The types and configurations of source-reservoir coupling can be identified based on the shale oil and gas source-reservoir coupling, which provides a basis for the determination of ideas about shale oil and gas exploration and the efficient exploration and development of shale oil and gas. However, until now, shale oil and gas have not introduced by any scholars into a unified evaluation system for the classification of source-reservoir coupling types, which to some extent restricts the exploration and development process of shale oil and gas. In view of this, based on analyzing the source-reservoir configuration characteristics of typical marine and terrestrial shale oil and gas reservoirs in China, the source-reservoir coupling relationship of shale oil and gas is divided into three categories. Moreover, this study makes clear the geological connotations of different source-reservoir coupling types and their mechanisms controlling oil and gas enrichment, and proposes an efficient exploration approach based on the overall evaluation of shale oil and gas in China. The research results suggest that the source-reservoir coupling types of shale oil and gas can be divided into three categories: source-reservoir separation, source-reservoir coexistence, and source-reservoir integration. Specifically, the migration distance of source-reservoir separation hydrocarbons is above meter scale, and the near-source oil and gas forms sweet spots, represented by the Lower Cambrian Qiongzhusi Formation in Sichuan Basin, the first and second submembers of Member 7 of Triassic Yanchang Formation in Ordos Basin, and the Permian Lucaogou Formation in Jimusar sag of Junggar Basin. The source-reservoir coexistence is characterized with the multi-source supply of hydrocarbons and the coexistence of source and reservoir, of which hydrocarbons are migrated into the nearby advantageous reservoirs to make them oil-bearing as a whole, represented by the Member 2 of Permian Wujiaping Formation in Sichuan Basin, the Jurassic Lianggaoshan Formation in Sichuan Basin, and the Member 4 of Paleogene Shahejie Formation in Jiyang depression of Bohai Bay Basin. The source-reservoir integration indicates that the source rock and reservoir are in the same stratum, and hydrocarbons undergo micro migration within the stratum, represented by the Ordovician Wufeng Formation and Silurian Longmaxi Formation in Sichuan Basin and the Cretaceous Qingshankou Formation in Songliao Basin. Sedimentary environment, biogenic silica, thermal maturity, and hydrocarbon generation/expulsion efficiency are the core elements that affect the shale oil and gas source-reservoir configuration and furtherly control the enrichment of shale oil and gas. Taking the typical shale oil and gas reservoirs in China as an example, the paper furtherly clarifies the exploration levels and ideas under the vertical multi-type source-reservoir coupling configuration at different levels of maturity. The research results are beneficial for quickly identifying and optimizing favorable intervals of shale oil and gas, providing an important scientific basis for the efficient exploration and development of shale oil and gas in China.

Currently, sweet spot evaluation plays an important role in unconventional oil and gas exploration and development, which is of great significance to the large-scale efficient development of unconventional oil and gas. The concept connotation of sweet spot has been increasingly expanded and more diversified and regional the corresponding evaluation parameters and standard values are more diversified and regionally distinctive. At present, the commonly-used sweet spot evaluation and prediction methods include the contour map semi-quantitative plane superimposition evaluation method, the sweet spot quantitative and semi-quantitative evaluation method based on multi-parameter co-constraint, the radar graphic method, and the sweet spots quantitative evaluation method established based on the geological anomaly theory. In the practical application, the applicability evaluation and prediction method should be developed according to the basic data such as tectonic depositional settings, lithological association and resource type of the basin, and the principle of superposed progressive discrimination. Continental shales in China are highly heterogeneous, and there is a significant difference in the enrichment laws and main controlling factors of different types of shale oil. Both interlayer and hybrid shale oil have experienced migration and accumulation in the source. The main lithology of the reservoir is sandstone (siltstone) and carbonate rock (hybrid sedimentary rock). The reservoir property, hydrocarbon potential and brittleness of reservoirs are the key indicators. The pure shale oil intervals in the thick and ultra-thick layers is generally oil-bearing, and the oil is mainly retained in the source. The source rocks are the reservoirs. It is suggested to use the trichotomy method to divide hydrocarbon enrichment layers into Type I, Type II and Type III using 5~8 key parameters based on the data of sedimentary cycle, laminated texture type, lithological association, hydrocarbon potential, reservoir property, compressibility, mobility and recoverability. During the optimization of enrichment layers, zoning should be planned according to the thermal evolution maturity of different basins and zones. In the medium-low maturity zone, the medium-high TOC content shale interval (felsic laminae develop) adjacent to the high TOC content shale interval should be optimized; in the medium-high maturity zone, the high TOC content shale interval should be optimized. As the "gold target layer", Type I oil reservoir should be developed and produced initially, and progressively exploited according to technological maturity, so as to realize the maximum development and utilization of China's continental shale oil resources, and effectively serve to guarantee the national energy security.

As the super and most petroliferous basin in China, Songliao Basin has achieved strategic breakthroughs in the exploration and evaluation of Gulong shale oil, of which the potential and scale of resources remain unclear. Based on the extensive geochemical data including total organic carbon (TOC), rock pyrolysis, vitrinite reflectance and pressure-reserved core, in combination with logging and production data, a systematic evaluation was conducted on various types of shale oil, primarily in Qijia-Gulong sag. A classification scheme using organic matter maturity and reservoir type as key indicators was developed for shale oil in Songliao Basin. As a result, grading standards for shale oil were established based on the key parameters such as TOC content, oil content, effective porosity, and oil saturation. A shale oil resource evaluation method was created, involving the key technologies such as precise evaluation of oil content, light hydrocarbon recovery and calibration of recoverable coefficient. Based on dynamic production data, the geological resource potential of shale oil under current technological conditions was assessed, achieving the predictive analysis of resource recoverability. The comprehensive evaluation indicates that Qijia-Gulong sag contains medium- to high-maturity shale oil resources of 107.73×10 ⁸t (including 42.08×10 ⁸t of Class Ⅰ resources and 33.67×10 ⁸t of Class Ⅱ resources), with technically recoverable resources exceeding 8×10 ⁸t. Additionally, the geological resources of dissolved gas are estimated to be 1.75×10 ¹²m ³, and the technically recoverable resources amount to 0.13×10 ¹²m ³. The resource evaluation results suggest that the favorable shale oil resources in Songliao Basin are mainly distributed in Qijia-Gulong sag, as being the essential strategic replacement resource. With future advancements in development technologies, the recoverable potential of shale oil is expected to increase significantly.

The Cambrian Qiongzhusi Formation is one of the earliest series of strata for shale gas exploration and research in China. In the early stage, due to unclear understandings of the overall geological cognition and limited technological conditions, a number of wells were only deployed in the Weiyuan anticline and Changning anticline with a burial depth less than 3 500 m and a relatively gentle structure. The production rate of the wells is low, indicating a failure in the large-scale commercial development. Recently, major exploration breakthroughs have been made in Well Zi201 and Well Weiye1H, marking significant progress in geological cognition of the deep shale gas in Qiongzhusi Formation of the Deyang-Anyue aulacogen. The sedimentary environment of Qiongzhusi Formation is controlled by the aulacogen. The deep-water siliceous argillaceous shelf facies in the trough and deep-water silty argillaceous shelf facies on the slope of the trough edge are the dominant sedimentary facies zones, which are conducive to the enrichment and accumulation of shale gas. Vertically, Qiongzhusi Formation has developed multiple sets of shale reservoirs, mainly consisting of the 1st, 3rd, 5th, and 7th substrata. In particular, the 5th substratum is a key breakthrough layer with the total organic carbon content of 2.7% to 3.1%, porosity of 4.2% to 4.9%, brittle mineral content of 69.5% to 76.5%, gas content of 7.8 m ³/t to 9.5 m ³/t, and moderate maturity of 3.0% to 3.5%. The 3rd substratum is a potential exploration stratum. Qiongzhusi Formation is expected to realize multi-interval three-dimensional development. The bottom margin of the Cambrian System has a simple structure in the middle section of the aulacogen, lacking of obvious major faults. The pressure coefficient of Qiongzhusi Formation is generally above 1.8, and the preservation conditions are favorable. The aulacogen provides sufficient sedimentary space and material basis, as a result of which the shale in Qiongzhusi Formation is rich in hydrocarbon sources and has achieved a high volume of gas production; the existence of Leshan-Longnüsi paleo-uplift prevents the shale in Qiongzhusi Formation from excessive thermal evolution. A "aulacogen-paleouplift" shale gas enrichment model has been established, and it has been determined that the favorable exploration area of Qiongzhusi Formation is 4 400 km ² and the resources amounts to 2×10 ¹²m ³. The exploration breakthrough of shale gas in Qiongzhusi Formation has opened up another new field for achieving a trillion of cubic meters of reserves and a billion of cubic meters of production. Next, the geological-engineering integrated high-yield model of Well Zi201 will be promoted and applied to the exploration and development fields of marine deep and ultra-deep shale gas in the entire Upper Yangtze area of southern China.

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.

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.

Heavy oil is an important type of oil resources. Sustainable and efficient development of heavy oil resources have great significance to national energy security. The main characteristics of thermal recovery of heavy oil in China are summarized as below:as viewed from geological and oil-reservoir characteristics, China boasts various types of heavy oil reservoirs with deep burial, thin bed, strong heterogeneity and complex oil-water system; as for composition, the spatial reticular structure formed from the interaction between colloid and asphaltene molecules leads to high viscosity of heavy oil; as for rheological properties, there is a critical temperature. When the temperature is higher than the critical temperature, heavy oil displays the properties of Newtonian fluids; when the temperature is lower than the critical temperature, heavy oil displays the rheological properties of Bingham fluids with yield value; as for percolation characteristics, heavy oil possesses the properties of underground non-Darcy flow, with a starting pressure gradient, and it is subject to the influences of temperature, reservoir permeability, crude oil viscosity and asphaltene content. This paper summarizes the status quo of heavy oil development technology at home and abroad, and elaborates the main mechanism, applicable conditions, application examples, current problems and development direction of steam huff and puff, steam flooding, steam assisted gravity drainage (SAGD), in situ combustion and thermal composite development. Steam huff and puff is still the main method for thermal recovery of heavy oil and steam flooding is one of the effective substituted techniques to steam huff and puff; SAGD has made important progress in technology introduction and absorption; in situ combustion has become an important technology of greatly improving recovery efficiency; thermal composite development technology has realized efficient production of the marginal heavy oil. It is indicated that heavy oil requires high-quality and efficient thermal recovery technology in the future. In line with the maximization of "double objectives" for recovery efficiency and oil steam ratio, it is required to continuously strengthen reservoir description, dynamic monitoring and injection-production regulation, and actively explore the transformation of heat generation mode, so as to realize efficient development of heavy oil and green low-carbon development.

The Whole Petroleum System theory establishes the unified accumulation mechanism, enrichment regularity and geodynamic control conditions of conventional and unconventional oil and gas. Tight oil and gas are crucial components of the Whole Petroleum System. This paper reviews the development history of tight oil and gas, looks forward to the resource prospect of tight oil and gas, describes the geological characteristics of typical tight oil and gas reservoirs in China, and reveals the accumulation mechanism and enrichment regularity of tight oil and gas from the perspective of the Whole Petroleum System theory. The research results are as follows. (1) China’s tight oil and gas resources have broad prospects and great development potential, and great achievements have been made in the field of exploration and development, but there are still great challenges in the future, including geological theory, engineering technology and enhanced oil recovery technology. (2) Both physical property and accumulation process of tight oil and gas reservoir are between those of conventional oil-gas and shale oil-gas. The complex capillary network composed of pore throats within the tight reservoir is the key to the self-containment of tight oil and gas. (3) Oil and gas resources in different petroliferous basins in China show distinct differential enrichment characteristics. The Ordos Basin is a super tight oil and gas enrichment basin. (4) Based on the source-reservoir coupling relationship, tight oil and gas reservoirs can be classified into far-source type, near-source type, and intra-source type.

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.

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.

The evaluation of oil and gas resources is to predict the potential of oil and gas resources in the future based on the understanding and judgement of the geological conditions of hydrocarbon accumulation,which is of great significance for oil companies to implement the internationalization strategy.According to the evaluation methods,petroleum geological theories,exploration technologies,and types of discovered traps,the development history of global oil and gas resources evaluation can be divided into four stages:start-up (1900-1957),rapid development (1958-1985),stable development (1986-2007) and participation by China (2008-).The evaluation results of global oil and gas resources are affected by the evaluation methods used at different stages,the evaluation scope of resources,petroleum geological theories,exploration technologies such as geophysics and drilling,as well as oil price,and hydrocarbon production.After comparing and analyzing the evaluation or statistical results of global oil and gas resources of China National Petroleum Corporation (CNPC) in 2020,the United States Geological Survey (USGS) in 2012 and the International Energy Agency (IEA) in 2019,it is considered that the evaluation results of CNPC (2020) is more comprehensive,and the evaluation results of recoverable resources to be discovered are lower than those of IEA (2019).With the development of petroleum geological theories and the progress of science and technology,oil and gas resources will be continuously transformed into petroleum reserves and production in the future.The evaluation methods of global oil and gas resources will gradually focus on the overall evaluation of source rock as the core object,the evaluation results will be presented in a three-dimensional way,the evaluation objects will continuously expand to deep water,deep play and unconventional resources,the evaluation process will highlight the requirements in terms of "economy" and "low carbon" ;big data and artificial intelligence technology will also play an important role in the future evaluation of global oil and gas resources.

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.

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.

As a type of unconventional oil and gas resources, shale oil and gas are self-generated and self-preserved. Divided according to the thermal maturity, medium-high maturity and medium-low maturity shale oil can be obtained; when divided according to the depositional environment of shale, marine, transitional and lacustrine facies shale gas are obtained. China is one of the most successful countries that have achieved large-scale commercial development of continental shale oil in the world. Significant discoveries of continental shale oil have been made successively in the Ordos Basin, Junggar Basin, Songliao Basin and Bohai Bay Basin. The marine shale gas industry has achieved breakthroughs and rapid scale development in the Sichuan Basin and surrounding areas. By the end of 2021, a total of 8 shale gas fields had been found in southern China, with the proved geological reserves totaling 2.74×10 ¹²m ³. In 2021, the annual production capacity of shale gas was 230×10 ⁸m ³, bringing the total production capacity to 924×10 ⁸m ³. The shale oil and gas resources in China have great potential, but there are many challenges during the large-scale exploration and beneficial development. Based on the development experience of shale oil and gas in foreign countries and relevant inspirations, it is suggested that the state takes the lead in evaluating and implementing the technologies that can convert black shales or high-carbon coals into oil and gas, estimating the total amount of economic resources involved, and formulating corresponding development plans. Additionally, national pilot test areas should be set up for in-situ conversion of black shales and high-carbon coals into oil and gas, and fiscal incentives and tax support policies for the conversion of shales and coals into oil and gas should be introduced and implemented to promote the maturity and conversion of underground shales and the heated conversion of underground coals into oil and gas. Moreover, national top-level design and coordinated investment should be implemented to establish the base of "worldwide super energy basins" represented by Ordos Basin and Sichuan Basin, so as to achieve the collaborative and integrated development of underground and overground resources such as renewable energy sources on the ground and oil, gas, coal, heat, lithium and uranium resource under the ground, involving CO ₂ capture and storage (CCS) and CO ₂ capture, utilization and storage (CCUS).

The production measures of oil and gas field development is severely restricted by the degree of understanding of subsurface reservoirs and fluids; reservoir description plays an important role in oil and gas field development business, and the main goal of reservoir description is to construct the digital twin system of reservoirs. Based on analyzing the current research status and development trend of oil and gas field development and the demands for digital transformation-based production, the paper proposes the digital twin theory of oil and gas reservoir, which defines the reservoir digital twin as "building a digital twin simulation model of oil and gas reservoirs to maximize the quantitative approximation of the real reservoir, characterizing the dynamic changes of the whole life cycle of reservoirs in a timely and accurate manner, and simulating the development behavior of reservoir entities from the physical world in a real environment". This points out the direction for the integrated research of reservoir description and reservoir engineering. Further, the paper presents the key directions and contents of smart oil and gas field construction based on the digital twin system of oil and gas reservoirs, and it is pointed out that by establishing a digital copy of oil and gas reservoir development system, i.e., the digital twin system of oil and gas reservoirs, as a basis for optimal development and scientific management of oil and gas fields in the cloud, a new technological revolution in the field of oil and gas field development will emerge, and the digital twin system of oil and gas reservoirs will give new connotation to the construction of smart oil and gas fields.

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".

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.

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.

After more than ten years of exploration and practice, a series of progress has been made in marine shale gas exploration in Sichuan Basin. During that period, focusing on Wufeng-Longmaxi formations as the most favorable pay zone, a few theories for the enrichment and high production of shale gas were proposed, the exploration and development technologies integrating geological evaluation, development optimization, optimal-fast drilling, volume fracturing, factory operation and clean exploitation was formed, and a large shale gas field with reserves of one trillion cubic meters was proved. At an important time for the development of shale gas exploration in China, it is of great significance to promote the exploration and development of marine shale gas by reviewing the exploration and development history of marine shale gas, summarizing the achievements and knowledge of shale gas in Wufeng-Longmaxi formations in terms of geological conditions and enrichment laws, and making an outlook on the key replacement fields for marine shale gas exploration in Sichuan Basin. (1) The exploration and development of marine shale gas in Sichuan Basin have gone through four stages:layer and zone evaluation stage to find the target; pilot test stage of shallow to medium-deep reservoir; demonstration zone construction stage of shallow to medium-deep reservoir; stage of shallow to medium-deep reservoir production, deep reservoir evaluation, non-pressurized shale gas evaluation, three-dimensional development evaluation, ultra-deep and new reservoir exploration. (2) The sedimentary conditions of the Wufeng-Longmaxi formations in Sichuan Basin are superior, in which the deepwater shelf shales with high organic content are continuously and stably distributed. Shale gas mainly occurs in organic matter pores, and its reservoirs are concentrated longitudinally with large continuous thickness. The structures are relatively simple in the southern Sichuan Basin and the Fuling block of southeastern Sichuan Basin. The conditions for shale gas enrichment and preservation include sustained gas supply and reservoirs far away from the ancient/present denudation areas and oil-gas escape areas in large faults. At present, the shale gas resources in Wufeng-Longmaxi formations are 33 19×10 ¹²m ³ with a proved rate of 9.4%, showing great exploration potential. (3) There are rich marine shale gas resources in Sichuan Basin. In addition to Wufeng-Longmaxi formations, there are several sets of marine shale gas reservoirs as reserves in the horizons shallower than 4 500 m. The Cambrian Qiongzhusi Formation, Permian Wujiaming Formation and Dalong Formation as the strategic breakthrough strata, the favorable shale gas reservoirs mainly lie in Weiyuan-Ziyang area inside and around aulacogen for Qiongzhusi Formation, with the predicted resource potential of 1.40×10 ¹²m ³, and in Jiange-Nanjiang area and Dazhu-Kaijiang area of northern Sichuan Basin, and Lichuan area of southeastern margin of Sichuan Basin for Wujiaping Formation and Dalong Formation, with the predicted resource potential of 0.91×10 ¹² m ³. The Member 1 of Xujiahe Formation as the strategic preparation layer, its favorable shale gas reservoirs mainly lie in Ya'an-Qionglai area, with the predicted resource potential of 0.88×10 ¹² m ³.