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.

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.

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.

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.

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.

In 2024, according to the exploration idea of "fracture-cavity gas reservoirs formed after fracture reconstruction of carbonate rock", three exploration wells were deployed in the Ordovician subsalt area of Ordos Basin to test gas and obtain high-yield industrial gas flow, revealing good exploration potential for the subsalt fracture-cavity gas reservoirs. However, the high-yield and enrichment regularity and comprehensive prediction model of fracture-cavity gas reservoirs are still unclear, making it difficult to determine favorable zones and achieve drilling targets. Therefore, based on cores, thin sections, seismic data, logging data, and production performances, this paper investigates the basic geological conditions and high-yield and enrichment mechanism of the Ordovician subsalt fracture-cavity gas reservoir in Ordos Basin. The results show as follows. (1)The subsalt fracture-cavity gas reservoirs have dual source hydrocarbon supply conditions of the Upper Paleozoic coal measures and Lower Paleozoic marine source rocks, of which the latter are the main source rocks, with the maximum hydrocarbon generation intensity of 1.2×10 ⁸m ³/km ² and sufficient hydrocarbon supply capacity. (2)The reservoir spaces of the subsalt fracture-cavity units are mainly composed of fractures and dissolution pores developed along the fracture zone, mixed with a small amount of matrix intergranular pores. The average porosity can reach more than 10 %, and the average permeability can reach up to 10 mD, demonstrating good reservoir performance. (3)The subsalt faults and associated fracture systems can not only improve the physical properties of dolomite reservoirs and form fracture-cavities with good reservoir performance, but also communicate source rocks with reservoirs, thus providing effective channels for oil and gas to accumulate in fracture-cavity reservoirs. (4)The thick layer of gypsum-salt rock developed in the 6th submember of Member 5 of Majiagou Formation serves as the regional cap rock for the fracture-cavity gas reservoir. The gypsum-salt rock developed in the 10th submember of Member 5 of Majiagou Formation, as well as the Member 3 of Majiagou Formation, serves as the cap rock overlying on the gas reservoir. Moreover, the tight carbonate rocks around the fracture-cavities form lateral sealing, and those good preservation conditions are conducive to natural gas enrichment and formation of fracture-cavity gas reservoirs. Through comprehensive evaluation, it has been preliminarily determined that the favorable exploration area for the Ordovician subsalt fracture-cavity gas reservoirs is about 2.5×10 ⁴km ², and the estimated natural gas reserves can reach 5000×10 ⁸m ³, indicating great exploration potential. It is an important direction and real target for exploration of the Ordovician subsalt natural gas.

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.

This paper presents the current development state of shale oil and gas in home and abroad and systematically reviews the new technologies, equipment, materials, and software in the fields of shale oil and gas drilling, completion, and fracturing engineering, which are developed by China National Petroleum Corporation(CNPC) based on adhering to a problem-oriented approach tailored to the geological characteristics of China’s continental shale oil and gas. Through comparing these technologies with the overall shale oil and gas engineering technologies in North American, the paper summarizes the issues and challenges faced by shale oil and gas development in CNPC, and then proposes development recommendations for a "Chinese version" of shale oil and gas engineering technology. These recommendations focus on continuously advancing the research and application of key technologies and equipment, accelerating the research and development of new-generation directional drilling tools, carrying out ahead of time the research and development of in-situ conversion technologies for medium- to low-maturity shale oil, and vigorously promoting digital transformation and intelligent development. The goal is to enhance the support provided by engineering technology for shale oil and gas resource development and strengthen its role in ensuring national energy security.

Core analysis can provide support for studying the history of hydrocarbon generation, reservoir formation, and petroleum accumulation, improving oil and gas recovery rates, and searching for large-scale high-quality reserves. With the hydrocarbon exploration and development shifting towards deep and unconventional fields, the reservoirs are highly heterogeneous, and so the previous single-point analysis based on core can no longer meet the needs. It is necessary to comprehensively analyze the multi-scale images and experimental data of cores. Moreover, core analysis has developed from conventional manual description to the current digital core technology, and further towards the intelligent recognition of cores. Firstly, the paper comprehensively summarizes the current research status of core image analysis at home and abroad, and then proposes the definition and connotation of intelligent recognition technology for cores; next, the intelligent recognition of cores has been elaborated based on the case study of how to reconstruct the high-resolution CT images of full-diameter pore structure using micro-nano CT images; finally, the application of intelligent recognition technology for cores in reservoir evaluation, fracturing scheme design, and micro-seepage mechanism research is prospected. The proposal of intelligent recognition technology for cores reflects that artificial intelligence technology has begun to upgrade and develop synchronously in the oil and gas field, i.e., from the primary stage of intelligentization and speed and efficiency improvement of single-point business to a higher stage of multi-scale and multi-modal data fusion, application of large model technology in vertical fields, as well as high-quality development.

Tight oil and gas is an important unconventional resource, equivalent to ultra-low permeability and ultra low permeability oil and gas in traditional low-permeability oil and gas. At present, tight gas is the most productive in China, and has achieved an annual gas production of over 600×10 ⁸m ³ in 2023; tight gas are mainly enriched in Ordos Basin and Sichuan Basin. The tight oil production reached 1 193×10 ⁴t in 2023; the main production areas include Member 6 of Yanchang Formation (Chang 6 Member) and Member 8 of Yanchang Formation 8 (Chang 8 Member) in Ordos Basin, the Permian-Triassic tight glutenite reservoir in Mahu sag of Junggar Basin, and Fuyu tight oil reservoir in Songliao Basin. This paper discusses the temporal and spatial distribution characteristics of tight oil and gas resources from the distribution and geological evolution of sedimentary basins in China, tight oil and gas resources are mainly distributed in the Carboniferous-Permian, Triassic-Jurassic-Cretaceous, and Paleogene-Neogene periods. China’s tight oil and gas are mainly accumulated near the source rocks; horizontally, they are primarily distributed within and near source rocks in slope and trough areas; vertically, they are mainly distributed in tight reservoirs above, below, and between source rocks. According to the geological characteristics, reservoir formation mechanisms and conditions, distribution patterns, and main controlling factors of tight oil and gas in China, three accumulation modes of tight sandstone gas are determined as below:continuous tight deep basin gas, quasi continuous tight gas, and tight conventional trap gas; there are three accumulation modes for tight oil:source-reservoir separated and far-source accumulation, source-reservoir connected and near-source accumulation, accumulation in reservoirs alternated with adjacent source rocks. During the 15th Five Year Plan period(2026-2030), in the fields of southern Ordos Basin, central-western Sichuan Basin, deep Songliao Basin, and Ahe Formation in Tarim Basin, the newly proved geological reserves of tight gas are expected to exceed 2×10 ¹²m ³; and in the Chang 6 and Chang 8 members of Yanchang Formation in Ordos Basin, Fuyu oil layer of Quantou Formation in Songliao Basin, Mahu Fengcheng Formation in the western depression of the Junggar Basin and other fields and zones, the proven geological reserves of tight oil is expected to increase by (18-20)×10 ⁸t.

The tight sandstone oil and gas in Tarim Basin is characterized with wide exploration area, large-scale reserves, and low proportion of proved reserves, and also faces the problems of hydrocarbon source distribution, complex reservoir prediction, as well as oil and gas accumulation mode, which restrict the overall profitable exploration and development of tight reservoirs. Based on outcrop profile, experimental analysis, geophysical and well logging data, a detailed analysis is performed on the new fields and resource potential of tight sandstone reservoirs in forelands and basins. The results show that the new fields of tight sandstone oil and gas in Kuqa depression are dominated by the medium to thick gravel sandstones of the Cretaceous Yageliemu Formation and the medium to thick sandstones of the Middle Jurassic Kezilenuer Formation, forming the structural-lithologic reservoirs longitudinally adjacent to high-quality source rocks in the Upper Member of Pusige Formation, and transversely adjacent to structural-lithological hydrocarbon reservoirs in the hydrocarbon generating center of Awati sag. In the north wing of the Kelasu structural belt and the Dongqiu-Dina structural belt in Kuqa depression, the cumulative area of tight oil and gas traps is 1 830 km ² for tight oil and gas, and the predicted natural gas resource is 16 625×10 ⁸m ³. The favorable trap area of tight oil and gas in Kedong structural belt of southwest depression of Tarim Basin is 301 square kilometers, and the natural gas geological resources are estimated to be about 2 930×10 ⁸m ³ and the condensate oil geological resources are about 2×10 ⁸t. The favorable area of tight oil and gas in Kepingtage Formation in the northwest margin of Awati sag is 4 320 km ², the natural gas resources are estimated to be 7 076×10 ⁸m ³, and oil resources are 7 817×10 ⁴t. New fields and resource potential provide a solid foundation for sustained and efficient hydrocarbon exploration.

Sanmenxia Basin is a Mesozoic-Cenozoic fault basin located on the western Henan uplift in the southern margin of the North China block. No petroleum resources and effective source rocks were discovered during previous exploration activities. In recent years, non-profit oil and gas surveys have confirmed the presence of the Paleogene source rocks in the southern margin of the basin and have gained new insights into oil and gas accumulation. To verify the hydrocarbon potential of the basin, Well Yuxiadi 1 was drilled at Hanguguan structural belt. Drilling data of Paleogene Xiao’an Formation reveal that the porosity ranges from 13.43 % to 20.60 %, and the permeability varies from 35.1 mD to 215.5 mD. The drill stem test (DST) results of the lower oil layer of Xiaoan Formation demonstrate a wellhead oil production of 17.52 m ³ under 24-hour intermittent flow conditions (water-free). Through formation testing by layer, combined with mechanical pumping production, the upper, middle, and lower oil layers of Xiaoan Formation have achieved the stable daily oil production of 4.79 m ³, 6.79 m ³, and 15.83 m ³ (water-free), respectively. These results indicate that the Hanguguan structural belt develops the water-free wax-bearing light oil reservoirs characterized with medium-high temperature, medium porosity, medium permeability, medium-shallow depth, and normal pressure. A comprehensive research shows that the oil source of Well Yuxiadi 1 may be derived from the lower Member of Xiaoan Formation and the upper Member of Podi Formation, the mudstone in Liulinhe Formation and its overlying strata serve as regional cap rocks, and normal faults act as the primary hydrocarbon transportation system. Sanmenxia Basin develops four sets of potential source-reservoir-cap assemblages, and it is inferred that its hydrocarbons have the characteristics of "short-distance migration, multiple hydrocarbon accumulation types, and forming reservoir in late stage", and the main accumulation stage is in the Himalayan period. The oil and gas breakthrough in Sanmenxia Basin signifies the emergence of a new petroliferous basin, which is expected to re-attract attention from the industry on medium- to small-sized basins, such as Southern North China Basin and Weihe Basin. This is of certain reference value and guiding significance to the exploration of oil and gas resources in these basins.

With the continuous growth in global energy demand, the exploration and development of tight oil and gas resources, as a crucial component of unconventional oil and gas, is increasingly gaining attention. Tight reservoirs have the characteristics of low permeability and complex pore structures, posing high demands on drilling fluid technology. This paper reviews the challenges and current research status of drilling fluid technology for tight oil and gas, elaborats on the action mechanisms and performance characteristics of water-based drilling fluids, oil-based/synthetic-based drilling fluids, and drilling fluid lost circulation prevention and plugging technologies, identifies critical issues in the current drilling fluid technology, and proposes future directions for the technology. For the water-based drilling fluid technology, attention should be paid to improving suspension and carrying capacity, enhancing borehole wall stability, and maintaining rheological stability. For the oil-based/synthetic-based drilling fluid technology, special focus should be paid on improving emulsion stability and wettability, enhancing plugging performance, and addressing issues of the resource utilization or harmless disposal of waste drilling fluids. For the drilling fluid lost circulation prevention and plugging technologies, efforts should be made to develop new materials applicable under various formation pressures and permeability conditions and improve the prediction accuracy of lost circulation location. As one of the key technologies for tight oil and gas exploration and development, the research and advancement of drilling fluid technology is critical for increasing tight oil and gas resources and ensuring national energy security.

As a key supporting technology for building new-type power system and energy system based on new energies, the new energy storage technology has been endowed with a new status in the context of global climate change and carbon neutrality, and is a new driving force for enriching and developing new quality productive forces. The energy storage technology can provide stable support for new energy consumption and large-scale grid connection, acting as the granary and bank of energy, the solutions for new energy issues, and an indispensable member in the new energy system. Developing new energy storage technology is an inevitable path for China to achieve the goals of carbon peak and carbon neutrality (dual carbon) and promote energy revolution. The transition of carbon-based traditional energy to zero-carbon energy under new quality productive forces is an inevitable choice, and the new energies supported by new energy storage technology shoulder the new missions of energy transformation, energy security, and energy independence. New energy storage technology is constantly developing, with a variety of technical routes, each with its own advantages, diverse application scenarios, and multifaceted demands; the technology chains and industry chains are thriving, with rapid growth in installed capacity and increasingly perfect market mechanisms, business models, and standard systems. New energy storage technologies include electrochemical energy storage, mechanical energy storage, electromagnetic energy storage, thermal energy storage, and hydrogen energy storage,etc. There are significant differences in the principles of different energy storage technologies, typical energy storage scenarios, market demands, and construction costs. Currently, lithium-ion battery energy storage occupies an absolute dominant position, and other energy storage technologies are being developed in a diversified manner with gradually increasing applications. Since 2017, new energy storage has maintained a rapid growth trend, with the annual growth rate of more than 50 %. By the end of 2023, the cumulative installed capacity of new energy storage exceeded 35 GW, accounting for 40.6 %. According to the national development guidance and implementation plan for new energy storage, about 177 GW of new energy storage systems will be deployed by 2030, and the average annual growth rate of new energy storage installed capacity will be more than 30 % from 2024 to 2030, and China’s new energy storage technology and system will reach a mature level. New energy storage has flexible and diverse business models and cost recovery mechanisms in terms of the source, grid, and load. It can participate in market transactions as an independent entity, or together with traditional entities in the power trading system. At present, the new energy storage technology faces a shift from the early stage of commercialization to large-scale development, as well as both technical and economic challenges. Firstly, electrochemical energy storage represented by lithium-ion batteries cannot completely avoid the risk of fire and explosion, and its service life, energy density, and cost need to be further optimized. Secondly, operation and maintenance control cannot meet the special production requirements for new energy power generation. Thirdly, the initial investment of new energy storage is high, the profit model is still being explored, and long-term sustainable and healthy development requires further policy support. New energy storage is developing towards technological diversification, full-process safety, and intelligent regulation and control, focusing on solving key issues such as high safety, low cost, long life, high efficiency, large capacity, high integration and intelligence. In the future, the business model of new energy storage will be deeply linked to the process of power market reform, and will gradually develop towards shared energy storage and independent energy storage models. The integrated hybrid energy storage systems formed by the organic combination of multiple types of energy storage technologies can adapt to different application scenarios and demands, and integrate the advantages of various energy storage technologies. Through the introduction of advanced digital scientific and technological methods such as cloud computing, big data, Internet of Things, Mobile Internet, artificial intelligence, blockchain, and edge computing, it facilitates the intelligent integration of new energy storage with the source, grid, and load. It can provide more flexible, efficient, and economical energy storage solutions, improving the system safety of the new power and energy systems. It indicates the development trend of new energy storage technology under the empowerment of new quality productive forces, which is of great significance in promoting the high-quality transformation and development of energies and achieving the goal of double carbon in China.

Underground coal gasification can achieve the clean development and utilization of coal resources, which is in line with the low-carbon development strategy of petroleum enterprises and the national carbon peaking and carbon neutrality goals. The paper sketches the current research status of the theory and technology of underground coal gasification, and it is considered that the theoretical system of underground coal gasification has been fundamentally established, the shallow coal underground gasification technology is relatively mature and has not yet become industrialized. The middle-deep coal underground gasification has been preliminarily validated and become the development tendency of underground coal gasification. However, it still faces key challenges such as complex technology, poor basic studies, and stability control in the gasification process. Since 2019, China National Petroleum Corporation Limited has implemented a number of major science and technology projects, which aims to tackle key technologies for coal underground gasification in the middle and deep strata deeper than 800 m. From both theoretical and technical perspectives, this paper summarizes and introduces important progresses and understandings achieved from the implementation of major projects. In terms of basic theory, the understandings of underground coal gasification kinetics, gasification cavity expansion mechanism and overburden thermal deformation mechanism is deepened based on a breakthrough in experimental technique and systematic experimental and simulated studies, laying a theoretical basis for the engineering and process design of middle-deep coal underground gasification. In terms of process technology, a breakthrough has been made in the key core technologies, including gasification resource evaluation and site selection evaluation, gasifier integrity design and control as well as gasification operation control, thus forming the gasifier construction equipment system and underground gasification borehole operation equipment system. In addition, it is proposed to continue to deepen the basic research on middle-deep coal underground gasification and simultaneously promote field tests, so as to improve technology maturity and process stability, and push forward the industrialization of underground coal gasification.

Following the formation of Eurasian Plate and the closure of Paleo-Asian Ocean, the Kazakhstan Plate (Orocline) was formed in the late Paleozoic. As influenced by the closure of the Junggar-Balkhash Ocean and the hot and arid paleoclimate, a series of residual oceanic and coastal continental margin saline lacustrine basins were formed during the Early to Middle Permian along the oceanic-continental closure zone in Junggar Basin located at the eastern margin of Kazakhstan Plate. The comprehensive analyses of lithology, sedimentary facies, geochemistry, seismic stratigraphy, and seismic lithology show the following. (1) The Lower-Middle Permian Fengcheng Formation, Lucaogou Formation, Hongyanchi Formation and Pingdiquan Formation in Junggar Basin are mainly composed of saline sediments (including residual oceanic and saline lacustrine sediments). Specifically, Fengcheng Formation is mainly distributed in Mahu sag, Penyijingxi sag, Shawan sag and Fukang sag along the closure zone of the western Junggar residual ocean and northern Tianshan residual ocean, Lucaogou Formation and Hongyanchi Formation are mainly distributed in Fukang sag and Bogda Mountain region along the northern Tianshan-Solunke residual ocean, and Pingdiquan Formation is mainly distributed in Wucaiwan sag, Shishugou sag and Shiqiantan sag along the Kalamaili residual ocean. (2) The saline sediments are distributed regularly, and gradually migrated from west to east and from bottom to top from Early to Middle Permian. (3) Fengcheng Formation, Lucaogou Formation and Pingdiquan Formation are the main source rocks of Permian in Junggar Basin, which contain bacteria-rich algal organic matter and are typically characterized by saline lacustrine sediments. (4) The formation and migration of the Early to Middle Permian residual oceans and saline lacustrine basins in Junggar Basin controlled the distribution of sedimentary facies and high-quality source rocks. Petroleum exploration practices reveal that the high-quality saline lacustrine source rocks in Mahu sag in the west and Jimusaer sag in the east of the basin control the formation of hydrocarbon accumulation areas with 1 billion to billions of tons reserves, indicating that there may be great oil-gas resource potential in the distribution centers of saline sedimentary source rocks in Penyijingxi Sag, Shawan sag, the southern margin area of the basin and Fukang sag. Although there is no deep drilling to confirm those at present, their exploration prospects are worth looking forward to.

Faulted basins are important oil and gas production bases in China. With the progress of hydrocarbon exploration, the proportion of the proved conventional oil and gas resources in the shallow and middle layers (depth<3 500 m)has exceeded 60 % , and hydrocarbon resources in tectonic traps of the uplift area are exhausted after years of exploration. There is an increasing difficulty in exploring large-scale oil and gas reservoirs, and the focus is shifted to the exploration of middle and deep layers. Based on the researches of hydrocarbon generation, sedimentation, reservoirs and source-reservoir matching relationship in the Bohai Sea area, the paper systematically summarizes the petroleum geological conditions for tight oil and gas accumulation, which, in combination with the exploration practice of tight oil and gas, an analysis is conducted on the exploration potential of shale oil. The results show that under the control of fault activity, lake level rise and fall, and source supply intensity, there are four types of tight reservoir sedimentation in the middle and deep Paleogene layers, including near-source fan delta in steep slope zone, saline medium braided river delta, sublacustrine fan in slope and depression zone, and carbonate deposition in arid and uncompensated lake basin. When the burial depth exceeds 3 500 m, the reservoir is gradually densified under compaction, and the tight reservoir mainly exhibits the physical characteristics of low and ultra-low porosity and permeability. Deep burial depth, complex composition, and carbonate cementation are the main reasons for the development of tight reservoirs, and dissolution pores and fractures are the main storage spaces. There is relatively large accommodating space in deep depression areas during the pan-lake period, which is conducive to the formation and preservation of organic-rich shale, boasting of superior source rock conditions. The exploration practice of tight oil and gas in the Paleogene reservoirs has confirmed that the Bohai Sea area has the potential for large-scale exploration of tight lithological oil and gas reservoirs, and superior conditions for the development of shale oil as well as enormous resource potential. These unconventional oil and gas resources can provide an important foundation for sustainable exploration and discovery in Bohai oilfield.

In 2023, a major breakthrough of hydrocarbon exploration had been made in Triassic Yanchang Formation of Hongde area, southwestern Ordos Basin, where Hongde oilfield was discovered with 100-million-ton crude oil reserves. To clarify the geological characteristics and accumulation conditions of Yanchang Formation in Hongde area, the factors and patterns of hydrocarbon accumulation were systematically sorted out by integrating core, well logging, 3D seismic and analytical test data. Moreover, the key technologies for hydrocarbon exploration and development were summarized. The research results show that the braided river delta plain subfacies with distributary channel sand bodies are developed in the Member 8 of Yanchang Formation (Chang 8) in Hongde area, where the reservoirs have large thickness and good physical properties, demonstrating excellent conditions for oil accumulation. The source rock in the Member 7 of Yanchang Formation (Chang 7) in Hongde area is characterized with thin layer, and its total organic carbon (TOC) content is 1.16 % on average, thus indicating a low potential for supplying hydrocarbons. The crude oil in Chang 8 of Hongde area is mainly originated from the high-quality source rock of Chang 7 near the center of lake basin in the eastern part of Ordos Basin. The oil migrates laterally through the three-dimensional transport system composed of faults, fractures and high-quality reservoir sandbodies developed in Yanshanian period, and accumulates in the high parts of paleo-structures. Horizontally, the structural and structural-lithologic reservoirs developed in the west of Hongde area are characterized with the hydrocarbon accumulation mode of "lateral migration and accumulation, reservoirs controlled by fault and uplift, and enrichment characteristics controlled by physical properties of reservoirs". In contrast, the large scale of lithologic reservoirs are developed in the east of Hongde area, with the characteristic of being close to source rocks. During the petroleum exploration and development in Hongde area, the study establishes a series of key technologies focusing on 3D seismic processing and interpretation of depth migration, evaluation of reservoir fluid properties based on the integration of well logging and mud logging, and fracturing transformation for fracture controlling and reservoir stimulation. Those technologies have provided strong supports for new oil and gas discoveries. The breakthrough of Hongde oilfield proves that the area far from the oil source of Tianhuan depression still has the potential for large-scale accumulation. The western margin of Ordos Basin is expected to further implement the petroleum geological reserves of more than 2×10 ⁸t, which is a key field for expanding the extra-source oil and gas exploration.

This paper aims to the problems such as the unclear mechanisms behind fracturing fluid imbibition (retention) and its impact on oil recovery and reservoir damage in Fuxing area, as well as the undefined limits for imbibition time and undetermined direction for optimization of the efficient fracturing fluid systems. Through various imbibition experiments, comparative analyses of pore size, permeability, and NMR T ₂ spectra before and after imbibition, and molecular dynamics simulations of interactions between fracturing fluids and shale oil reservoirs, the paper systematically investigates the mechanism of fracturing fluid imbibition in shale oil reservoirs. The results indicate that the porosity, development degree of micropores, total clay mineral content, and mixed-layer illite-smectite (I/S) content can significantly affect the effectiveness of imbibition oil recovery; higher porosity, higher development degree of micropores, and higher contents of clay minerals, quartz, and I/S are more favorable for imbibition oil recovery. Overall, imbibition can enhance pore expansion, permeability, and oil recovery in the Fuxing shale oil reservoir, and these performances can be improved by 70 % or more when using effective fracturing fluids. Fracturing fluids containing nonionic functional groups such as oxyethylene have a significant effect on the overall pore size distribution of the reservoir and can microscopically disperse shale oil molecules and strip them from the organic pore walls. Reservoir damage is minimized by ensuring a imbibition time of 239 h, and the use of fracturing fluids containing nonionic functional groups like oxyethylene can further reduces reservoir damage and enhance imbibition oil recovery.