin were finely characterized by a combination of core observation, thin section observation, nitrogen adsorption and X-ray diffraction. On this basis, the main lithofacies types and laminar characteristics, the pore size, pore volume and specific surface area of different lithofacies, and the pore and laminar characteristics of carbonate-rich shale in this area were summarized. The results show that there are four lithofacies types in the Dongying Sag: organic-rich laminated argillaceous limestone, organic-rich laminated sandy limestone, organic-bearing laminated sandy limestone and organic-bearing massive limestone. The microscopic features of the laminae are mainly flat, lenticular, interbedded and undulating. The measured nitrogen adsorption data show that the carbonate-rich shale in the Dongying Sag has a larger pore volume and specific surface area. At the same time, the development of dissolution pores and laminae allows the carbonate-rich shale to have higher storage capacity and horizontal permeability. Therefore, the carbonate-rich shale is a high quality reservoir in the Dongying Sag.

The Sverdrup Basin is one of the important petroliferous basins in the Arctic. It has abundant oil and gas resources, but the exploration degree is relatively low. Based on the IHS database and literatures in the public domain, this paper documented the geological characteristics and distribution of oil and gas in the Sverdrup Basin, and classified the petroleum systems and hydrocarbon plays in the basin. The undiscovered hydrocarbons were eventually assessed by Monte Carlo simulation and the favorable exploration areas were predicted. The investigation results show that the discovered oil and gas accumulations are mainly distributed in the western area of the basin, which consists of Sabin and Edinburgh sub-basins. Oil and gas are mainly reserved in the Jurassic and Triassic clastic reservoirs. Two petroleum systems, which are the Paleozoic and Mesozoic systems, were identified in the basin. The Mesozoic petroleum system has a far greater exploration potential. Undiscovered recoverable reserves (mean value) in the Mesozoic petroleum system are 474.81 MMbbl (1 MMbbl=1×106 bbl, 1 bbl=0.137 t) of oil, 13 620.82 Bcf (1 Bcf=1×109 ft3, 1 ft3=0.028 3 m3) of natural gas and 63.66 MMbbl of condensate, amounting to 2 808.61 MMboe (3.85×108 t), of which the natural gas accounts for 80.82%. The Lower Jurassic structural hydrocarbon play in the western area of the basin, the Upper Triassic-Lower Jurassic structural hydrocarbon play in the Edinburgh sub-basin and the Upper Jurassic structural hydrocarbon play in the Sabine sub-basin are the most promising exploration areas.

In order to reveal the differential deformation characteristics of the Wangfu Fault Depression in Songliao Basin and study the regularity of the deformation mechanism of boundary normal faults, this paper, based on the structural analysis and fault differential analysis, discusses the controlling factors and genetic mechanism of differential deformation of boundary normal faults in combination with the advantages of tectonophysical simulation in "continuous forward modeling" and "control variables". The results show that: (1) According to the intensity of fault activity, four regional tectonic evolution stages can be divided. The boundary normal faults in the west of Wangfu Fault Depression is the most active, but the dip angle of the faults gradually increases from north to south, showing a "convex" shape locally. (2) Combining tectonophysical simulation with actual geological background, it is showed that the shape of boundary normal fault was controlled by three main factors, including lateral lithologic change, syntectonic sedimentation and pre-existing uplift of basement. If boundary normal faults are developed in strata with different lithology at the same time, or accompanied by strong syntectonic sedimentation, the dip angle will change. In addition, the extension of the fault near the hard basement bulge will change its trend and continue to spread around the bulge top, resulting in the local appearance of "uplift".

In order to understand the connotation and substantive relationship among oil and gas resources, reserves and production on a deeper level, this paper made an in-depth analysis and elaboration on the relationship among the three from the perspectives of theoretical logic and practical transformation, and presented suggestions for the development direction of resource assessment based on the analysis of application status. Resources, reserves and production are estimated quantities of oil and gas mineral resources under different levels of understanding. In China's classification system, reserves and resources are in a parallel relationship, and reserves and production are in an inclusive relationship. Both resources and reserves are geological meanings. The transformation from resources to reserves is affected by factors such as national spatial planning, mining right setting, theoretical technical and economic conditions, and the transformation from reserves to production is affected by factors such as reserves upgrading and transformation, whether to convert to mining, recovery factor, etc. China still has some deficiencies in resource assessment and release, as well as quantitative prediction of resources, reserves and production, which is also an important reason for the cognitive confusion of "China has rich resource potential but it is difficult to increase reserves and production". The enrichment and development of resource assessment contents and results application analysis will help to form a comprehensive and in-depth understanding of the current situation of oil and gas resources. It should be further explored and developed in the future from the following respects: mobility classification of assessment results, assessment of (undiscovered) recoverable resources and application analysis of results.

The reform and new policies of national oil and gas mining rights system have led to the increasing number of mining rights blank areas. In order to tap and enhance the strategic value of oil and gas in blank areas, promote the discovery and full use of oil and gas resources, and ensure the national energy security, this paper, by analyzing the structure and distribution characteristics of China's oil and gas resources, focusing on the main mining rights blank areas on land, and studying on oil and gas geological conditions and key reservoir-forming factors, carries out the optimization of strategic area selection and key exploration fields according to the process of stepwise classification. It is pointed out that the natural gas in the deep depression of the north and south platform basins of the Tarim Basin, the Carboniferous natural gas and the Jurassic coalbed gas in the northeast of the Junggar Basin, the Neopaleozoic tight gas and coalbed gas in the eastern and northern margins of the Ordos Basin, and the marine shale gas in the extrabasinal gentle structural area of the Middle and Upper Yangtze are the key directions for future strategic area selection. Combined with the characteristics and key problems of oil and gas geology in various fields, suggestions are put forward for deepening research, technical research direction and evaluation of selected areas.

The exploration and development of shallow shale gas has the advantages of low cost and fast production reduction, so it has attracted wide attention. The shale gas in the Lower Silurian Longmaxi Formation (S1l) in Taiyang block of Zhaotong National Shale Gas Demonstration Zone has the characteristics of shallow burial depth and high gas content, showing good exploration potential. However, the gas-bearing distribution and major controlling factors of shallow shale gas in this research area are rarely studied previously. In order to enrich the research in this field, this paper analyzes the gas-bearing characteristics and the major controlling factors of the shale samples of Long-1 subsection (S1l1) in the Taiyang block. The results show that the total gas content of S1l11-1 is the highest in the study area, the gas content gradually decreases from bottom to top, and areas with high shale gas content in S1l1 appear in the north and south of the study area on the plane. Organic matter content, mineral components, reservoir properties and external preservation conditions have a certain role in controlling the gas properties of shallow shale in S1l11 subsection of the study area. Organic matter is the primitivesubstance that generates shale gas, at the same time, the organic matter hole formed by hydrocarbon cracking sprovides a lot of storage pace for shale gas, while the content of organic matter is the major controlling factor of the total gas content. The high content of silicoide is conducive to later fracturing development. The adjacent rock strata of S1l11 subsection in the study area are compact in lithology, with good sealing property, showing the characteristics of slight overpressure and overpressure, which effectively prevents the escape of shale gas, and has broad exploration prospects.

In recent years, drilling in Xinhe area on the southern slope of Kuqa Depression, Tarim Basin revealed that the Cretaceous Yageliemu Formation has active hydrocarbon display and high exploration potential in the field of stratigraphic-lithologic traps, which is an important direction for the next strategic breakthrough. Based on the core, well logs, drill cuttings and 3D seismic data, this paper integrated the analytical methods of core facies, electrofacies, wavelet transform, "impression method" paleogeomorphic restoring, seismic facies, seismic attributes, and coherence cube slicing to study the depositional system of the Cretaceous Yageliemu Formation in Xinhe area under the sequence stratigraphic and paleogeomorphic controls. The study shows that there are two types of paleogeomorphology developed in Xinhe area: (ⅰ) western multi-stage slope breaks, and (ⅱ) eastern thrust cliff paleogeomorphology. The Cretaceous Yageliemu Formation can be classified as a third-order sequence SQ1, which includes the lowstand systems tract (LST), transgressive systems tract (TST) and highstand systems tract (HST), corresponding to the three-phase seismic reflections of this formation overlying the western slope, respectively. The LST slope fans and HST fan deltas of the Yageliemu Formation were deposited above the western multi-stage slope breaks, and TST-HST subaqueous nearshore fans were deposited below the eastern thrust cliff, with erosional valleys on the cliff serving as the feeder channels and providing sources for the subaqueous fans. In situ mature hydrocarbon source rocks of the Triassic Karamay Formation are developed in Xinhe area, which is the migration direction of oil and gas far away from hydrocarbon source, indicating excellent source rocks and reservoir forming conditions. The stratigraphic-lithologic traps of the LST slope fan and TST-HST subaqueous nearshore fan located in the northern part of the thrust cliff are lying on the Triassic source rocks and have great exploration potential, which can serve as the main targets for the next subtle oil and gas exploration in this area.

There are various types of crude oil in the Liaohe Depression, Bohai Bay Basin, among which heavy oil accounts for more than 50% of the oil and gas reserves and production. Therefore, it is of great significance for future exploration and development to study the main controlling factors of oil densification in the Liaohe Depression and to understand the distribution pattern of heavy oil. Based on the systematic understanding of heavy oil reservoir exploration and development in Liaohe oilfield for decades of years, and by aiming at the geological characteristics of heavy oil reservoirs such as "edge, shallow, unconsolidated, early, falling, loss, capping", this paper discusses the distribution and densification reasons of heavy oil from six aspects, including structural pattern, reservoir characteristics, reservoir burial depth, underground fluid, capping conditions, oxidation and biodegradation. The densification mechanism and controlling factors of heavy oil reservoirs in the Liaohe Depression are basically clarified. Through the study of heavy oil densification factors, it is found that structural pattern is the main factor controlling heavy oil distribution, geological conditions such as reservoir, burial depth, underground fluid and cap rocks are important factors controlling heavy oil densification, while biodegradation and oxidation are the keys for heavy oil densification. Oil and gas reservoirs accumulate around sags in the Liaohe Depression. There are three rings around the oil-generating sags from the inside to the outside. The inner zone is dominated by natural gas and condensate gas, and the buried depth is generally more than 3 500 m. The middle zone is dominated by light oil, partially enriched with natural gas and heavy oil, with a buried depth of 1 700-3 500 m. The outer zone is dominated by heavy oil, and the buried depth is generally less than 1 700 m.

Under the influence of the Emei Taphrogenesis, a set of volcanic clastic rocks were developed in the Wujiapingian age of Permian in the northern Sichuan Basin. The lithology is highly heterogeneous, and the pore structure of reservoir is complex. In order to further clarify the characteristics and formation mechanism of volcanic clastic rock reservoirs in the Wujiaping Formation and confirm the exploration potential, this paper analyzes the reservoir characteristics and formation mechanism of volcanic clastic rock reservoirs in the Wujiaping Formation in the northern Sichuan Basin based on outcrop and actual drilling data and combining with core section observation, geochemistry analysis, argon ion buffing scanning electron microscope, combined determination of cap micro pores and other methods. It is concluded that the volcanic clastic rocks can be divided into three rock types: tuffaceous mudstone, argillaceous tuff and sedimentary tuff. The reservoir space is dominated by nano-scale clay mineral shrinkage pore and organic matter pore and micron-scale organic acid dissolution pore and micro fracture. The reservoir physical property is characterized by medium to high porosity and ultra-low permeability, and the tuffaceous mudstone has the best physical property among the three rock types. The analysis of the controlling factors of the reservoir shows that the near-crater slope and shelf environment is favorable for the development of volcanic clastic rock reservoirs, and the devitrification of volcanic ash and secondary organic acid dissolution are the main causes for the formation of pores in the reservoir.

The reservoir space of tight reservoir with low-permeability is controlled by micro and nano scale pores, making the influence of capillary force significantly enhanced. Therefore, understanding the microscopic charging characteristics of oil and gas is the basis for analyzing the migration and accumulation of reservoirs. In this paper, the self-developed on-line three-dimensional microscopic imaging system for core fluid displacement is used to observe the oil charging process of two tight reservoir samples, and core-level and pore-level quantitative analysis methods for oil content characteristics are proposed. Taking the on-line nuclear magnetic resonance testing with the same process of displacement as a contrast, it is revealed that the average difference of on-line 2D DR (Digital Radiography) images at different times can be used to evaluate the overall oil content change of the sample. The calculation method of pore level fluid saturation based on high-precision pore network extraction algorithm realizes the quantitative evaluation of oil charging degree of the CT resolved pores and pore throats. The combination of multi-level data and different methods can meet the different needs of different researches on dynamic feature capture, pore resolution and imaging field of vision. The analysis results show that the oil saturation of two rock samples from different tight reservoirs in the Ordos Basin increases rapidly at the beginning and slows down later with oil injection increasing. At the same injection flow rate, the oil saturation of the sample with higher permeability increases faster at the initial oil charging stage, making its final oil saturation higher. With the increase of oil injection, the oil saturation of macropores in the sample with higher permeability continuously increases, while that of macropores in the sample with lower permeability shows a U-shaped change, showing the characte-ristics of repeated occupation of pores by oil and water.

The lack of helium resources accounts for the limited helium supply in China. It is of great significance to classify of helium-enriched natural gas according to the characteristics of helium reservoirs and the main controlling factors of helium enrichment, thus the exploration and development of helium can be promoted and the safety of helium use in China may be ensured. Based on the origin of helium, this paper classifies the helium reservoirs by the consideration of the abundance of helium resources, the spatial horizon of uranium and thorium radioactive elements, the types of carrier gas reservoirs, and the main controlling factors of helium accumulation. The helium gas resources can be characterized into two types: crust-mantle mixed type and crust-source type. Crust-source type can be further classified into crust-source far-source type (including hydrocarbon associated type and water-soluble gas type) and crust-source near-source type (shale gas type) with different characteristics. In terms of helium reservoirs discovered in China, only crust-source helium which was formed together with hydrocarbon gas reservoirs has industrial utilization value due to the great resource potential, although its resource grade is relatively low. The main controlling factors of helium accumulation in the crust-source far-source type and crust-source near-source type are roughly the same, but there are differences in helium sources and migration pathways.

A large number of high-sulfur-content carbonate gas reservoirs have been discovered in the northeastern part of the Sichuan Basin, and their reserve accounts for more than half of the total natural gas reserves in the basin. However, sulfur deposition has been a major problem for a long period which is restricting for the efficient development of high-sulfur-content gas reservoirs. In this paper, sulfur deposition experiments in carbonate rock samples were carried out with high-sulfur-content natural gas by the means of micro-CT scanning, scanning electron microscopy, gas chromatograph and energy spectrum analysis. The changes of the microscopic pore structure of the samples and gas composition before and after the experiments were quantitatively obtained, and the 3D visualization of sulfur deposition in reservoir rocks was achieved for the first time. Results show that after sulfur deposition experiment, the total sulfur content in high-sulfur-content gas decreased by 12.58%, and the organic sulfur component decreased by 9.07%. Sulfur particles were mainly deposited in rock pores with a radius of less than 500 μm, resulting in decreases in rock permeability and porosity by 34.40%-67.80% and 3.77%-7.69%, respectively. This study further improved the understanding of the microscopic characteristics of sulfur deposition and provided support for the formulation of production enhancement measures for high-sulfur-content gas reservoirs.

The Late Neoproterozoic to Early Cambrian is a remarkable time-interval that witnessed significant biolo-gical and environmental evolutions, during which, the deep ocean was extensively anoxic, whereas the surface ocean was characterized by considerable fluctuations in redox conditions. The Lower Cambrian Yanjiahe and Shuijingtuo formations in the Luojiacun section from the Three Gorges area situated in Yichang city of central China were studied in this paper. According to biostratigraphic and carbonate carbon isotope stratigraphic correlation, the Yanjiahe Formation and Shuijingtuo Formation were assigned to the Cambrian Terreneuvian Stage 1-2 and Series 2 Stage 3, respectively. In view of this time-frame, the response of inorganic and organic carbon isotopes decoupling to water redox environment transition was systematically studied. The rise of anoxic bottom water during transgression provided sufficient nutrients and essential trace elements for primary productivity in the surface ocean. The increase of net productivity led to oxygen consumption increase and the changes of redox environment in the water column. Photosynthetic oxygen temporarily oxygenated the surface seawater, and dissolved oxygen was gradually consumed by the oxidation of DOC reservoirs, resulting in gradual expansion of oceanic anoxia, which was conducive for the preservation of organic matters. The oxidation of DOC in the surface water accounted for the formation of authigenic carbonates that were 13C-depleted, while the large oceanic DOC reservoir in the Early Cambrian buffered the change in δ13Corg, which eventually manifested as decoupled carbon isotope during the transition time of Cambrian Stage 2-3.

The lacustrine dark shale deposits of the Upper Cretaceous Qingshankou Formation in the Central Depression of Songliao Basin contain a considerable amount of shale oil resources, among which the shale oil exploration of the Qingshankou Formation in the Qijia-Gulong Sag has made a major breakthrough. In this paper, methods of sealed thermal release, combined with organic solvent extract and Rock-Eval, has been used for the comprehensive evaluation of shale oil-bearing capacity of the Qingshankou Formation. The TOC of shales from the Qingshankou Formation in the study area range from 1.48% to 6.97% with an average value of 3.40%. The values of Tmax range from 440 ℃ to 453 ℃ with an average of 448 ℃ for the samples after extraction, and the production index ranges from 0.28 to 0.67, indicating a middle stage of oil generation window. The shale oil contents of the studied samples range from 4.00 mg/g to 19.49 mg/g with an average value of 13.74 mg/g. The contents of free oil range from 3.41 mg/g to 13.63 mg/g with an average value of 8.70 mg/g; while the content of adsorbed oil ranges from 0.60 mg/g to 9.43 mg/g with an average value of 5.04 mg/g. Free oil is made up of restricted oil and movable oil in the proportion of 1∶1. The content of restricted oil of the studied samples ranges from 1.81 mg/g to 8.49 mg/g with an average of 4.15 mg/g; while the content of movable oil ranges from 1.36 mg/g to 11.05 mg/g with an average of 4.55 mg/g. The movable oil resource is 12 kg/m3 based on the average content of mobile oil, which reveals good resource potential of movable shale oil in the first member of Qing-shankou Formation of the Sanzhao Sag.

Tight oil and gas is an important part of China's oil and gas resources, and the study of related pore-throat structure is conducive to the enrichment and improvement of tight oil and gas geological theory. Taking the tight reservoir of the Triassic Yanchang Formation in the Ordos Basin as an example, combined with large-field image stitching method and image pore extraction method, this paper established a new method for pore-throat structure characterization of tight reservoir with high-temperature and high-pressure alloy injection. Results show that the alloy injected into the pores of tight reservoirs can reflect the characteristics of pore connectivity better, and the pore morphology and structure are easier to be identified. The large-field image stitching method solves the problem of strong heterogeneity of pore distribution and poor representativeness of small-field observation. The tight reservoirs of the Yanchang Formation in the Ordos Basin are mainly composed of intergranular pores, intragranular pores, and intergranular-intragranular mixed pores, among which the intergranular pores are mostly developed. There are five types of throats, including pore shrinkage throat, neck constricted throat, bundle throat, sheet throat and curved sheet throat, among which the curved sheet throat is mostly developed. The porosity of quartz and feldspar is significantly larger than that of other minerals, contributing 74% to the surface porosity of tight reservoir, and is an important occurring space for tight oil and gas.

Exploration discoveries have been made in the Middle Permian of the Sichuan Basin, indicating great exploration potential. However, the Middle Permian has obvious tectonic-sedimentary variation, resulting in complexity of hydrocarbon accumulation mechanism. The reconstruction of sequence lithofacies paleogeography is of great significance to understand the tectonic-sedimentary evolution, sedimentary formation and hydrocarbon exploration. In this paper, the lithofacies palaeogeography during the Middle Permian Qixia-Maokou period in the Sichuan Basin was reconstructed with the third order sequence as the minimum longitudinal mapping unit based on oil and gas exploration results as well as typical drilling and outcropping data. Five third-order sequences for the Middle Permian in the Sichuan Basin were supposed in this study including: SQq1 (from the Liangshan Formation to the section B of the first member of the Qixia Formation), SQq2 (from the section A of the first member to the second member of the Qixia Formation), SQm1 (from the first member to the section C of the second member of the Maokou Formation), SQm2 (from the section B to the section A of the second member of the Maokou Formation), and SQm3 (from the third to the fourth member of Maokou Formation). During the deposition of SQq1 and SQm1, transgression and filling were dominant, and spot and banded beach bodies in some palaeo-highlands of the basin were discovered. During the deposition of SQq2, SQm2 and SQm3, continuous regression and geomorphic differentiation were dominant, the carbonate platforms depositional system with edge were developed in the margin parts of the basin, and large scale multi-stage and multi-zone beach bodies could be formed in the platform. SQq2 was the main shoal-forming stage in the Middle Permian. The relatively long regressive process [JP+1]and local block uplift promoted the formation of large scale multi-stage and multi-zone shoals in the platform margin of the western Sichuan Basin and the southern part of the central Sichuan Basin. During SQm3 period, the sedimentary differentiation in the northern Sichuan Basin was obviously intensified, and it was transformed into an alternate uplift and sag pattern with platform margin, slope and shelf. The platform margin and intra-platform shoal of the HST during the deposition of SQq2 and SQm3 provided material basis for dolomitization, dissolution and other later constructive diagenetic transformation. Therefore, the delineation of slope break zone geomorphology and the prediction of platform margin and intra-platform shoal should be regarded as the focus of further exploration.

The Upper Triassic Xujiahe Formation in the Xinchang structural belt of the Western Sichuan Depression is an important exploration target for tight sandstone hydrocarbon in the Sichuan Basin. Several studies are carried out in this paper to improve the effectiveness of exploration and development including the characteristics of oil and gas movement with a view of dynamic point combining with fluid dynamics, determine the distribution characteristics of oil and gas in combination with static research results, and study the relationship between hydrocarbon enrichment and formation pressure. Overpressure is developed in the study area, and the degree of overpressure in the third member of Xujiahe Formation is the highest. Whilst the formation pressure of the main gas producing layer, the second member of Xujiahe Formation, is generally between 60-80 MPa with the maximum residual pressure reaches 40 MPa. The residual pressure gradients in most areas distribute between 0-3 MPa/km and up to 10 MPa/km as the highest. According to dynamic hydrocarbon enrichment theory and the relevant research on residual pressure and residual pressure gradient, it is considered that it has an important relationship with faults, fluids, hydrocarbon distribution and production performance. The area with higher residual pressure gradient (1-2 MPa/km) both improves fluid migration capacity and provides favorable reservoir, which is conducive to long-term high-yield and stable production.

In order to establish the relationship between hydrocarbon characteristic variations and dynamic environments, the differences of hydrocarbon geochemical characteristics of reservoirs in various pressure systems (overpressure zone, transitional pressure zone and normal pressure zone) were studied. The Dongying and Zhanhua sags in the Jiyang Depression of the Bohai Bay Basin were taken as examples in this paper, the variations of sterane isomerization parameter, sterane light/heavy ratio with depth were revealed. The transition from overpressure charging to normal pressure driving was clarified. The typical profiles of the Boxing (single pressure structure) and Bonan (composite pressure structure) sub-sags in the Dongying and Zhanhua sags, respectively, were selected for the differential analyses of geochemical parameters and corresponding dynamic conditions in various belts. The variations of the geochemical parameters showed high correlations to overpressure driving and buoyancy driving. The development ranges of abnormal pressure during reservoir formation were studied as well, which are much larger than the present abnormal pressure distribution ranges. Especially in the step-fault zone belt, historic overpressure had greatly extended outwards. According to the geochemical characterization of dynamic conditions, the reservoir formation systems and hydrocarbon supply ranges were described in detail.

In order to clarify the source rock conditions and oil/gas potential of the Aixi Sag in the Yingen-Ejinaqi Basin, based on the analytical results of mudstone samples from two exploratory wells, a systematic evaluation of the source rocks was carried out in this paper, and the effective source rocks were supposed. The potential source rocks in the study area are mudstones developed in Cretaceous Wulansuhai Formation (K2w), Yingen Formation (K1y), Suhongtu Formation (K1s), and the third (K1b3), second (K1b2) and first member (K1b1) of Bayingebi Formation, among which the K1b3, K1b2 and K1b1 mudstones have the highest abundance of organic matter with the kerogen types of Ⅱ-Ⅲ at mature stages of thermal evolution. Elemental geochemical and biomarker data show that the paleoclimate during the deposition of source rocks was warm and humid, the sedimentary water was mainly fresh water, and the contribution of terrestrial organic matter was dominant. The favorite sedimentary paleoenvironment conducive to organic matter enrichment is high salinity and strong reducibility, and high productivity is the main controlling factor for the enrichment of organic matter. The lowest limit of TOC content of effective source rocks is supposed to be 0.85%, and the effective source rocks are mainly developed in K1b3, K1b2 and K1b1. They are mainly distributed in considerable areas in the southern, central, northern and western subsags. The total oil and gas resources in the study area are estimated to be around 5 091.05×104 t. Combined with the evidence of active oil and gas display, it is concluded that the study area has good oil and gas exploration potential.

Risk and uncertainty are coherent attributes in hydrocarbon play exploration, and comprehensive exploration strategy requires a deliberate consideration of risk aversion and an faithful understanding of uncertainty. According to the characteristics of SINOPEC oversea oil and gas exploration projects, as well as the exploration project evaluation criteria of international oil companies, this paper describes the establishment of value-determined standards and hydrocarbon play risk workflow by quantitative assessment of hydrocarbon generation and charge capability, reservoir quality, preservation condition, and trap validity of a play. According to data density, coverage and geological understanding, in accordance with bucket theory, the probabilities of occurrence of four risk factors were determined, and the chance of geologic success (COGS) of a play was obtained by multiplying the probabilities of each risk factor. This workflow provided a method for transferring qualitative geological understanding and exploration data to quantitatively assess the risk probability of each factors and overall COGS. The COGS values determine the play risk, which is a comprehensive reflection of the exploration phase and geological characteristics of the study block. The play risk workflow facilitates high grading areas, allows a focus on the exploratory and appraisal aspects, and provides a scientific basis for exploration investment decision.