Six sets of high-quality source rocks have been identified globally, with three of them in the pre-Mesozoic strata serving as the primary source rocks for ancient oil and gas reservoirs. Ancient oil and gas reservoirs from the pre-Mesozoic strata exhibit five key characteristics. (1) The predominant basin types include foreland, passive continental margin, and cratonic basins. (2) Their primary type of oil and gas resources remains conventional, although shale oil and gas is developing rapidly. (3) Their oil and gas accumulations are primarily concentrated in the Permian, Devonian, Carboniferous, and Ordovician. (4) Their reservoir lithology is primarily composed of limestones, sandstones, shales, and dolomites. (5) Their burial depth is predominantly within the middle to shallow layers, indicating significant potential for deep plays. The substantial discoveries of ancient oil and gas plays demonstrate enrichment in four fields: the periphery of cratons, carbonate reservoirs, shale oil and shale gas reservoirs, and basement reservoirs. After analyzing the major discoveries in key areas, it is revealed that high-quality source-reservoir-seal combinations form readily in the peripheral regions of cratons that were historically located within low-latitude intertropical convergence zones. Global significant events have played a crucial role in shaping the development of source rocks and the enrichment of shale oil and gas. Within the temporal framework of these significant global events, potential plays can be optimized in advance by reconstructing the paleo-positions of accumulation elements. Based on independent evaluations of recoverable oil and gas reserves and yet-to-be-discovered resources, it is evident that conventional oil and gas exploration should focus on the Arabian Basin, Zagros Basin, Tarim Basin, and other basins. Basement rocks and residual strata are also important potential exploration areas. For shale oil and shale gas exploration, the focus should be on the Devonian Domanik shale in the Timan-Pechora and the Volga-Ural basins in Russia, the Silurian hot shale in the Arabian Basin in the Middle East, the Silurian and Devonian plays in the Ghadames Basin in the North Africa, and several sets of shales in the Sichuan and Junggar basins in China.

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.

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.

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.

A study is performed on the reservoir-controlling of strike-slip faults in deep marine carbonate rocks (>4 500 m) in Sichuan Basin, which is of important significance for the efficient exploration and development of gas reservoirs in tight carbonate rocks. Through the analyses of gas reservoirs as well as static and seismic data, investigations are carried out on the temporal and spatial relationship between strike-slip fault and hydrocarbon accumulation, as well as the controlling effects of strike-slip fault on the gas migration, trap and enrichment. The results show that the pre-Mesozoic strike-slip fault system is dispersively distributed and widely developed in the central Sichuan Basin, which had destructive effect on hydrocarbon accumulation in the Caledonian period. However, the petroleum accumulation conditions were superior in the Indonian-Yanshanian period, thus forming the pre-Mesozoic multi-layer superimposed hydrocarbon accumulation system controlled by strike-slip faults. The strike-slip faults constitute the pre-Mesozoic vertical-lateral oil/gas transport system throughout the central Sichuan Basin. The strike-slip fault system has formed two kinds of migration modes, including the near-source lateral fault-controlled petroleum migration in the Upper Sinian-Lower Cambrian carbonate reservoirs, and the far-source vertical petroleum migration of the Middle Permian carbonate reservoirs. This has led to subsequent differentiation in stratified and zonal oil/gas accumulation. In the tight carbonate rocks, the effective structural-lithologic traps are developed under the joint action of high energy microfacies and strike-slip faults, and the both also play a role of controlling the effectiveness of traps, thus forming the gas reservoiring mode of "small gas reservoir but large field" along the strike-slip fault zones. The strike-slip faults control the distribution of the high porosity and high permeability "sweet spots" fracture-vug reservoirs and high-yield wells, which can increase the reserves, and control the hydrocarbon enrichment. The results reveal that there is a pre-Mesozoic deep carbonate strike-slip fault-controlled gas-rich system in the central Sichuan Basin, with the ternary coupling factors of "source-fault-reservoir" that control the gas accumulation; there are differences in controlling gas migration, trapping and enrichment by strike-slip faults; the strike-slip fault-controlled "sweet spot" gas reservoir is a new favorable field for exploration and development of deep carbonate rocks.

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.

After more than 10 years of theoretical innovation and engineering practice in shale gas fracturing, supporting the scale cost-effective development of marine shale gas, China has established a theoretical and technical system for marine shale gas fracturing in the middle and shallow layers (< 3 500 m). The technically recoverable resources of deep (3 500-4 500 m) and ultra deep (> 4 500 m) shale gas in China account for 56.63% of the total recoverable shale gas reserve. To achieve efficient gas exploitation is essential for the development of the shale gas industry and guarantee of oil and gas security. The recoverable resources of deep (3 500-4 500 m) and ultra deep (> 4 500 m) shale gas in Sichuan Basin and its periphery account for 65.8% of the total reserve, making the most important contribution to the efficient development of shale gas and the construction of "Daqing Gas Base". Based on the preliminary exploration and practical understanding of deep and ultra deep shale gas fracturing in China and according to the 10 characteristics of deep and ultra deep shale gas fracturing, this paper analyzes six basic problems or challenges that are derived from above situation and urgently need to be solved. Further, the paper proposes five key theories and methods that urgently need to be innovated, points out 10 development directions for deep and ultra deep shale gas fracturing, and emphasizes that China's shale gas development should focus on both deep and shallow layers and continue to improve large-scale production and EOR in the middle and shallow layers. There are both opportunities and challenges in advancing into the new fields of exploration in deep and ultra deep layers to achieve efficient development. It is still necessary to continuously enhance the research, and accelerate the establishment of China's fracturing theory and technology system for deep and ultra deep shale gas.

The upstream petroleum industry in China has achieved remarkable success. The annual crude oil production of 2×10 ⁸ t is successively achieved under difficult resources conditions, and the natural gas production has achieved rapid growth, reaching 2 200×10 ⁸m ³ in 2022. China has become the fourth largest gas producer in the world. Through exploring the exploration and development situation of oil and gas in China, this paper analyzes the theoretical and technical challenges faced by the upstream petroleum industry, and looks forward to the development prospects of domestic petroleum industry. China has realized oil-gas exploration and development in deep strata, deep water, and unconventional fields. It is predicted that China's crude oil output will be stable at 2×10 ⁸t, and natural gas production will be stable at 3 000×10 ⁸m ³ in 2035. The development of the upstream petroleum industry in China faces theoretical and technical challenges from five major fields:deep strata, deep water, unconventional resources, enhanced oil recovery (EOR) of old oil-gas fields, and carbon capture and storage(CCS) or carbon capture, utilization and storage(CCUS) projects. The future development of petroleum industry will rely more on geological theories and technological innovations in exploration of deep strata, deep water, and unconventional fields. A new generation of theories, technologies, equipment, and efficient construction teams that are suitable for deep strata, deep water, and unconventional oil-gas exploration and development are the key to achieving the high-efficiency development with low cost. The advanced technology and equipment, which are applicable for deep layer, deep water, unconventional oil and gas exploration and development, as well as EOR of old oilfields and CCS/CCUS projects, will be essential to the development of petroleum industry in the future.

A new wave of technological revolution and industrial transformation is rapidly advancing against the backdrop of global climate change, the consensus on carbon neutrality, and the imperative for energy transition. The emerging industries of new energy has become a key development focus for nations worldwide. Emerging industries symbolize the trajectory of future technological and industrial advancement. The emerging industries is growing under the leadership of established sectors innovately, while nurturing future industries and serving as a crucial direction for the development of new quality productive forces. New energy stands as a pivotal strategic emerging industry, playing a paramount role within China’s energy strategies of "cleaning up coal, stabilizing oil production, enhancing gas utilization, strengthening new energy development, promoting multi-energy complementarity, and advancing intelligent collaboration". Fueled by advancements in manufacturing, infrastructure and intelligentization capabilities, the existing energy system relied on underground resource endowments is shifting to a novel energy system grounded in technological innovation. The advancement of new quality productive forces promotes the high-quality development of emerging industries in the field of new energy. Through the synergy of technological innovation and the dual carbon goals, the "four-wheel drive" of technology innovation and carbon emissions reduction leading the way, and energy economy and security propelling the progress, will successfully resolve the "impossible triangle" contradiction that has been troubling the energy field. This transition steers towards the transformation of the energy landscape from the fossil fuel-dominated "impossible triangle" to the new energy-driven "achievable triangle", enriches and develops the "energy triangle" theory. Through a series of measures such as constructing innovation platforms, driving technological innovation, fostering collaborative innovation, developing talent teams, and constructing industrial supply chains, a group of technology leaders emerge, which will accelerate the formation of new quality productive forces in emerging industries of new energy. This effort holds the promise of transforming fossil fuels such as coal and oil into more chemical material-oriented resources, striving for new energy to achieve "technological independence", and helping China achieve "energy independence".

Offshore hydrocarbon exploration and development in China are currently in a booming stage. Extensive experience has been accumulated from oil and gas drilling operations in the shallow waters of Bohai Bay and the deep and ultra-deep waters of the South China Sea. This has led to the development of a series of key technologies suitable for offshore oil and gas drilling operations in China, laying a solid foundation for the advancement of offshore oil and gas engineering technology. Shallow-water drilling primarily focuses on the techniques such as cluster wells, horizontal wells, high-displacement wells, high-temperature and high-pressure wells, and multilateral wells; on the other hand, deepwater drilling mainly applies the deepwater shallow-depth well construction and deepwater deep-depth drilling technology. The development of fast drilling technique in Bohai Sea and the deepwater drilling operations of Well Liwan 22-1-1 in the South China Sea demonstrate the rapid advance of offshore oil and gas drilling technology in China. Shallow-water drilling technology has achieved synchronization with international standards; especially in the fields of offshore drilling riser design and installation, China holds a leading position in the world. However, the deepwater drilling technology, due to its later development, still faces certain challenges in the critical equipment including subsea wellheads, subsea blowout preventers and marine riser. To address these severe challenges and meet the future demands for the development of deep and ultra-deepwater oil and gas drilling technology, it is crucial to put more efforts in technology breakthrough and innovation in the key equipment fields.

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.

Significant breakthroughs have been made in precursor experiments for the exploration and development of deep coalbed methane, showing good prospect for development. However, deep coalbed methane has relatively high buried depth with strong heterogeneity. Lots of geological and engineering factors may affect the development results, and reasonable development countermeasures are still not determined. This paper is a case study of No. 8 coal seam in Ordos Basin, and analyzes its accumulation laws and development characteristics. The results show that No.8 coal seam has high maturity, stable distribution in the whole basin, and huge hydrocarbon generation potential; the average volume proportions of micropores, mesopores, macropores, and microfractures in deep coal reservoirs are 78.0%, 6.8%, 2.1% and 13.1%, respectively, as being a typical multiple pore-fracture system with superior hydrocarbon accumulation conditions; deep coalbed methane is located below the critical depth, characterized with a small-scale structural uplift, relatively tight reservoirs, undeveloped faults, weak hydrodynamic forces, and better preservation conditions. There is a high content of deep coalbed methane in the study area, which coexists with adsorbed gas and free gas. The coal structure is generally well developed, which is more conducive to reservoir stimulation by hydraulic fracturing. The production of gas wells quickly increases at early stag, characterized with high early production and rapid decline; according to desorption laws, the whole process can be divided into three development stages:free gas production, stable production, and decline. To address the challenges faced in the exploitation of deep coalbed methane, based on the experiences obtained during the development of tight gas and shale gas, four targeted suggestions are proposed:(1) initially applying 3D seismic technique; (2) establishing a reservoir geomechanical model; (3) building an industrialized large-scale well cluster construction mode; (4) keep doing precursor experiments. Finally, taking the Daning-Jixian block as an example, the understandings obtained from the precursor experiments have been summarized, will provide reference for further development of deep coalbed methane.

The ultra-deep oil and gas resources are abundant in China’s superimposed basins, which are an important strategic replacement field. The exploration and research work has revealed that there is a dichotomy of accumulation conditions for ultra-deep oil and gas reservoirs; favorable accumulation conditions only exist in specific basin environments, characterized with regionality, while the unfavorable accumulation conditions are inherent attributes of ultra-deep layers, characterized with universality. The decisive factors determining whether ultra-deep layers have exploration value are the effectiveness and scale of source kitchens, the effective reservoir and its scale, as well as the spatial combination and effectiveness of source, reservoir, and cap. The basins with exploration potential in ultra-deep layers have the following characteristics: (1) there is differential subsidence evolution in cratons, which have not been deeply buried during a long geological history, and where source kitchens are developed and still in an effective hydrocarbon-generation window to this day; (2) sedimentary strata mainly composed of carbonate rocks are developed, with granular platform marginal-platform shoals and intraplatform shoals, and have undergone constructive diagenesis and modification, or have experienced groundwater dissolution and leaching during geological history, as result of which reservoirs with pores in ultra-deep layers (including fractures and caves) are developed and have been effective till today; (3) the development of clastic rock, basement, or volcanic reservoirs requires a combination of single or multiple factors, such as long-term shallow burial and later deep burial with a short burial time, the presence of structural bridges for supporting effect, less compaction, the generation of fractures by tectonism, or long-term weathering for constructive reformation of crystalline rocks; (4) the basin generally presents a medium to low geothermal field, or there is no excessive radioactive material in the environment during the development of source rock, and the large-scale hydrocarbon generation is not accelerated. The reasons for the occurrence of unfavorable accumulation conditions in ultra-deep layers include: (1) mechanical compaction and high temperature and pressure result in strong diagenesis and increased plasticity of rock particles in ultra-deep layers, which is not favorable to the preservation of reservoir pore space; (2) most source rocks in ultra-deep layers have lost their hydrocarbon-generation potential, and the effectiveness of source kitchens is limited due to deep burial and long burial history; (3) there is a low probability for forming an effective combination of source-reservoir-seal-trap, and the probability of economic resource mineralization is reduced. China has abundant oil and gas resources and great exploration potential in ultra-deep layers, but large-scale exploration faces challenges in terms of the hydrocarbon accumulation theory to be perfected and engineering technology, and it is urgent to carry out researches to achieve relevant breakthroughs.

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.

Ordos Basin is rich in oil-gas resources and now is the largest oil-gas production base in China. With the continuously growing energy demand of the country, Ordos Basin has played the main role in increasing reserves and production. In recent years, based on the innovation in geological theory and breakthrough in key technology, major breakthroughs and significant progress have been made in new fields and new types of oil exploration in Ordos Basin. The paper reviews the four fields of shale oil area, Tianhuan depression-western margin thrust belt, Sanbian areas (Jingbian-Dingbian-Anbian areas), and the lower assemblage of Yanchang Formation, and analyzes their geological conditions, exploration progress, and resource potential. On this basis, the key insights were obtained as below. (1) Shale oil is expected to be the main contributor for the sustainable development of production above 6 000×10 ⁴t in Changqing oilfield. Ordos Basin develops continental shale oil in the Member 7 and 9 of Mesozoic Yanchang Formation, as well as marine shale oil in Paleozoic Wulalike Formation. Specifically, the interbedded shale oil in the Member 7 of Yanchang Formation has the proven reserves of 40.5×10 ⁸t, which is the main target for exploration and development; the laminated shale oil has an estimated resource potential of 20×10 ⁸t, achieving a strategic breakthrough; the breakthrough test for lamellar shale oil is steadily promoted, and its success will have a revolutionary impact. The Member 9 of Yanchang Formation in northern Shaanxi area develops "Lijiapan shale", and the risk exploration of shale oil is progressing smoothly. The exploration in Wulalike Formation in the southern section of the western margin of the basin has a good start, and new strata are exploited in the exploration of Paleozoic marine shale oil. (2) New oil enrichment areas are detected in the complex tectonic zone of Tianhuan depression and western margin thrust belt, forming three replacement areas: Yujialiang, West Huanxian, and North Pingliang, with the resource potential of more than 5×10 ⁸t. (3) New progress has been made in multi-strata and three-dimensional exploration in Sanbian areas, and the Haotan Integrated Demonstration Zone has been quickly built. The resource potential of Sanbian areas is preliminarily estimated as 5×10 ⁸t. (4) The lower assemblage of Yanchang Formation shows a good exploration prospect. Multiple favorable areas have been discovered through outstepping exploration in the Member 9 and 10 of Yanchang Formation, with the proven reserves of nearly 3×10 ⁸t. Overall, Ordos Basin is in the middle stage of exploration and still has great potential for increasing reserves. The new fields and types of oil exploration will provide replacement resources for oil companies to implement the important strategies of high-quality petroleum development.

Since establishing the Da’an circulation block in western Chongqing in June 2021, Zhejiang oilfield has been making every effort to increase and accelerate the exploration and evaluation of deep shale gas, as well as implementation work, and constantly deepen geological understanding and improve engineering technology. Thus, industrial breakthroughs have been achieved in the production tests of multiple wells, and the Da’an deep shale gas field was discovered in western Chongqing. Through systematically introducing the exploration and discovery process of the Da’an block in western Chongqing in the past two years, the paper comprehensively analyzes the geological accumulation conditions in terms of regional geological characteristics, sedimentary lithofacies, organic geochemistry, pores and fractures, physical properties, gas-bearing properties, fracture characteristics, geological and mechanical properties of rock, as well as high-quality reservoir distribution characteristics, and also summarizes the key techniques for the exploration and development of deep shale gas in Da’an block, which have been formed through practice and innovation. Da’an block was the depocenter of the Upper Yangtze foreland basin at the northern foot of the Jiangnan-Xuefeng Caledonian orogenic belt during the sedimentary period of the submember 1 of Member 1 of Wufeng-Longmaxi formations. The high-quality shale layer in the lower section was of deep-water shelf facies, and the strong reduction and anaerobic environment provided good source and reservoir conditions. As a result, the organic carbon-rich siliceous shale was developed; this block possesses excellent organic geochemical indicators, well-developed micro-reservoir space, good physical properties, good self-sealing property of shale, and high gas-bearing properties, indicating an overpressure continuous shale gas reservoir with over-matured dry gas. Based on the good conditions of shale roof and floor and the deformation of comb-shaped fold structure, an enrichment and accumulation model has been built for the deep shale gas (burial depth of 3 500-4 500 m) in western Chongqing based on the characteristics of "narrow steep anticlinal faults as the barrier bed and contiguous widely-distributed gentle synclines, hydrocarbon enrichment and high production in tectonic transition belt and low-amplitude anticline structure", reflecting the theoretical connotation of enrichment, accumulation and occurrence of mountainous shale gas under the mode of "multi-field synergy, multi-element coupling, multi-factor superposition". Through practical exploration, five comprehensive evaluation methods and technologies have been developed for the exploration and development of deep shale gas in Da’an block, including the fine identification and stability evaluation technology of multi-scale natural fractures, the integrated evaluation and design technology for the full life cycle of well platforms, the matching technology of safe, excellent and fast drilling under high temperature, the segmented volume fracturing 2.0 technology for horizontal wells that focuses on increasing reserves and production under the control of dense crushed fractures while preventing casing deformation, and the fine pressure control and flowback technology for deep shale gas based on continuous monitoring of high-frequency pressure and dynamic evaluation optimization of artificial gas reservoirs. The exploration and discovery of Da’an deep shale gas field the western Chongqing has further promoted the rapid development of deep-ultra deep marine shale gas in China.

Shale oil and gas resources currently spurt into popularity worldwide in the field of unconventional oil and gas exploration and development, of which industrial production can be effectively achieved by hydraulic fracturing. Based on the physical characteristics of shale reservoirs and the rheological properties of fracturing fluids, the technological progress, in stimulating shale oil and gas reservoirs in the United States, is systematically summarized, involving the understanding of fracture-controlled reservoirs, hydraulic fracturing monitoring technology, refracturing technique, data platform construction, and field-test site establishment. Additionally, seven key technologies were achieved during shale reservoir stimulation in China, including fracture-controlled stimulation techniques, innovative matched hydraulic fracturing equipment, core tools for multi-stage hydraulic fracturing, low-cost hydraulic fracturing materials, hydraulic fracture monitoring technology, wellbore reconstruction hydraulic fracturing technology, and fracturing optimization design software. Technical challenges faced by shale oil and gas reservoir stimulation are comprehensively analyzed in four areas:effective identification of sweet spots, optimization of hydraulic fracturing parameters, three-dimensional recovery of reserves, and potential exploitation of remaining reserves. On this basis, in order to effectively improve the development of shale oil and gas resources by fracture networks and realize large-scale production and cost-effective development of shale reservoirs, four development suggestions are put forward:(1)strengthen basic research to lay a solid foundation for the large-scale development of shale oil and gas; (2)enhance technological support to build a Chinese special hydraulic fracturing technology system; (3)increase reserve recovery rates and establish a full-life-cycle technology system; (4)promote digital transformation and establish an intelligent development pattern of the Internet of Things.

The light oil from Gulong shale is widely distributed, with favorable components and temperature-pressure conditions for miscibility with CO ₂. Pre-fracturing with CO ₂ injection and huff-and-puff can offer significant potential to enhance oil recovery. However, there is a lack of sufficient understanding of the high-pressure phase behavior of Gulong shale oil. Based on the equation of state and two-phase equilibrium theory, through verifying the results of constant mass expansion experiment and slim tube experiment for shale oil, the paper establishes a thermodynamic oil-CO ₂ two-phase equilibrium model considering the nano-confinement effect, and also a calculation method for the minimum miscibility pressure based on the two-phase equilibrium model. This paper is a case study of Gulong shale oils in Well Guye 2HC and Well Guye 9HC, and elucidates the interphase mass transfer behavior of Gulong shale oil and CO ₂, which is influenced by the factors such as maturity, oil/CO ₂ ratio, pressure, and nano-confinement effect. The results show that with an increase in CO ₂ mole fraction, the saturation pressure of Well Guye 2HC and Well Guye 9HC shale oils gradually decreases. Under reservoir temperature and pressure conditions, both Well Guye 2HC and Well Guye 9HC shale oils can be miscible with CO ₂. Under the same amount of CO ₂ injection, Well Guye 2HC shale oil exhibits a higher molecular weight and viscosity with a greater drop, and a lower saturation pressure and expansion coefficient with a smaller variation than Well Guye 9HC shale oil. The multilevel contact process of CO ₂ injection shows that the dissolution capacity and extraction effect of CO ₂ are similar in both Well Guye 2HC and Well Guye 9HC shale oils. After sufficient contact, C ₁-C ₆ components in the oil phase of Well Guye 2HC and Well Guye 9HC shale oils at the far end opposite to injection gas front are all extracted into the gas phase, and the mole fractions of CO ₂ in the oil phase increase to 86.63 % and 87.35 %, respectively. The presence of nano-confinement effect reduces the compositional differences between oil and gas inside nanopores, leading to a decrease in the interfacial tension and minimum miscibility pressure, which is beneficial to the mutual dissolution and miscibility between CO ₂ and shale oil. The impact of the nano-confinement effect on Well Guye 2HC and Well Guye 9HC shale oils is not significantly different. When the pore radius decreases from 100 nm to 10 nm, the minimum miscibility pressure of Well Guye 2HC and Well Guye 9HC shale oils with CO ₂ is decreased by 20.90 % and 21.31 %, respectively. Understanding the phase behavior of fluids in shale oil reservoirs can provide a theoretical guidance for the optimization of CO ₂ injection development.

Well Xiongtan 1 in Kalayuergun structural belt of western Tabei uplift, Tarim Basin, has made a major breakthrough in oil and gas exploration in the Upper Cambrian Xiaqiulitage Formation in September 2023. This is another significant oil bearing strata discovery that has been made since Cretaceous and Paleogene in Tabei area, demonstrating the three-dimensional multi-layer hydrocarbon accumulation in Tabei area. Based on comprehensively analyzing the structural styles, fault characteristics, as well as the drilling, logging and testing data of Well Xiongtan 1, the paper makes clear the source rock conditions, oil and gas channel, reservoir-cap conditions and trap types of Kalayuergun structural belt, and systematically summarizes the accumulation elements and modes of the Cambrian Xiaqiulitage Formation in Kalayuergun structural belt. Two sets of deep source rocks are developed in Tabei uplift. The hydrocarbon source correlation shows that the Cambrian Yuertusi Formation is the main source rock layer, and the potential source rock is developed in the pre-Cambrian rift trough. Tectonic movement is active in the study area, forming Caledonian, Hercynian and Himalayan faults. NNW-trending strike-slip faults are superimposed with NW- and EW-trending thrust faults, forming an interlaced fault system, which vertically communicates with deep source rocks and reservoirs. Traps of the Upper Cambrian Xiaqiulitage Formation were formed at an early stage, where multiple periods of oil and gas accumulation occurred; under the influence of strong compression in Late Hercynian period, several faults connected with source rocks and related structural traps were initially formed. As a result of the late tectonic movement, the whole area continued to uplift, and formed a large area of continuously distributed tectonic traps in the Upper Cambrian reservoir, capturing oil and gas in multiple stages. The hydrocarbon accumulation mode of "lower generation and upper reservoir, dredging by faults and near-source accumulation" is established. The research results reveal that the Cambrian Xiaqiulitage Formation in western Tabei uplift has a huge exploration prospect, and it is expected to become a new strategic replacement area for increasing reserve and production in the platform area of Tarim Basin.

China is rich in deep oil-gas resources, showing a great exploration potential. The exploration history of deep reservoirs as well as oil-gas exploration practice indicate that geophysical techniques play an extremely important role. Focusing on key challenges such as large burial depth, weak seismic reflection energy, low imaging accuracy and complex reservoirs in the deep target strata, scientific research and technical breakthroughs have been performed and made on seismic equipment, acquisition, processing and interpretation, as well as gravity-magnetic-electric-seismic joint exploration, thus forming a set of seismic technologies for deep oil-gas exploration. Extensive practices have shown that the large-tonnage broadband vibroseis is an important technique for improving deep seismic signal energy and signal-to-noise ratio, the "broadband, wide azimuth and high density" (BWH)seismic acquisition technology is an effective way to achieve the target for deep oil and gas exploration; weak signal processing, complex structure imaging, and 5D seismic interpretation technique are key processing and interpretation techniques to solve all problems in deep exploration. Moreover, the combination of multiple physical fields, such as gravity, magnetism, electricity and seismic exploration, is an efficient method to reduce the risk of deep exploration and development. These geophysical techniques have been successfully applied in some basins in China, such as Tarim Basin and Sichuan Basin, which have provided supports for making major breakthroughs such as the discovery of 1 billion-ton gas field in Fuman area of Tarim Basin, and a trillion cubic meter gas area in Penglai area of the north slope of central Sichuan Basin. Facing the current and future demands for geological research, discoveries in hydrocarbon exploration, safe and efficient drilling during deep exploration, it is recommended to continuously make breakthroughs in five aspects, i.e., basic theory, acquisition, processing, target identification, wellbore seismic and non-seismic techniques, actively expand the exploration fields of deep to ultra-deep oil and gas, and carry out research and on-site experiments of marine geophysical exploration technology based on ocean bottom node (OBN), thus providing technical support for deep sea exploration.