Based on analyzing the history of shale revolution in the United States and the differences in geological and engineering characteristics of shale oil between continental basins in China and marine basins in the United States, the paper proposes ten noteworthy issues on continental shale oil revolution in China, including the application and evolution of the nomenclatures of shale oil and tight oil in U.S., the development process of shale oil/tight oil in U.S., the proposal and connotation of shale revolution, and the experience in system and mechanism that can be learned from successful shale revolution in U.S., the work pattern of shale oil in U.S., the relationship between the profit model of shale oil and investment channels, the relationship between production declines of shale oil, the concrete time when a breakthrough is made in shale oil exploration in China, the principles and standards for classification of shale oil, and the continental shale oil revolution in China. Research suggests that the concepts of shale oil and tight oil in North America are identical to some extent. The core of "shale revolution" in U.S. is to improve drilling and completion efficiency, reduce well construction costs, and increase single well production; the development stages of its work pattern is divided according to the changes in both well type and horizontal section length of horizontal well, as well as the development of hydraulic fracturing. The number of drilled and completed wells is an important indicator reflecting shale oil exploration and development. The profit models and investment channels of shale oil extraction are closely related. American companies’ pursuit of recovering investment as soon as possible to obtain profits leads to the general adoption of a production model based on pressure release, with a rapid decline in yield and an L-shaped production curve. In terms of system and mechanism, we should draw on the experience from the application of market mechanisms, the project operation model of "oil companies+lean management", as well as the establishment of shared and open databases. From the perspective of resource base, engineering and technological capabilities, and production expectations, China has the basic conditions for the success in the continental shale oil revolution. All efforts should be made to promote the marketization, technological and management transformation of shale oil exploration and development, highlight the "qualitative development and quantitative breakthrough" of shale oil, and effectively transform resources into reserves and then into beneficial production, which can ensure the victory of shale oil revolution.

Green Earth is common homeland for human survival and development. Climate change has been a severe challenge to the earth's ecosystem since the global industrialization. Energy is the fundamental issue of human society. World energy transition is defined as the development trend of human energy utilization from firewood to coal, coal to oil and gas, oil and gas to new energy, and from carbon energy to carbon free energy and the process of fundamental transition for main energy factors including energy form, energy technology, energy mix and energy management.Energy system consisted with "New energy"+"Smart energy" and characterized with clean, carbon free, intelligent and efficient as the core is the development trend and direction of world energy transition. The world energy transition has "two driving forces and one pushing force", that is, the internal driving force is the spatial and regional imbalance of the world energy pattern, the external driving force is the gradual rise of new energy competitiveness, and the pushing force is the scientific and industrial revolution with the core of scientific innovation and technological progress. World energy transition has four connotations:politics, technology, management and commerce. The political synergy with the core of consultation and global cooperation mechanism is the political connotation of world energy transition; the transformation from resource-based to technology-based energy system is the technical connotation of world energy transition; the continuous improvement of intelligent level is the management connotation of world energy transition; the transformation from international oil companies to international energy companies, the business model transformation is the business connotation of the world energy transition. The pathway of world energy transition is that the international community gradually realizing the low-carbon revolution of fossil energy, the low-cost revolution of new energy and the intelligent revolution of energy management through political coordination, science and technology promotion, management driving and business pushing, promoting the transformation of the world primary energy consumption structure from fossil energy to non-fossil, clean new energy, and promoting the energy production and supply system to green, clean, efficient and safe, achieving "carbon neutral" between human energy utilization and the earth's carbon cycle system, and effectively coping with global climate change. World energy transition is an inevitable choice to achieve national and regional energy security, a new driving force to promote world economic development and economic growth, a new driving force for world GDP growth, a new force to reshape the world political pattern, an effective measure to fulfill the requirements of the Paris Agreement, achieve the goal of "carbon neutrality"in energy utilization, and cope with global climate change.China is the world's largest energy producer, consumer and carbon emitter. The proposal of development goal of "striving to reach carbon dioxide emissions at peak by 2030, and striving to achieve carbon neutrality by 2060" will accelerate the transition for fossil energy to new energy, realize the "energy revolution", ensure the security of energy supply, and promote the harmonious development of human society and the natural environment in China.

China has a complete range of coalbed methane (CBM) resources, which are extremely rich and relatively reliable. The resource foundation can completely form an emerging industry with an annual gas production of hundreds of billions of cubic meters. With strong national support, after 30 years of arduous efforts, China has made significant progresses in the exploration and development of coalbed methane, forming an industry with an annual production of 10 billion cubic meters. However, this is too far from the goal of 100 billion cubic meters of coalbed methane annually, and the national task has not been completed for three consecutive Five-year plans. At the same time, China CBM industry has lost its clear development direction. Only a small contribution can be made to the urgently needed natural gas industry in China. The fundamental reason is that the theory and technology of CBM exploration and development established domestically and internationally over the past 30 years can not fully reflect the composition and pore structure characteristics of coal, as well as the occurrence state of methane mainly in an adsorbed state, which is not fully in line with the mechanism of CBM production, of which applicability is too small to be universal. On the basis of in-depth analysis of the mechanism of coalbed methane production, it is proposed that only the integration of coal mine gas and natural gas development disciplines can establish scientific and practical theories and technologies for CBM exploration and development. Then, four types of CBM resources are divided. Moreover, each CBM resource can be established with scientific and practical theories and technologies to achieve efficient exploration and effective development. This article discusses the possibility and implementation path of building a 100 billion-cubic-meter-scale CBM industry in China from aspects such as the status of CBM resources, progress in oil and gas exploration and development technology, occurrence and migration laws of methane in coal. This article proposes to rely on the cross integration of coal and oil and gas industries, strengthen basic research, establish a theoretical and technical system suitable for efficient exploration and effective development of various types of coalbed methane reservoirs, generate a new discipline (direction), form a new production, technology, and industry field, and build a path of a large industry, To achieve the development strategy of forming an emerging coalbed methane industry supported by original theories and technologies of coalbed methane exploration and development, and to ensure the rapid formation of China's annual production of a 100 billion-cubic-meter-scale CBM industry, in order to significantly reduce China's dependence on external natural gas.

Archean buried-hill zone in the western section of Bonan low salient of Bohai Bay Basin has good conditions for hydrocarbon accumulation. Bozhong26-6 oilfield is an Archaean integrated oilfield with proven reserves of crude oil exceeding 100 million tons. Based on a large number of core, thin section, well logging and geochemical data, a systematical study was performed on Bozhong26-6 oilfield. The analysis suggests that the Archean buried-hill reservoirs can be vertically divided into weathered conglomerate zone, weathered fracture zone and bedrock zone, among which the weathered fracture zone is the key reservoir development zone. The superimposed fractures formed by the Indosinian, Yanshanian and Himalayan movements provided the foundation for the development of Archaean buried-hill reservoirs. The Indosinian compression and collision and the Yanshanian strike-slip thrust were the main driving forces for the formation of fractures, and the south-north extension of the Himalayan epoch maintained the validity of earlier fractures. Under the communication of fractures, a wide area of high-quality buried-hill reservoirs is formed by the dissolution of atmospheric fresh water, and the high-quality reservoirs are developed in the zone within 420 m away from the unconformity. The mudstone of Dongying Formation with weak overpressure and strong stability overlying buried hill provides good sealing conditions for the preservation of large-scale oil reservoirs. The Archean buried hills are in direct contact with the source rocks of Huanghekou sag in the south, and are connected with the source rocks of Bozhong sag in the north by the unconformity, thus forming a multi-dimensional oil-gas migration and charging mode. In conclusion, the above findings provide a guidance for the efficient exploration of Archean high-abundance oil reservoirs in Bozhong26-6 oilfield, further improve the hydrocarbon accumulation and reservoir mode of deep Archean buried hills in Bohai Bay Basin, and are of important guiding significance for the oil and gas exploration of the Archean buried hill zone around the southwest Bozhong sag.

Oil and gas are generated from organic matters in the rocks of sedimentary basins. Through an intensive and systematic study of global petroliferous basins, it is recognized that the distribution of global oil and gas fields is highly uneven, and most of oil and gas are enriched and accumulated in a few strata of sedimentary rocks. The distribution of oil and gas is significantly controlled by source rock, so that it is necessary to search for the source rocks initially before discovering new petroliferous basins. The nutrients required for biological growth in the sedimentary basins primarily come from rivers, and the nutrients flowing from rivers into the sedimentary basins control the degree of biological reproduction, and then control the abundance of organic matters in the source rocks, which decides the amount of oil and gas generated and the degree of enrichment of oil and gas resources in the sedimentary basins. Oil and gas are mainly distributed in the three systems on the earth, i.e., the river-lake system, river-gulf system and river-delta system. Specifically, the river-lake system is an important oil-bearing area on the earth. Lacustrine oil is mainly produced by sedimentary organic matters from the algae died in lakes. The growth of algae depends mainly on the nutrients that come from the rivers and flow into the lakes, and these nutrients can facilitate the growth of algae in the rift period and provide a guarantee for the formation of high-quality source rocks. The river-gulf system is the main distribution location of global marine oil. Gulfs are the estuary of rivers, which brings abundant minerals for rivers to promote the growth and proliferation of algae and other aquatic organisms; moreover, the gulfs are relatively isolated, which are conducive to the preservation of organic matters. In fact, boasting of the biggest reserves, the coal-type gas generated from coal-measure source rocks is the most widely distributed in the world and is mainly distributed in the river-delta system. The sediments brought by the river provide fertile soil for the growth of higher plants, and the native higher plants on the river-delta plain provide a solid material basis for the formation of coal-measure gas source rocks. The delta stratum reservoir is well developed with good reservoir-caprock configuration, which is beneficial for natural gas enrichment and accumulation.

The shale oil and gas revolution has prolonged the life cycle of oil industry in the world, and promoted the growth of global oil and gas reserves and production, thus having influences on the energy strategy of each country. The formation and evolution of organic-rich shale worldwide were controlled by the life explosion and mass extinction events in the past geological periods. In combination with the worldwide exploration and development of shale oil and gas, the shale oil and gas revolution involves scientific and technological revolution, management revolution and strategic revolution. Through the scientific and technological revolution, the resource-based view is expanded from a single resource type to a "source rock bearing oil and gas" system; the efficient and low-cost development of shale oil and gas are realized by the management revolution; a new map of the worldwide energy is reshaped by the strategic revolution. Through systematically introducing the industrial practices in terrestrial shale oil and marine/terrestrial shale gas, it is clear that the underground in-situ heating conversion technology represents the actual exploration of the large-scale development and utilization of shale oil resources with medium-low maturity, and the volume fracturing technology for horizontal well is an effective way to realize the low-cost development of shale oil resources with medium-high maturity. It is pointed out that the shale oil with medium-low maturity in the Member 7 of Yanchang Formation in Ordos Basin and that with medium-high maturity in the Daanzhai Member of Jurassic Ziliujing Formation of Sichuan Basin have great resource potential. At present, China has achieved a success in the development of marine shale gas shallower than 3500 m, and major breakthroughs have been made in the exploration of transitional and marine shale gas deeper than 3 500 m. The underground coal gasification test represents an exploration way for achieving clean and sustainable use of coal. The shale oil and gas revolution has a profound impact on China's energy development. It breaks through the traditional oil exploration theories by introducing "source rock bearing oil and gas" as a new petroleum system, drives the technological explosion, speeds up the energy type alternation, opens the development path of "depending on conventional petroleum, making a breakthrough in unconventional petroleum, and developing new energy", which is expected to achieve energy independence in China.

The genetic method with basin modeling as the core has been widely used in hydrocarbon exploration and production. China’s basin modeling theory and research are in the front ranks of countries of the world, but the application software development lags far behind other countries. According to statistics, 75 % of the 39 pieces of basin modeling software or algorithms available in China are developed by foreign companies, and 100 % of the popular software on the international market are developed by overseas companies. At present, the main challenge faced by basin modeling research is that the classical petroleum system theory widely applied in the past cannot effectively evaluate unconventional oil-gas resources. In this study, whole petroleum system theory is adopted to address the current challenges. Firstly, the basic characteristics, genetic mechanism and distribution regularities for the joint coexistence of conventional and unconventional oil-gas resources are elaborated based on the whole petroleum system theory, providing theoretical and methodological guidance for the prediction and assessment of conventional and unconventional oil-gas resources. Secondly, key technologies for predicting and assessing conventional, tight and shale oil-gas resources have been developed by establishing a combined genetic model for conventional and unconventional oil-gas reservoirs and a material balance relationship between total hydrocarbon generation and hydrocarbon resources. Thirdly, this paper establishes five sets of material balance equations between the total hydrocarbon production and the evolution and productivity of the whole petroleum system, analyzes the key geological parameters such as primitive hydrocarbon production ratio, migration-accumulation coefficient, movable hydrocarbon ratio and oil recovery, and proposes 12 key technologies of three categories for basin modeling. The new generation basin modeling system based on the whole petroleum system theory and modern information technology is expected to achieve quantitative, automated and intelligent assessment of oil-gas resources, increase the total amount of resources as the study objects by 5 to 8 times, deepen the research of predicted and assessed resources by more than 3 times, significantly improve the reliability of the predicted and assessed results, and solve the existing bottleneck problem.

Large tight sandstone gas reservoirs in Tianfu gas field of Sichuan Basin were discovered in the Member 2 of Shaximiao Formation in 2019 and the Member 1 of Shaximiao Formation in 2021, respectively. The proven reserves are 1 349×10 ⁸m ³ and the production is 15.7×10 ⁸m ³ in 2022. Based on the core and geochemical analysis data, the paper investigates the sedimentary reservoir characteristics, natural gas geochemical characteristics, gas reservoir types and gas reservoir formation conditions of Shaximiao Formation in Tianfu gas field. In the study area, shallow-water deltaic and lacustrine deposits are found in the Member 1 of Shaximiao Formation, while fluvial deposits are found in the Member 2 of Shaximiao Formation. The lithologies of the reservoir are mainly composed of feldspathic litharenite and lithic arkose, and the reservoir spaces are mainly occupied by residual intergranular pores, followed by feldspar dissolution pores. The natural gas source of reservoir is mainly from the Triassic Xujiahe Formation. The natural gas in the Member 1 of Shaximiao Formation and the 6th, 8th and 9th sand groups of 1st submember of Member 2 of Shaximiao Formation is dominated by coal-type gas with a small amount of mixed gas, while the gas in the 7th sand group of 1st submember of Member 2 of Shaximiao Formation is characterized by the occurrence of both mixed gas and oil-type gas. The gas reservoir in Shaximiao Formation of Tianfu gas field is a large lithologic gas reservoir with accumulation regularity of dual-source and multi-phase charging, fault and sandbody transport, accumulation around the source, and differential enrichment at the channel. A series of key exploration and development technologies have been developed by tackling the key exploitation problems of large tight sandstone gas reservoirs in Shaximiao Formation of Tianfu gas field, i.e., (1) technology of precisely choosing layers under the constraint of high-precision isochronous stratigraphic framework, (2) technology of finely characterizing sand bodies and precisely predicting target based on 3D seismic survey, (3) supporting technology to accelerate exploration and production based on horizontal well and volume fracturing, (4) processing technology of exploitation and transportation on the ground for the purpose of fast construction, investment, optimization and simplification, (5) integrated technical and economic template for scale and cost-effective development. The discovery of Tianfu gas field has improved the exploration and development of tight sandstone gas in China, and enriched the exploration methods of tight sandstone gas, and effectively promoted the exploration and development process of tight sandstone gas in Sichuan Basin.

China's deep coalbed methane (CBM) resources, with the burial depths exceeding 1 500 m, are abundant and coexist with adsorbed and free gases. The occurrence state, accumulation characteristics, and development laws of deep CBM differ significantly from those of mid-shallow CBM, and the unclear evolution patterns have restricted its efficient exploration and development. Taking the No.8 deep coal seam in Daning-Jixian block on the eastern margin of Ordos Basin for example, this study finely characterizes the accumulation characteristics of deep CBM and simulates the burial evolution history, thermal evolution history, and hydrocarbon generation history of deep coal seams, thus improving the deep CBM enrichment and accumulation laws and patterns; moreover, the targeted exploration and development strategies are proposed. The results show that the No.8 deep coal seam is widespread in Daning-Jixian block, with high organic matter thermal maturity and Type III kerogen. This indicates significant hydrocarbon generation potential, with the total hydrocarbon intensity of (20.2-34.7) ×10 ⁸m ³/km ². The deep coal reservoir develops cleats, fractures, texture pores, cell pores, gas pores, intergranular pores, and dissolution pores, providing favorable conditions for the accumulation of deep free-state CBM. The structural-lithologic-hydrodynamic coupling closure is favorable for the preservation of deep CBM. The evolution stages of hydrocarbon accumulation in deep coal seams in the study area include the initial hydrocarbon generation stage (Stage I, 306-251 Ma), the first thermal hydrocarbon generation stage (Stage II, 251-203 Ma), the decreasing stage of organic matter thermal evolution (Stage III, 203-145 Ma), the hydrocarbon generation peak stage (Stage IV, 145-130 Ma), and the final formation stage of the oil/gas accumulation pattern (Stage V, 130 Ma to present). The deep CBM under free and adsorbed states coexist in the study area. On this basis, the paper proposes the hydrocarbon enrichment and accumulation pattern of "wide covering hydrocarbon generation, box-type closure, microstructure adjustment, self-generation and self-storage, and blanket-type accumulation", and establishes three types of deep CBM accumulation models:microfold and physical property coupling control (Type I), microfault monocline and hydrodynamic force coupling control (Type II), and physical property and hydrodynamic force coupling control (Type III) on reservoir accumulation. These understandings can effectively guide the selection of favorable areas for deep CBM exploration in Daning-Jixian block, establish an evaluation index system for favorable areas in deep coal reservoirs, propose differentiated development plans for exploration areas with different accumulation models, and help achieve the truly efficient and low-cost development of deep CBM in the study area. The research findings have important reference significance for carrying out deep CBM exploration and development in other blocks in China.

Deep coalbed methane (CBM) will become an important field for China to increase the large-scale natural gas reserves and production in the future. It is of great significance to review the history and progress of the geological research on deep CBM propose and evaluate the existing problems and exploration directions, which can provide a reference for developing applicable exploration and development technologies. Analyses reveal that China has made three major advances in the geological research of deep CBM in the past 20 years. First, the basic concept and its scientific connotation of deep CBM have been defined. It is found that there is a critical depth for the absorbed gas content of deep coalbeds, which mainly depends on the coupling relationship between geothermal gradient and geo-stress gradient, and other geological factors can adjust the critical depth. A decrease in the adsorbed gas content may lead to an increase in free gas content, resulting in the orderly accumulation of CBM in the depth sequence and the formation of highly to super saturated reservoirs with abundant free gas in the deep coal. Second, remarkable progress has been made in research of the geological properties of deep coal reservoirs, and it has been recognized that the weakening adsorption of deep coal reservoirs and the increase of free gas content are resulted from the dynamic equilibrium between the positive effect of pressure and the negative effect of temperature. Moreover, it has been found that there is a "highly permeability window" of coal reservoirs near the transition zone of geo-stress state on the depth profile, and the formation temperature and pressure indices related to the reconstruction of deep coal reservoirs may have a threshold property, and the temperature compensation and variable pore compressibility effects may significantly lower the decay rate of permeability for deep coal reservoirs. Third, an in-depth research is gradually implemented on the accumulation and geological evaluation of deep CBM reservoirs, and the exploration on accumulation mechanism focuses on CBM gas-bearing property formed by buried depth changes, vertical permeability distribution and its geological control, thus initially revealing the "depth effect" for CBM reservoir formation. Through on-site case analysis, the relevant understandings have been deepened and expanded from basin to favorable zone, then to sweet spot and from reservoir control to production control. The analyses suggest that the organic connection and deep coupling of basic geology (reservoir-forming process), exploration geology (evaluation optimization) and development geology (dynamic process) are key directions for the geological-engineering integration in deep CBM exploration and development. Therefore, it is suggested future research should focus on "depth effect", including the systematic description of deep CBM reservoir and the characterization of gas reservoir engineering responses to geological conditions.

In terms of the"dual carbon"target, green, pollution-free and high-energy density hydrogen energy has become an important trend for the future development of energy industry. Underground hydrogen storage is a promising technology for large-scale hydrogen storage. This paper describes the concept, field practice and theoretical research status of underground hydrogen storage. A deep analysis is performed on the modes and characteristics of hydrogen storage in the salt cavern, aquifer, depleted oil and gas reservoirs, as well as abandoned coal mine, of which the advantages and disadvantages are compared from multiple perspectives. Underground natural gas storage provides technical experience for hydrogen storage, but there are obvious differences between the both. Further, the paper systematically analyzes the feasibility of underground hydrogen storage, and elaborates the difficulties and challenge in terms of caprock, wellbore integrity and chemical reaction in reservoirs. Based on the above research and analysis, the difficulties in the development of underground hydrogen storage technology are clarified; the future development prospects of underground hydrogen storage have been predicted; the corresponding countermeasures and suggestions are also put forward, such as strengthening the research on the geomechanical integrity of caprock and the integrity of wellbore, and facilitating the assessment of the geochemical and microbial reactions of reservoir rocks, fluids and hydrogen, which provide a significant reference for the underground hydrogen storage in China.

The natural gas resources in Sichuan Basin rank first in China, with the proven rate of only 18.8 % , indicating enormous potentials for exploration and development. In recent years, significant breakthroughs have been made in oil and gas exploration in new fields, new strata, and new types of marine carbonate rocks, unconventional marine gas, continental tight gas, and continental shale oil in deep to ultra-deep layers of Sichuan Basin, demonstrating tremendous resource prospects. Despite of the low degree of exploration, the marine carbonate gas reservoirs in deep to ultra-deep layers in the western and central Sichuan Basin display a 3D accumulation pattern in multiple series of strata with hydrocarbons supplied from excellent source rocks, vertically stacked and horizontally connected high-energy mound-beach reservoirs in many series of strata, good source reservoir configuration and developed fault conduit systems, which are expected to form a new trillion cubic meter scale reserve zone. The foreland subbasin-slope is a favorable area for the enrichment of continental tight gas in central-western Sichuan Basin, and two sets of petroleum accumulation systems are formed, i.e., Xujiahe Formation and the Jurassic Shaximiao Formation, in which Xujiahe Formation is the major source rock. A giant gas field of 100 billion cubic meters has been discovered with the cumulative produced geological reserves exceeding 10 ¹²m ³, and has become a new growth pole for natural gas production in Sichuan Basin. Unconventional hydrocarbon-bearing strata series such as Permian and Jurassic shale, mudstone, and coal are continuously and stably distributed. Oil and gas are widely enriched and accumulated, and most abundant in central and eastern Sichuan Basin, and moreover exploration breakthroughs have been achieved. In the favorable exploration area for unconventional natural gas, the resources in the Permian reservoirs amount to nearly 8×10 ¹²m ³; in the favorable exploration area for Jurassic shale oil, the resources are estimated to be 16.96 ×10 ¹²m ³. The marine carbonate gas and continental tight gas in deep to ultra-deep layers in the western and central Sichuan Basin have been the main area for increasing reserves on a large scale in Sichuan Basin. Unconventional natural gas and continental shale oil are important resource replacement areas.

After nearly 40 years of exploration in Kaiping sag of Pearl River Mouth Basin, a medium to large light oil field has been discovered in deep-water Paleogene strata of Kaiping11-4 structure. To further guide oil-gas exploration in Kaiping sag, the paper deeply investigates the petroleum geological conditions such as hydrocarbon sources, reservoirs, traps, preservation and migration conditions in Kaiping11-4 structure, and summarizes the oil and gas accumulation mode. The geological structure of Kaiping sag is a detachment-type compound half-graben with faults in the north and overlaps in the south. In Kaiping sag, Wenchang Formation develops high quality semi-deep to deep lacustrine source rocks with great hydrocarbon generation potential, and the shallow-water braided delta front deposits of Enping Formation develop a favorable reservoir-cap assemblage. The traps formed under the early tectonic activities are various, including faulted block, faulted anticline and plunging anticline, while the weak tectonic activity in the late period is conducive to oil and gas preservation. The inheritance faults that cut through the source rocks provide vertical migration channels so that oil and gas can be transported through the "source-fault-reservoir" system. The reservoirs in Kaiping11-4 structure have undergone multi-phase continuous charging since 17 Ma, presenting a hydrocarbon accumulation mode with the characteristics of "hydrocarbon supplying from high-quality lacustrine sources, strongly charging through near-source faults, and enriching in multiple stages and levels". The discovery of medium to large light oil field in Kaiping11-4 structure is not only a breakthrough of the new area exploration in Kaiping sag, but also a breakthrough of the Paleogene crude oil exploration in the eastern deep-water area of the South China Sea. It shows that the deep-water area of Pearl River Mouth Basin has a broad prospect for oil and gas exploration, and is of great significance to the exploration of petroliferous basins in the northern deep-water area of the South China Sea.

With the continuous integration and development of digital technologies such as big data, artificial intelligence and automated drilling technology, drilling operations are developing from automation to intelligence. Intelligent drilling technology has the functions of learning, memory and judgment. It can realize autonomous decision-making and control of some drilling operations, reduce the number of on-site operators, and greatly improve the efficiency and safety of operations. This paper introduces intelligent drilling technology and its composition, analyzes the current status and development trends of foreign intelligent drilling technology, and proposes the research direction of intelligent drilling technology based on the current status of intelligent drilling technology in China, including framework planning and standard systems, real-time measurement technology of data, and high-speed transmission technology of information, automatic control system, intelligent decision and analysis system of drilling and integrated intelligent drilling technology.

In Qiongdongnan Basin, Baodao sag is considered as the one where the strongest Cenozoic tectonic activity occurred. In 2022, China's first large deep-water and deep-layer gas field, i.e., Baodao 21-1 gas field, was discovered in Baodao 21 transition step-fault zone, thus verifying the potential of natural gas resources of Baodao sag. Based on the understanding of the basic geological characteristics of Baodao 21-1 gas field, the paper systematically analyzes the enrichment and hydrocarbon generation mechanism of source rocks, the reservoir-trap formation mechanism, the migration and accumulation mechanism of fault system, and the accumulation stages and accumulation models of natural gas of the gas field, and summarizes the groundbreaking and innovative geophysical and testing technologies for deep-water and deep-layer gas fields. Baodao 21-1 structure develops "double source" organic matter enrichment, and the intense crustal thinning leads to high heat flow in the structure, as well as accelerated thermal evolution and high gas generation intensity of source rocks; the provenance of the uplift is injected into the sag along the transition slope, forming a tectonic and lithologic trap controlled by large delta lobes; large-scale tectonic ridges are conducive to natural gas accumulation, and the differential activities of main faults and delta sandstones constitute an efficient transport system, which can provide a geological foundation for the formation of large-scale gas fields. Baodao 21-1 gas field has multi-stage oil and gas charging, proving that the transition step-fault zone develops a natural gas accumulation and enrichment mode of "enrichment in semi-enclosed environment/accelerating hydrocarbon generation at high temperature for source control, relay ramp for trap control, long-term active fault for controlling hydrocarbon migration, late multi-stage strong charging, and weak active fault for controlling accumulation". This study develops the key technologies for deep layer oil and gas geophysical exploration in the rugged seabed area of deepwater steep slope land, thus achieving the fine construction of structure and successful prediction of gas-bearing properties, and creates key technologies for safety control of flowing of deepwater and deep layer complex fluid and capacity release, thus guaranteeing the release of real production capacity of the formations. The discovery of the large gas field Baodao 21-1 has confirmed the oil and gas accumulation and enrichment mode of passive epicontinental basin with strong activity. It is believed that the relatively stable strike slope type transition zone is the "golden zone" for enrichment in medium- and large-scale gas fields. The relevant research and understanding point out the direction for natural gas exploration in Baodao sag, and have important reference and enlightenment significance for natural gas exploration in Qiongdongnan Basin, the northern and central-southern South China Sea.

Well logging is an important method for obtaining physical parameters of reservoirs, discovering and evaluating oil and gas reservoirs, and predicting oil-gas reserves. Multiple factors such as the upgrading of logging technology, development of diversified technology types, and diverse management methods of logging data have resulted in the logging information with big data characteristics such as multiple measurement types, large volume of data, and multi-source heterogeneity. The rapid development of artificial intelligence technology has provided new ideas and methods for solving the problems such as multiplicity of solutions, uncertainty in logging formation evaluation by well logging. The integration of well logging and artificial intelligence is also a new field that needs to be explored urgently. Based on systematically reviewing the research status and progress of artificial intelligence in the field of well logging, this paper focuses on the application of artificial intelligence technologies such as supervised machine learning and semi-supervised machine learning, neural network and deep learning in logging curve reconstruction, lithofacies prediction and the calculation of physical property parameters during the well logging and formation evaluation. Constrained by factors such as limited sample size, imperfect process flow, and poor self-regulation capabilities, artificial intelligence has a large development space and broad application prospects in the logging fields of fluid research and comprehensive reservoir evaluation.

Sequence stratigraphy provides not only isochronous framework for basin analysis, but also comprehensive geologic structure models for sedimentary paleogeography research as well as exploration and development of mineral deposits, and thus has been paid much attention in both academic and industry communities. Sequence stratigraphy has made rapid development in recent 30 years, especially achieving great progress in sequence formation and relevant controlled factors of continental basin, sequence stratigraphic architecture and sandbody distribution in fault depression, depression and foreland lake basin, as well as research methods of sequence stratigraphy in continental lake basin. In future, the continental lake basin stratigraphy should focus on sequence stratigraphic architecture in different types of sedimentary basins, standardized research of continental lake basin, the relations between sequence and source-sink system and shoreline migration trajectory, the relation between stratigraphic pattern and shoreline trajectory, deep sequence stratigraphy, sequence architecture, as well as numerical modelling, so as to better guide the application research on energy exploration and development.

Shale oil-gas resources are abundant in China, which have become the real alternative energies. However, there are still disputes on hydrocarbon classification system, resource assessment criteria and methods for shale oil-gas resources, thus leading to a large difference in the assessment results. By deeply analyzing the connotation, types and geological characteristics of shale oil and gas and systematically summarizing the previous research results, the paper determines the shale oil-gas classification scheme, puts forwards corresponding standard resource assessment methods, and further evaluates and analyzes the potential of shale oil-gas resources in China. The results indicate that the geological reserves of shale oil in ten major basins of China reach 318.99×10 ⁸t, and the recoverable resources are estimated to be 22.78×10 ⁸t; while those of major basins/areas in China are 65.48×10 ¹²m ³ and 13.24× 10 ¹²m ³, respectively. Shale oil resources are mainly enriched in Ordos Basin, Songliao Basin and Bohai Bay Basin, oil reservoirs are mainly distributed in the Upper Triassic, Cretaceous and Paleogene strata, respectively, within a depth of 4 500 m. Shale gas resources primarily occurred in Sichuan Basin, most of which were in the Upper Paleozoic strata at a depth over 2 000 m. Based on the assessment results and exploration practices of shale oil-gas resources, it is considered that shale oil is mainly enriched in Member 7 of Triassic Yanchang Formation in Longdong area, Jiyuan area, and Zhijing-Ansai area of Ordos Basin, as well as the Cretaceous Qingshankou Formation in Gulong sag and Sanzhao sag of Songliao Basin, the Paleogene Shahejie Formation in Dongying sag and Zhanhua sag and the Member 2 of Paleogene Kongdian Formation in Cangdong sag of Bohai Bay Basin, as well as Lucaogou Formation in Jimusaer sag and Fengcheng Formation in Mahu sag of Junggar Basin; shale gas is mainly accumulated in Changning, Weiyuan, Luzhou and West Chongqing areas in the south of Sichuan Basin.