Coal-rock gas is a new type of natural gas discovered in recent years, generally buried deeper, and some scholars also call it as deep coalbed methane. The exploration and development of this type of natural gas has made rapid progress, with significantly increasing production. Preliminary research indicates that deep coal-rock gas differs significantly from traditional coalbed methane, shale gas, tight gas, and other gas reservoirs in terms of reservoir characteristics and development methods, and has the potential to become a strategic replacement resource for natural gas in China. Therefore, a new round of national science and technology major projects for oil-gas exploration and development will focus on a series of scientific and technological breakthroughs in deep coal-rock gas. Based on systematical analysis, this paper summarizes the three major scientific challenges and ten key research directions for coal-rock gas exploration and development as follows. (1)The key fundamental geological issues are the accumulation mechanism of coal-rock gas and the construction of coal-measure whole petroleum system. The main research directions include the whole process mechanism of hydrocarbon generation/expulsion and enrichment lower limit of coal rocks, sedimentation and source-reservoir coupling effect of coal measures, multiple reservoir types and structures of coal rocks, and coal-measure whole petroleum system and oil-gas distribution. (2)The key fundamental development issues are the flow mechanism and migration regularities of fluid in coal beds. The main research direction include the occurrence state and migration mechanism of coal-rock gas, controlling factors of fluid co-production in coal reservoirs, and stereo development models of complex fluid systems in multiple (thin)reservoirs. (3)The key fundamental engineering issues are the mechanical characteristics and fracture propagation regularities of coal-rocks. The main research directions include the mechanical characteristics and fracturing mechanism of coal rocks, the interaction mechanism between coal rock and fracturing media, and the instability mechanism of coal reservoirs. The analysis of the above-mentioned major scientific issues and key research directions will provide important support for the efficient exploration and development of deep coal-rock gas, and lay the foundation for improving the geological theory of coal-rock gas with Chinese characteristics and coal measure whole petroleum system.

A great breakthrough has been made in the exploration and development of coalbed methane in Ordos Basin. To futher clarify the geological regularities governing deep coalbed methane enrichment, a systematic analysis was conducted on the hydrocarbon generation mechanism, hydrocarbon accumulation evolution, lithological assemblages, and differential migration-accumulation characteristics of the No.8 coal seam of Carboniferous Benxi Formation. Moreover, the exploration prospects of coalbed methane and favorable areas for next hydrocarbon exploration were also pointed out. The results show as follows. (1)The No.8 coal seam of Benxi Formation is mainly deposited in swamps covered with mixed vegetation and water, and has been stably developed in the basin. It exhibits the hydrocarbon generation and evolution characteristics of "high gas generation intensity and long duration", and lays a material foundation for coalbed methane accumulation. (2)Deep coal reservoirs are characterized with dumbbell-shaped pore size distribution, of which the reservoir spaces mainly consist of organic matter pores such as cell tissue pores and bubble pores, as well as a large number of well-developed cleavage-fracture networks. Micropores account for more than 60 % of the total porosity, and the pore size distribution is obviously affected by reservoir maturity. The study has clarified the four-stage evolution mechanism of coal reservoirs. (3)Deep coal reservoirs have abundant gas, with the average gas content of 21.7 m ³/t, and the free gas content of 24.48 % on average. The adsorbed gas occurs mainly in micropores, and free gas is stored in macropores and fractures. (4)The lithological assemblages control the three-dimensional differential migration and accumulation of coalbed methane. The coal-mudstone assemblage and the coal-limestone assemblage show good sealing properties, which are conducive to the in-situ retention and enrichment of coalbed methane. On this basis, the paper establishes a deep coalbed methane accumulation mode of "continuous hydrocarbon generation, source-reservoir-accumulation integration, three-dimensional hydrocarbon expulsion, and differential enrichment". Based on the geological characteristics of deep coalbed methane, three favorable exploration areas have been determined in the study area. Additionally, the paper establishes a comprehensive theoretical and technical system encompassing gas enrichment geological theory, geophysical exploration and prediction, full through-type fracture network fracturing technology, and efficient development of geological engineering, which lays a solid foundation for the effective utilization of deep coalbed methane. This understanding is expected to provide significant references for pioneering large-scale exploration and development of deep coalbed methane, promoting exploration breakthroughs in coal reservoirs of other basins in China, and leading the rapid development of the deep coalbed methane industry.

The research of Whole Petroleum System (WPS) theory, emerging as a frontier field in the petroleum and natural gas geology at present, has attracted extensive attention from both the petroleum industry and academic community since its proposal. Expanding beyond the traditional concepts of petroleum systems, the research of WPS theory involves the geological regularities and resource development of unconventional oil and gas, representing an evolution and development of the petroleum system theory. This paper elucidates the fundamental principles of WPS theory, and summarizes the research progress during its development, including:(1) research advances and exploration practices of the Permian WPS in Junggar Basin; (2) the differential enrichment in the sequential distribution pattern of conventional and unconventional oil and gas, as well as the hydrocarbon accumulation and enrichment mechanism controlled by "source-reservoir coupling"; (3) hydrocarbon migration models in WPS; (4) analysis of WPS in sedimentary basins with the development of multiple sets of source rocks; (5) research and development of the new-generation basin modeling technology and genesis-based hydrocarbon resource appraisal methods on the basis of WPS theory.

Intelligent drill bits are one of the core components of future intelligent drilling systems. By integrating sensors capable of stable performance under high-temperature and high-pressure conditions, adaptive control algorithms, and optimized drill bit structures, these advanced drill bits enable real-time downhole condition monitoring, dynamic adjustment, and precise execution, thereby improving drilling efficiency. As oil and gas exploration expands to ultra-deep formations and complex, unconventional reservoirs, drill bits face increasingly harsh geological conditions. Traditional drill bits, under high-temperature and high-pressure environments and complex geological settings, suffer from challenges such as rapid wear, short service life, and high drilling costs that urgently demand the development and application of high-performance drilling technology. This further highlights the importance of intelligent drill bits as a pivotal future direction for improving drilling speed and efficiency. By systematically summarizing and analyzing the current research, core technologies, and product advancements in intelligent drill bits, such as multi-parameter sensing technology capable of withstanding extreme downhole environments, machine learning- and deep learning-based adaptive control algorithms, and progress in drill bit structure and control mechanisms, this work reveals the potential of intelligent drill bits in modern drilling operations. Typical case studies from both domestic and international projects demonstrate the advantages of intelligent drill bits in enhancing rate of penetration, extending bit life, and reducing unplanned downtime. Looking ahead, research on intelligent drill bits will move toward higher autonomy, broader adaptability, and deeper integration with digital platforms. They are poised to play an even greater role within the intelligent drilling technology framework.

The ultra-deep Mesozoic volcanic trap group in the surrounding area of Bozhong sag has great exploration potential for forming large and medium-scale volcanic oi-gas reservoirs. In recent years, both Well BZ8-3S-A and Well BZ8-3S-B deployed in the Bozhong8-3 South structure in the southwest low uplift zone of the sag have achieved high-yield oil-gas flow from volcanic reservoirs. This breakthrough marks the new exploration progress of large and medium-scale volcanic hydrocarbon reservoirs in the deep subsags of Bohai Sea. Based on the analysis of the core, thin section and source rock, in combination with well logging and seismic interpretation data, the paper systematically investigates the formation conditions and accumulation characteristics of large-scale volcanic oil-gas reservoirs in Bozhong sag, and also explores the seismic prediction methods of favorable volcanic reservoirs. The Mesozoic Yixian Formation volcanic rocks in Bohai Sea consist of 4 eruption cycles, and the large-scale acidic volcanic reservoir represented by the Bozhong8-3 South structure are mainly constructed by the third eruption cycle. The Bozhong8-3 South structure exhibits favorable hydrocarbon accumulation conditions as below. (1) The Mesozoic volcanic buried-hill reservoir is adjacent to three sets of high-quality Paleogene source rocks in the Member 1 and 3 of Shahejie Formation and Dongying Formation, which provide superior oil-gas supply conditions. (2) Four laterally stacked large acid volcanic edifices suffer from the strong superimposed transformation of weathering, tectonic activities and fluid flows, forming large-scale volcanic rock reservoirs. (3) There is a multi-dimensional hydrocarbon charging mode based on the combination of the lateral direct source-reservoir contact and unconformity migration, and the source rock formations with an overpressure coefficient of 1.5 to 1.8 can not only provide sufficient hydrocarbon migration driving force, but also enhance the sealing capacity of the mudstone overlying volcanic rocks. (4) The Bozhong8-3 South structure develops massive condensate-rich gas reservoirs with large gas-bearing formation thickness, high gas column height, high temperature and high pressure, late to ultra-late accumulation. Through the analysis of the seismic response characteristics of the drilled wells, the maximum amplitude and arc length attributes were optimized to predict the distribution patterns of weathering crust. Additionally, the multi-attribute cluster analysis was applied to predict reservoir development zones. On this basis, a seismic prediction technology was established for large-scale favorable volcanic reservoirs in the Bozhong8-3 South structure. The research methods and understandings are of important significance for guiding the exploration of ultra-deep volcanic reservoirs in Bohai Sea.

The cumulative hydrocarbon production in the oilfields in the eastern South China Sea has achieved nearly 400 million tons of oil equivalent over the years, making outstanding contributions to China’s energy security and economic construction. However, after more than 40 years of exploration and development, the remaining potential of conventional oil and gas is exhausted, and the deep oil and gas have become strategic replacements for guaranteeing sustainable reserves and production. This study focuses on the key issues encountered by oil and gas exploration in deep formations, such as basin formation, hydrocarbon generation, reservoir formation, and hydrocarbon accumulation. Using three-dimensional seismic, drilling data, and core analysis results, the hydrocarbon accumulation conditions in deep to ultra-deep reservoirs were systematically investigated from multiple perspectives, including the formation mechanism of hydrocarbon-rich sags/subsags, development mechanism of effective reservoirs, and hydrocarbon enrichment patterns. This provides new geological insights as below. (1)The composite continental-margin magmatic arcs control the formation and evolution of large lake basins. (2)Potassium-rich fluid transformation controls the development of effective reservoirs. (3)Seal and migration mechanism of transtensional fault systems controls hydrocarbon migration, accumulation, and enrichment. These findings guided the integrated evaluation and cluster drilling of the Huizhou 19-6 structure, leading to the discovery of billion-ton-scale oilfield in deep to ultra-deep clastic formations in China’s offshore area. The discovery of the Huizhou 19-6 structural oilfield further reveals that deep oil and gas of the Pearl River Mouth Basin are important replacements for the future growth of hydrocarbon reserves and production, demonstrating the huge exploration potential of deep to ultra-deep reservoirs in the offshore high-geothermal, highly tectonically active composite continental-margin basins, which provides important reference and inspiration for the exploration of petroliferous basins with similar structural settings.

Xihu sag in the East China Sea Basin is the largest hydrocarbon-bearing sag in China's offshore area, and is also one of the main battlefields for offshore natural gas exploration and development in China. In the past five years, based on the "positive rhythm channel sand dessert" seismic prediction while drilling monitoring technology, "permeability classification-dessert thickness ratio" high-efficiency well type design and productivity evaluation technology, and oil-based mud long open hole productivity release technology, the geological-engineering integration technology system innovation and effective practice have been carried out. Xihu sag has obtained commercial gas flow in many low-ultra-low permeability fields, showing good potential for low-ultra-low permeability natural gas storage and production. Based on the analysis of core, mud logging, logging, seismic and other geological data and the exploration and development practice of typical gas reservoirs, the accumulation characteristics and resource potential of low permeability and ultra-low permeability natural gas reservoirs in Xihu sag are systematically analyzed. The Eocene Pinghu Formation in the Xihu sag develops two types of source rocks:the delta-tidal flat facies coal measure source rock in the slope zone and the tidal flat-lagoon facies sapropelic humic source rock in the sag area, showing a full-sag distribution pattern. The tidal flat sedimentary system of Pinghu Formation has the near-source enrichment conditions of natural gas with "self-generation, self-storage and self-cover", and the natural gas accumulation conditions are superior. Controlled by the structural pattern of "east-west zoning and north-south block", three new models of differential enrichment of natural gas are developed in the central anticline belt of Xihu sag. The lithologic oil and gas reservoirs of Pinghu Formation in the western slope zone have the oil and gas distribution law of "vertical superposition and horizontal connection". The large-scale structural traps in the north of the central anticline belt, the lithologic traps in the wing of the central and southern anticlines, the deep Pinghu Formation in the south and the near-sag areas in the western slope belt are the key exploration directions for the low-permeability and ultra-low-permeability gas reservoirs in Xihu sag. The natural gas resources exceed 500 billion cubic meters.

In the study of enhanced oil recovery (EOR)in reservoirs, conventional simulation methods typically use core flooding techniques as evaluation tools. However, the inability to directly observe the internal flow process within the core makes it difficult to clarify the microscopic oil displacement characteristics at the pore scale, thereby limiting the in-depth investigation of the mechanism of efficient reservoir exploitation. This paper reviews the current flow visualization technologies for investigating microscopic mechanisms in reservoirs, and elaborates on the fabrication methods and application scopes of various models. The quartz-glass microscopic flow model, which enables micron-scale pore simulation and possesses the advantages of high-temperature and high-pressure resistance, has become the preferred method for visualizing microscopic flow in reservoirs. Additionally, the paper summarizes the applications of the model in various types of tertiary oil recovery technologies, such as gas flooding and chemical flooding tertiary oil recovery. To simulate real reservoir environments and meet the demands for studying the micro- and nano-scale flow mechanisms of oil reservoirs, future improvements in the quartz-glass microscopic flow model are proposed from three perspectives:external coordination and configuration, in-situ pore wall property restoration (including clay minerals and wettability), and dual upgrades in terms of scale and dimension.

This study aims to provide theoretical guidance for the exploration direction in Baoding sag and Raoyang sag of Jizhong depression, Bohai Bay Basin. Specifically, the overall oil and gas resource types and migration distribution characteristics of both sags were analyzed based on the Whole Petroleum System theory in combination with regional hydrocarbon geological features. Through hydrocarbon generation-expulsion modelling of source rocks in different strata, the resource potential of various hydrocarbons was calculated, and the models of hydrocarbon accumulation in different formations were established. The results show as follows. (1)The source rocks of Member 1 of Shahejie Formation in Baoding sag are characterized by early hydrocarbon generation and expulsion, reaching the hydrocarbon generation and expulsion thresholds at vitrinite reflectance values of 0.35% and 0.45%, respectively. (2)The Whole Petroleum System in Baoding-Raoyang sags have their own vertical boundaries and converge near the Gaoyang low-uplift, which jointly contribute to the development of oil and gas reservoirs near Gaoyang fault. (3)The total hydrocarbon yield from different source rocks of Baoding-Raoyang sags is 73.94×10 ⁸t, with the retained hydrocarbons of 48.67×10 ⁸t in shale, indicating huge exploration potential. (4)Comprehensively considering the Whole Petroleum System, the accumulation modes are divided as the shallow hydrocarbon accumulation model characterized by dual source hydrocarbon supply, fault adjustment, and shallow enrichment in Dongying Formation in Baoding sag, the middle and deep hydrocarbon enrichment mode characterized by migration along slopes and faults, distribution around subsags, and local enrichment in buried hills in Raoyang sag, and the oil and gas enrichment model characterized by near-source migration and intra-source accumulation in both tight and shale reservoirs.

China has achieved major breakthroughs in the exploration of deep coal-rock gas, marking a strategic shift from traditional shallow coalbed methane to deep coal-rock gas. As a high-quality source rock, coal-rock is characterized by high organic matter abundance, continuous gas generation throughout its entire evolution process, and strong storage capacity, which is conducive to the formation of coal-rock gas reservoir where adsorbed and free gases coexist. Based on the new theory of "whole petroleum system of coal measures", this paper reveals the accumulation mechanism and resource potential of coal-rock gas. The preliminary evaluations indicate that the deep coal-rock gas resources with a burial depth greater than 1 500 meters exceed 100×10 ¹²m ³ in China, approximately twice that of conventional natural gas resources, providing a resource foundation for the formation of super-large gas fields. In Daji block of Ordos Basin, large-scale development has been achieved through the application of horizontal well and volumetric fracturing technologies, with an average daily production of 12×10 ⁴m ³ per well and cumulative proven reserves of 1 452×10 ⁸m ³, demonstrating promising development prospects. At present, China has established a series of key technological systems, including experimental testing, optimized drilling and completion, fracturing stimulation, and volume development, which support the efficient extraction of coal-rock gas. However, challenges still exist in coal-rock gas development, such as incomplete theoretical system, unclear sedimentary evolution mechanisms, and insufficient research on accumulation mechanisms. To address these issues, it is suggested to systematically conduct nationwide resource assessments, strengthen exploration in key areas, optimize mining right management, and promote theoretical innovation and demonstration applications. These efforts will provide strategic support for increasing natural gas reserves and production and enhancing China’s energy self-sufficiency capacity.

As the primary oil-generating source rocks in Junggar Basin, Fengcheng Formation source rocks are relatively understudied in terms of their gas generation processes, which impedes the target natural gas exploration in this region. This paper aims to clarify the whole-process gas generation pattern and gas accumulation characteristics of Fengcheng Formation source rocks in western Junggar Basin. Based on hydrocarbon generation simulation experiments in combination with the geochemical characteristics of source rocks, hydrocarbon generation evolution process, and hydrocarbon inclusion observation, a comprehensive analysis was conducted on the product characteristics of Fengcheng Formation source rocks at different maturity stages in the study area. The results show as follows. (1) Based on the variations in gas-oil ratios during hydrocarbon generation from Fengcheng source rocks in western Junggar Basin, the gas generation process can be divided into seven stages:biogenic gas, gas associated with immature/low-mature oil, gas associated with black oil, gas associated with light oil, gas condensate, wet gas, and dry gas. Thus, a whole-process gas generation pattern has been established for Fengcheng Formation source rocks. (2) The paper clarifies the geochemical characteristics of Fengcheng Formation source rocks during the whole-process gas generation. As the maturities of Fengcheng Formation source rocks gradually increases, the carbon isotopes of natural gas and some parameters of light hydrocarbons demonstrate a gradual increasing trend. The carbon isotopes of ethane increase gradually from -38 ‰ to -28 ‰, and the paraffin index gradually increases to above 6. (3) The western Junggar Basin exhibits the high charging intensities for gas associated with light oil, gas condensate, wet gas and dry gas, indicating great potential for both in-source and extra-source natural gas exploration in this area. These research findings can further enrich the geological theory of the Whole Petroleum System in Junggar Basin and promote the efficient exploration of natural gas.

The Whole Petroleum System (WPS) theory has broken through the traditional exploration theoretical framework, with "source-reservoir coupling and orderly accumulation" as its core concept. This theory has proven effective in guiding the coordinated exploration and development of both conventional and unconventional oil and gas resources in northern Xinjiang area of China. In this region, there are three sets of organic-rich source rocks, i.e., the Jurassic, Permian, and Carboniferous-Devonian source rocks, with a total resource of 25 billion tons oil equivalent. Under the guidance of this theory, major breakthroughs have been made in three-dimensional multi-layer exploration across Junggar Basin, Tuha Basin, and Santanghu Basin. Successive reserve discoveries of shale oil in Fengcheng Formation of Mahu sag and tight oil in Jimusaer sag have been achieved over 100 million tons in Junggar Basin. Hydrocarbon exploration in the Shiqiantan sag of Junggar Basin (Carboniferous marine residual strata), Taibei sag of Tuha Basin (Jurassic coal strata), and Tiaohu-Malang sags of Santanghu Basin (Permian strata) has systematically revealed the distribution patterns of various types of oil and gas reservoirs. These findings have enabled the successful, coordinated development of both conventional and unconventional resources. Research has shown that the oil and gas accumulation in northern Xinjiang area exhibits distinct spatial zoning patterns, forming a complete distribution sequence:in-source shale oil-gas in the center, tight oil-gas with variable saturations in the slope zones, and conventional reservoirs along the basin margins. The accumulation mechanism involves multiple dynamic processes, such as buoyancy-driven migration, self-containment effects, and pressure differentials between source and reservoir, demonstrating the dynamic evolution of WPS. Future research should focus on the development of unconventional in-source resources, achieve breakthroughs in key technologies for nano-scale reservoir stimulation, advance the study of dynamic mechanisms governing the whole process from hydrocarbon generation to reservoir formation and accumulation, and establish a comprehensive evaluation technology system for WPS. Exploration practices in northern Xinjiang area have demonstrated both the scientific validity and practical value of the WPS theory, while also offering an innovative paradigm for exploring geologically complex petroliferous basins, which is of strategic significance to national energy security.

The Permian Fengcheng Formation in the Well Pen-1 West sag of Junggar Basin is one of the key strata for natural gas exploration. Previous source-proximal exploration led to occasional modest-scale breakthroughs. In 2023, the Well WT1 deployed in the Mosuwan uplift achieved high-yield industrial gas flow, thus confirming the exploration potential of Fengcheng Formation. This provides a basis for identifying new gas replacement plays, and is of great theoretical and practical significance. To further advance exploration, a study was carried out to investigate the gas accumulation elements and mechanisms using high-precision seismic data and exploration drilling results from multiple wells. The study shows as follows. (1) Glutenite reservoirs are developed in Member 3 of Fengcheng Formation in the source-proximal uplift area of the Well Pen-1 West sag. In the in-source slope area, the Member 2 and Member 1 of Fengcheng Formation are developed. The Member 2 of Fengcheng Formation is primarily composed of mudstone, as the primary hydrocarbon source rock, and the Member 1 of Fengcheng Formation is dominated by lowstand sandstone and dolomitic sandstone. (2) In the in-source slope area of the Well Pen-1 West sag, Fengcheng Formation develops retrogradational braided river delta sedimentary reservoirs, conventional stratigraphic-lithologic gas reservoirs in the source-proximal zone under the background of sedimentary overlap, and continuous tight sandstone gas reservoirs in the source rock. Exploration in the Well Pen-1 West sag has been extended into the in-source slope area, identifying a favorable exploration zone of exceeding 3 000 km ². With the natural gas resource potential exceeding 400 billion cubic meters, this area is expected to become one of the primary targets for natural gas exploration and development in Junggar Basin.

The design of a tension mooring system plays a key role in the overall layout of deepwater semi-submersible production platforms. To explore the influence of the connection point position between the mooring line and hull, anchor position, and mooring line configuration on the maximum mooring line tension and platform maximum displacement, a finite element model of the tensioned mooring system for semi-submersible platform was established using numerical analysis software in this research. An automatic simulation program was developed through data interface integration to generate a sample set. Subsequently, the backpropagation neural network combined with genetic algorithm was employed to optimize design parameters of the mooring system, thus deriving the optimal mooring system configuration. The results show that compared with the pre-optimization data, the maximum mooring line tension is reduced by 10.04 %, and the platform maximum displacement is reduced by 25.29 % . The prediction error of the algorithm is controlled within 10 % . The combination of numerical simulation with the neural network-genetic algorithm provides engineering guidance for the mooring system design of deep-water semi-submersible production platform.

The proposal of the Whole Petroleum System (WPS) theory has significantly enhanced the understanding of hydrocarbon accumulation theories, thus facilitating a series of major exploration breakthroughs in multiple basins in China. This study focuses on the hydrocarbon exploration and development in Junggar Basin, with an aim to further develop and refine the WPS theory and guide domestic and international oil and gas exploration and development. Initially, through analysis of new challenges posed by WPS to seismic exploration technology, the paper elaborates in detail on the research progress of seismic exploration technology and predicts its development trends. The research results show as follows. (1) The WPS theory poses three challenges to seismic exploration technology, i.e., achieving ultra-high shot and trace density acquisition and massive data processing, addressing the issue of coupling diverse target objects and multi-scale data, and enhancing seismic resolution and prediction accuracy. (2) During hydrocarbon exploration in Junggar Basin, four key technological breakthroughs have been achieved. Specifically, the seismic data acquisition technology has undergone a leap from conventional three-dimensional surveys to wide-band, wide-azimuth, and high-density nodal acquisition with high efficiency, the seismic data processing technology has further improved high-resolution, high-fidelity, and high-precision processing techniques, a basin-level high-precision seismic data platform has been established based on new seismic acquisition and processing technologies, and the progress in interpretation technologies such as discrete element numerical simulation, intelligent seismic facies characterization, multi-attribute interpretation of strike-slip faults, geological and engineering "sweet spot" reservoir prediction, and seismic-geological-engineering integration has provided new methods for studying the "tectonic system, sedimentary system, hydrocarbon transport system, accumulation system, and engineering support system" in WPS. (3) Three development trends in seismic technology for WPS exploration have been identified, i.e., seismic acquisition technology centered on ultra-high density, multi-wave and multi-component, seismic data processing technology promoted by the coordinated development of intelligent, high-performance computing and high-resolution imaging, and seismic interpretation technology with intelligent, quantitative, and dynamic characteristics.

The Junlian coalbed methane field in southern Sichuan Basin, as a mountainous coalbed methane field that has achieved large-scale commercial exploitation within the shallow transformation area in southern China, has maintained a stable coalbed methane output of over 1×10 ⁸m ³/a for eight consecutive years. The Junlian coalbed methane has the characteristics of mountainous coalbed methane, which are "located in a complex mountainous area, developed in thin coal seams under the control of waves and tidal flats, deeply buried in the early stage with high-rank coal for hydrocarbon generation, underwent shallow transformation for reservoir adjustment and occurrence in the late stage, had low permeability of coal rock, and contained adsorption gas at normal pressure". Compared with other coalbed methane fields at home and abroad, the efficient exploration and beneficial development of the Junlian coalbed methane fields are confronted with "two deficiencies" (no experience in the exploration and development of high-rank coalbed methane in thin interbedded coal seams on plateau and mountainous areas, and no mature drilling and pressure production technology for karst landforms to draw upon)and "four difficulties" (difficulty in the deployment of sweet spot selection in Wumeng Mountain area, difficulty in implementing drilling and pressure production technology under the karst geological conditions on the surface of karst landforms, difficulty in intelligent and precise drainage and production for low-yield water pressure reduction, and difficulty in gathering and transporting mountainous coalbed methane with low production, low pressure and low cost). Based on the characteristics and technical difficulties of shallow transformation of thin interbedded coal seams faced by the Junlian coalbed methane field, through systematic research on the accumulation laws and key technologies of coalbed methane, it has been clarified that the coalbed methane reservoir of the Upper Permian Leping Formation in southern Sichuan Basin has the characteristics of "shallow transformation, over-maturity with high-rank coal, thin layer, low permeability, low pressure and low water content". The occurrence and enrichment mechanism of shallow and thin interbedded coalbed methane reservoirs in mountainous areas, namely "tidal flat and marsh controlling coal seams, early deep burial-thermal evolution controlling hydrocarbon generation, late and shallow adjustment controlling gas reservoirs, and current retention-confined water area controlling sweet spot enrichment", has been revealed. A sweet spot model of "wide and gentle syncline rich gas" in residual structural depression under the basin-mountain coupling effect of shallow transformation has been established. The technical difficulties in the exploration and development of mountainous coalbed methane under the karst geological conditions of the exposed carbonates have been overcome. A series of continuous and effective exploitation technologies for shallow low-pressure coalbed methane in complex mountainous areas have been established, featuring "low cost, practicality and high efficiency", including integrated sweet spot evaluation and deployment design, factory rapid drilling and fracturing, intelligent precise pressure control drainage and production, as well as integrated production and sales of surface gathering and transportation. The successful development of the Junlian coalbed methane field marks a crucial step forward for the coalbed methane industry in southern China. Its exploration geological theory and key development technologies have promoted the formation and application of the "Junlian Model", providing an important demonstration for the efficient utilization and industrial chain development of the same type of shallow, thin-interlayer and high-rank coalbed methane resources in southern China and other regions.

The current study mainly focus on the application of intelligent methods to improve the efficiency and reliability of technologies for optimizing parameters and identifying operational states in drilling and production processes, which exhibit great potential for future development. However, in the development of intelligent engineering technologies for oil and gas drilling and production, the smart optimization algorithms and predictive models still face the challenges including poor timeliness, weak robustness, and limited reliability. This hinder the practical application of artificial intelligence (AI)methods in oil and gas engineering. The paper provides an overview of the development status of AI methods and intelligent technologies for oil and gas drilling and production in China and abroad, involving engineering design and parameter optimization for well drilling and completion, evaluation of hydraulic fracturing performance and optimization of process parameters, diagnosis of artificial lift system failures, and prediction of reservoir properties and productivity. It further summarizes and analyzes the major challenges including a heavy reliance on labeled data for model training, poor model interpretability and weak performance in small-sample learning, inadquate validation of engineering applicability and reliability, poor timeliness of AI methods in performing optimization tasks, and limited flexibility in multi-objective optimization decision-making methods. Based on aforementioned challenges and the current research state of drilling and production technologies in China’s petroleum industry, this paper proposes several suggestions for the development of AI methods in oil and gas drilling and production as below:(1)establishing standardized, shared industry databases to support intelligent model comparison and validation; (2)enhancing research on learning paradigms to reduce the dependency on labelled data; (3)strengthening research on intelligent optimization methods to improve decision-making efficiency and timeliness; (4)focusing on studying physics-contrained data-driven models to improve the reliability of hybrid physics-data driven models; (5)advancing research on sample balancing and augmentation techniques to improve minority class recognition and model stability; (6)making efferts to develop multimodal data fusion and processing methods to boost the prediction accuracy and engineering robustness of intelligent models; (7)leveraging the advantages of general and industry-specific large models to enhance interpretability and accuracy of intelligent optimization decision-making for drill and production operations under multiple scenarios.

The Xujiahe Formation in Sichuan Basin possesses abundant tight sandstone gas resources, which has long been a key target for increasing reserve and production. However, the hydrocarbon exploration and development efficiency has been low due to the factors including tight reservoir, complex gas-water interactions, unclear accumulation mode, great difficulties in reservoir and fracture prediction, and poor applicability of reservoir fracturing stimulation technologies. In recent years, efforts have been made to achieve a breakthrough in integration project of geology, geophysical prospecting and engineering, by which Hexingchang gas field, a deep tight sandstone gas field in the Member 2 of Xujiahe Formation, has been successfully established. This achievement has contributed to the newly-proven geological natural gas reserves of 1 330.12×10 ⁸m ³, and the annual natural gas production of more than 10×10 ⁸m ³. The results show as follows. (1) There are several sets of high-quality source rocks such as Xiaotangzi Formation and Member 2 of Xujiahe Formation in Hexingchang gas field, featuring vertically superimposed development and extensive lateral distribution, which in combination with thick-bedded high-energy channel tight sandstone reservoirs form a good source-reservoir assemblage. (2) Multi-type large-scale transportation systems provide large storage space and highly efficient migration pathway for natural gas. (3) The Hexingchang gas field demonstrates the hydrocarbon accumulation and enrichment mode featuring multi-stage oil-gas charging, massive gas-bearing reservoirs, and efficient enrichment through large-scale migration system. The coupling between hydrocarbon generation and reservoir formation are decisive factors for the dynamic accumulation process characterized with early-stage large-scale charging of medium-low maturity hydrocarbons, mid-stage low efficient diffusive charging of high-maturity natural gas, and late-stage efficient migration and accumulation through migration systems. The spatiotemporal coupling relationships among source rocks, reservoirs, and migration systems play a key role in controlling the large-scale hydrocarbon accumulation and enrichment. Meanwhile, on the basis of the pre-stack stochastic inversion reservoir prediction technology via frequency-division reconstruction and the fine fracture characterization technology via multi-attribute fusion, a suit of differentiated development technologies tailored to diverse-scale migration systems and volume fracturing technologies of complex fracture networks have been established, which help achieve the efficient exploration and development of deep ultra-low permeability tight sandstone gas reservoirs in Xujiahe Formation of the western depression of Sichuan Basin. Moreover, these integrated technologies have promoted technological innovation in related fields, providing experience and reference for the exploration and development of similar gas reservoirs at home and abroad.

Mahu sag in Junggar Basin develops a typical Whole Petroleum System (WPS), which exhibits the ordered distribution of conventional and unconventional hydrocarbon reservoirs. This has important implications for advancing the development of petroleum geology theories. Through systematic analysis of the petroleum accumulation elements in WPS, the paper summarizes the hydrocarbon enrichment patterns in the study area. Specifically, the WPS of Mahu sag is characterized by distinctive alkaline lacustrine source rocks with sustained hydrocarbon generation throughout the thermal evolution, diverse reservoir types developed across all grain-size sequence (from sandy conglomerates to dolomitic siltstones and argillaceous mudstones), three-dimensional distribution of hydrocarbon transport system enabling efficient oil and gas migration, and a diverse range of orderly accumulated hydrocarbon reservoirs. The source-reservoir configuration, along with their spatiotemporal coupling with hydrocarbon accumulation, forms the core of WPS. Since the end of the Permian period, the Fengcheng Formation source rocks have undergone continuous burial and multi-phase hydrocarbon generation and expulsion, thereby providing a sustained resource basis for hydrocarbon accumulation; the development of sandy conglomerate, dolomitic siltstone and argillaceous shale reservoirs across all grain-size sequence controls the ordered distribution of both conventional and unconventional hydrocarbon reservoirs. The WPS of Mahu sag undergoes sustained and temporally sequenced hydrocarbon charging, demonstrated by early-stage accumulation in conventional far-source reservoirs while later-stage accumulation in unconventional intra-source shale oil and gas reservoirs. The study reveals the whole-process accumulation mechanism of WPS and highlights unconventional intra-source resources as a key frontier for deep exploration. These findings are valuable for refining WPS theory and guiding future exploration practice.

In the eastern slope area of Shijiutuo uplift of Bohai Sea, the main oil-bearing strata is the Lower Member of Neogene Minghuazhen Formation. Conventionally, it is believed that the hydrocarbons only pass through the transport layer in Neogene Guantao Formation, without any retentions. Moreover, the Lower Member of Minghuazhen Formation is dominated by small-scale river channel deposits, leading to poor exploration efficiency. Based on the drilling, seismic, and geochemical data, combined with physical simulation experiments of hydrocarbon migration, studies were carried out on the hydrocarbon enrichment patterns in the Lower Member of Minghuazhen Formation in the slope area of the uplift. The results show as follows. (1)The eastern Shijiutuo uplift is adjacent to Bozhong depression and Qinnan depression, of which the source rocks are of good organic matter type and high maturity. Shahejie Formation in Bozhong depression is the main hydrocarbon source rock strata. (2)The activity rate of Shijiutuo No.1 fault was relatively large in the later stage, and the Paleogene fan bodies were generally developed on the downthrown side of faults, and playing the role of hydrocarbon transfer station. The assemblage of faults and fans bodies promotes the large-scale hydrocarbon vertical migration. (3)The transport layer of Neogene Guantao Formation in the eastern Shijiutuo uplift is located on a wide and gentle slope, with the slope angle generally less than 1.0°, providing favorable conditions for the retention of crude oil in transport layer. (4)Under the control of the pre-existing No.1 and No. 2 strike-slip faults, the strike-slip adjusted faults were formed in the shallow layers of Shijiutou uplift in the later period. By contrast, No. 2 strike-slip fault has relatively stronger activity, and the corresponding strike-slip adjusted faults have longer extension distances thus facilitating the vertical migration of crude oil from Guantao Formation to the Lower Member of Minghuazhen Formation. (5)Under the background of the arid climate in the Neogene, the supply capacity of the sediment source was enhanced, and the river channel was prone to frequently burst, resulting in the formation of large-scale and connected sand bodies dominated by river channel deposits. Guided by the above understandings, the paper establishes a hydrocarbon enrichment mode of "oil transported through Guantao Formation and retained in the gentle slope, oil migration controlled by strike-slip faults, and oil trapped in the Lower Member of Minghuazhen Formation due to channel avulsion" in the slope area of Shijiutuo uplift. The Qinhuangdao27-3 oilfield was successfully discovered in the Lower Member of Minghuazhen Formation. The key exploration technology for discriminating the connectivity of the large-scale connected sand bodies in the Neogene provides important technical support for the efficient evaluation of Qinhuangdao27-3 oilfield. The new geological understandings and key technologies formed during oilfield exploration offer a favorable reference for the exploitation of extra-source strata in the slope of Bohai Bay Basin.