Oil and gas enterprises face greater risks and challenges in ensuring national energy security associated with the deterioration of domestic oil and gas resources, greater difficulty in increasing reserves and production, continuously higher technical requirements, and constantly increasing development costs. In this context, the development practice of oil and gas fields in China over the past century is systematically reviewed, and the trends and composition of oil and gas reserves and production since the founding of the People’s Republic of China are analyzed in detail, which enable to reclassify the stage of oil and gas field development. Based on resource types of continental, marine, low-permeability, offshore, and shale oil and gas, oil and gas field development theory and technology are deeply summarized. Furthermore, the targeted countermeasures and suggestions are proposed by focusing on the challenges faced by the development of oil and gas industry at present, such as the extremely great difficulty in the innovation of exploration and development theories, demands for further improving the adaptability of unconventional oil and gas exploration and development technologies, high cost of oil and gas development, and the more significant contradiction between resource exploration and development and land lease and environmental protection. Combined with the new development situation, the study proposes that transforming towards intelligence is the fundamental path for the development of oil and gas enterprises, unconventional oil and gas development will occupy a major position in domestic oil and gas development, and green and low-carbon transformation is the inevitable trend for the sustainable development of oil and gas enterprises.

In June 2014, at the sixth meeting of the Central Financial and Economic Leading Group, President Xi Jinping proposed to promote the energy consumption revolution, energy supply revolution, energy technology revolution, energy system revolution and strengthen comprehensive international cooperation, actively promote energy system reform, accelerate the formulation of the overall plan for the reform of power system and oil and gas system, and initiate the work of amending and abolishing laws and regulations in the energy sector, which provided fundamental guidance for deepening reforms, comprehensive green transformation, and high-quality development of oil and gas sector in China. In order to comprehensively grasp the overall requirements of the new energy security strategy in the new era, and the key works and main achievements of the reform of oil and gas system and mechanism, the key laws, policies, standards, and other documents related to the reform of oil and gas system and mechanism since 2014 are systematically summarized, and the main achievements are overviewed qualitatively and quantitatively. The study results show that Chinese government has persisted in promoting the reform of oil and gas system and mechanism for the past decade, and conducted a series of reform measures, including the construction of legal regulations and standard systems in oil and gas sector, transformation of government management functions in the oil and gas industry, guidance and construction of an oil and gas market system, and the promotion of oil and gas pricing mechanism reform, strongly supporting the increase of oil and gas reserves and production, as well as the acceleration of industry development. In the future, associated with the new journey of comprehensively building a socialist modernized country of China, the legal and regulatory system in oil and gas industry should be improved, a capable government and an effective regulatory system should be established, an “X+1+X” oil and gas market pattern should fully be constructed, and an oil and gas pricing mechanism of “controlling the middle and opening up both ends” should be formed, so as to comprehensively ensure the high-quality development of oil and gas industry.

The international oil companies have adhered to a long-term exploration strategy of implementing risk exploration in global frontier domains to achieve substantial investment returns. However, there are considerable differences in their focus and implementation performance of risk exploration among various companies. In order to study the risk exploration strategies, risk exploration preferences, and implementation performance of foreign oil companies, and to guide the overseas petroleum exploration work of Chinese oil companies, oil company annual reports, public information and commercial database are used to analyze risk exploration projects of eight foreign oil companies during 2005–2022. As a result, an evaluation indicator system for project implementation performance has been established, including four primary indicators such as exploration benefits, exploration investment, project scale, and risk control, as well as 19 secondary individual indicators. The benchmarking of individual and comprehensive indicators is conducted, and the effectiveness and experience in risk exploration of the benchmarking companies are analyzed. The study results show that there are significant differences in the individual indicators among oil companies, which are closely related to their exploration strategies and risk exploration preference. ExxonMobil scores the highest in comprehensive evaluation indicators, while BP has relatively low score due to the small number of operator risk projects and a lack of major commercial discoveries. Based on the research findings, insights in five aspects have been concluded for overseas risk exploration of Chinese oil companies, including emphasizing exploration benefits, actively operating as a risk exploration project operator, maintaining certain project scale and investment, appropriately controlling project equity, and formulating risk exploration strategies that align with company characteristics. These suggestions are of important practical significance and have long-term strategic value in guiding the development of overseas petroleum exploration strategies and risk exploration policies for Chinese oil companies.

In recent years, associated with the continuous advancement of mineral resources management reform in China, the original exploration procedures and mineral rights maintenance system of oil companies should be adjusted accordingly. As a result, the integration of exploration, reserve, and mineral rights with the core concept of “integrated research in all fields, integrated deployment in all aspects, and integrated operation in the whole process” has been proposed to realize the transformation from single-item scheme optimization to overall optimization and achieve the results of “1+1+1>3”. The integration of exploration, reserve, and mining rights mainly includes the following aspects: (1) Exploration discovery is the foundation, reserve evaluation is the key task, and the transformation from exploration to production is the ultimate goal. The systematic planning and collaborative promotion of the above three factors should be conducted to ensure the maximum comprehensive benefits of oil companies. (2) A big scientific research system based on the “three-dimensional integration” of technology, economy and policy should be constructed to consolidate the foundation for high-quality oil and gas discovery and high-efficiency transformation from exploration to production through high-quality scientific research; An integrated deployment system based on five key links of “drilling, fracturing, testing, production and sale” should be established, and the quality of deployment should be improved from the source by optimizing top-level design, dynamically optimizing and conducting real-time adjustments; A large operation system of “integration of various types of resources, and unified scheduling and operation” should be constructed, and the organization and operation of production should be optimized to ensure the improvement of speed, quality, and efficiency. (3) In the practice of exploration–reserve–mining rights integration, the “three unified” concept of conceptual identity, management consistency and technical collaboration should be established. From the conceptual perspective, the development consensus of maximum mineral rights interests should be kept in mind; The vertical integration and horizontal connection of management should be implemented, and the control mechanism of key nodes throughout the entire process should be constructed by integrating resources and optimizing procedures, so as to accelerate management reform and efficiency enhancement; The basic technological research should continuously been deepened, and the technological iteration and upgrade should be innovated to achieve the high-quality exploration breakthroughs and reserve increase on a large scale. The integration of exploration, reserve, and mining rights has been practiced in Nanchuan normal-pressure shale gas field in Southeast Sichuan Basin, obtaining remarkable results and developing a number of key technologies for exploration and development of normal-pressure shale gas, which have effectively supported the discovery and construction of Nanchuan normal-pressure shale gas field, with the new addition proven shale gas geological reserves of 1989.64×10⁸ m³, new established mining rights area of 314.5971 km², the cumulative new constructed shale gas production capacity of more than 26×10⁸ m³, and the cumulative shale gas production of more than 65×10⁸ m³ The application enables to build the first large-scale normal-pressure shale gas field in China that has been put into commercial development and achieve the high-efficiency transformation of the value of mineral rights, which has a positive role in unconventional oil and gas exploration and mineral rights management in China.

The Mesoproterozoic Changcheng System was the first set of sedimentary cap rocks in Ordos Basin, with a wide distribution area but low degree of study and exploration. By using field outcrops, drilling results of risk exploration well PT1, and 3D seismic data, a systematic study is conducted on stratigraphic correlation and distribution, sedimentary facies, and source rock characteristics in the Changcheng System. In Ordos Basin, five sets of formations were developed in Changcheng System from bottom to top, including Xiong’er Group, Baicaoping Formation, Beidajian Formation, Cuizhuang Formation, and Luoyukou Formation. The stratigraphic distribution characteristics vary in various rift troughs. In Jinshan rift trough, the five sets of formations were developed completely. In Dingbian rift trough, three sets of formations were developed, including Xiong’er Group, Baicaoping Formation and Beidajian Formation. While only Beidajian Formation was developed in Helan rift trough. The bathyal–shallow marine–coastal–delta sedimentary system was dominant in Changcheng System, intercalated with tidal flat deposits. Effective source rock in Cuizhuang Formation was encountered in Zhongtiaoshan in Xiong’er rift and several exploration wells in the secondary rift troughs, with the highest organic carbon content of 1.52% and average R_o of 2.32%, showing potential of large-scale hydrocarbon generation. The basin thermal evolution simulation shows that Cuizhuang Formation source rock entered the mature stage in the Middle Permian with R_o value of 0.5%, and entered dry gas generation stage in the late stage of the Early Cretaceous with R_o of 2.0%. The comprehensive study shows that the configuration between source rock and reservoir in Changcheng System was good in Ordos Basin, forming self-generation and self-storage type natural gas reservoirs. Furthermore, two exploration targets are optimally selected in Dingbian rift trough and Jinshan rift trough, providing direction for gas exploration “towards source rock” in deep formations in the basin.

The deep–ultra-deep carbonate rock series in Sichuan Basin have an area of about 10×10⁴ km², with superposition and orderly distribution of source rock and reservoir, showing huge exploration potential. After systematically studying the basic petroleum geological conditions of deep–ultra-deep formation in Sichuan Basin, the possible exploration types and their exploration potential are analyzed, and the future exploration orientation is put forward. The study results show that: (1) The “rift–depression” structural cycle controlled the distribution of deep–ultra-deep carbonate reservoirs. Four sets of thick dolomite reservoirs were developed in the region, and their distribution was mainly controlled by sedimentary facies zones, with the most favorable reservoir developed in platform margin at the edge of the rift. (2) The structural pattern of multi-stage alternating uplift and depression controlled the widespread marine source rocks in Sichuan Basin, among which source rocks with the best quality included the Cambrian Maidiping Formation–Qiongzhusi Formation, Silurian Longmaxi Formation, and Permian Longtan Formation. (3) The conventional porosity type carbonate reservoirs were mainly developed in the Sinian–Cambrian and Permian in the northwestern and central–eastern Sichuan Basin, with burial depth of 6000-10000 m. Three types of hydrocarbon accumulation combinations were formed, i.e., lower source rock and upper reservoir, side source rock and side reservoir, and upper source rock and lower reservoir, with superior hydrocarbon accumulation conditions. The key zones for increasing reserves on a large scale include Dengying Formation platform margin and Changxing Formation reef flat in the northwestern margin of Yangtze Craton, and the reef flat in the lower combination in the Sinian and Permian in the eastern Sichuan Basin, with a resource scale of more than one trillion tons. (4) The unconventional marl reservoirs were mainly developed in the first member of Maokou Formation (Mao 1 member) and the second sub-member of the third member of Leikoupo Formation (Lei 32 sub-member), with integrated source rock and reservoir, burial depth of 3000-6000 m, and resources of more than 3×10¹² t, which is expected to be a major replacement field. The favorable area of Mao 1 member is mainly distributed in the eastern–southern Sichuan Basin, while that of Lei 32 sub-member was mainly distributed in the central Sichuan Basin.

Hetao Basin, a proliferous basin showing rapid subsidence and hydrocarbon accumulation in the late stage, has abundant oil and gas resources. In order to identify the potential of ultra-deep oil and gas reservoirs in sub-sag area in Linhe Depression, Well Hetan 101 was deployed and drilled in Guangming structure, and a significant breakthrough was made in Linhe Formation at a depth of greater than 6500 m, with an oil rate of 1285.77 m³/d and a gas rate of 1×10⁴ m³/d. A comprehensive study on hydrocarbon accumulation conditions in the deep to ultra-deep formations in the sub-sag area has been conducted. The study result suggests that the reservoir sand body has the characteristics of high rigid particle content (average of 85%), low geothermal gradient (2.3 ℃ /100m), long-term shallow burial–late deep burial, and low interstitial material content (less than 5%), enabling the preservation of abnormally high-porosity reservoirs at a depth of greater than 6500 m. The pressurization after hydrocarbon generation and under-compaction of mudstone provided driving force for hydrocarbon migration. However, due to the influence of detachment faults, over-pressure only occurred in Guangming structure, with formation pressure coefficient reaching up to 2.0–2.3 in the sub-sag area, forming a self-generation and self-storage type structural oil and gas reservoir with co-occurrence of source rock and reservoir. The vertical fractures in source rock formed by hydrocarbon generation connected multiple sets of source rocks and high-permeability sand bodies, forming ultra-high pressure oil and gas reservoirs both in source rock and reservoir in ultra-deep formations with connected pores and fractures. The successful drilling of Well Hetan 101 once again confirms the broad prospects of petroleum exploration and development in deep and ultra-deep formations in continental fault basins. Guangming structure is expected to become a new large-scale integral and high-efficiency reserve area, demonstrating a new exploration field with high-yield oil and gas in ultra-deep formation, and providing a solid resource guarantee for the construction of a million–ton–level oil field in Hetao Basin.

Ordos Basin is rich in shale oil resource with different level of exploration and cognition basin-wide, and stratigraphic structure of Yanchang formation, forming and controlling factors on enrichment for shale oil need to be deepened.The stratigraphic structure of Yanchang Formation is re-established, and the controlling factors on formation and enrichment are discussed for shale oil of Member Chang7 through the full application of newly acquired high-density and wide-azimuth 3D seismic data, combining drilling logging and analytical data in Ningxian-Zhengning area, southern Yishan Slope belt. The latest comprehensive study show that Member Chang 7 to Chang2 of Yanchang formation has the stratigraphic structure of wedge-shaped development and progradation layer by layer towards the lacustrine center, the provenance of Yanchang formation is mainly from the Qinling Orogenic Belt for Ningxian-Zhengning area, and sedimentary sequence of single-stage wedgeshaped formation is filled with fluvial-delta, semi-deep lake, deep-lake gravity-flow deposits along the sediment-supply direction, which has the characteristics of “same period with different sedimentary facies”. Deposits of sandy debris flow and turbidity flow are developed in Member Chang7 mainly, which belong to low-porosity and ultra-low porosity ultra-low permeability tight reservoir generally with characteristics of rapid lateral change and strong reservoir heterogeneity. The low-permeability, tight oil and shale oil reservoirs are continuously developed encompassing the main source rock of chang 7, resulting in three reservoir combination types including reservoir below source rock, reservoir and source rock co-existing in same layer, reservoir above source rock in Yanchang Formation. intercalated shale oil mainly exists in Chang7, controlled by combination of high-quality source rock, advantageous microfacies, fractures and structure. High-quality source rock controls beneficial distribution range of shale oil,sedimentary facies and fractures control enrichment area.

A shallow–medium coalbed methane (CBM) field has been established in the southern Qinshui Basin with an annual production capacity of 2.6×10⁸ m³. However, the exploration of deep CBM is at a low level, and there is insufficient geological understanding. By using drilling, lab test, and trial production data of exploration wells in the study area, accumulation characteristics of deep CBM have been analyzed from four aspects, i.e., coal reservoir characteristics, thermal evolution and gas-bearing property, preservation conditions, and temperaturepressure characteristics. The study results show that: (1) The No.3 coal seam is consistent, with a total thickness of 4.0-7.3 m, which has the favorable conditions of high vitrinite content, low ash content, and well-developed fissures; (2) R_o of the No.3 coal ranges in 2.41%–3.03%, showing a high-rank coal, which has strong adsorption capacity, with an adsorbed gas content of higher than 20 m³/t; (3) The salinity of the produced water from No.3 coal is greater than 4000 mg/L, showing a NaHCO₃ water type, and it is in a weak radial flow environment. The deep CBM reservoir has the characteristics of slightly low temperature and low pressure, indicating that it has suffered certain damage, which insignificantly affected the adsorbed gas, but was not conducive to the accumulation of free gas. The conclusion suggests that the accumulation conditions for deep CBM in the study area were more favorable than the shallow–medium CBM that has already been appraised and developed in the slope zone. The estimated CBM resources of the deep No.3 coal are 1200×10⁸ m³, indicating good potential for CBM exploration and development.

The deep-ultra deep Permian clastic rock reservoir in the Junggar Basin has been continuously discovered and broken through in recent years, and has become one of the key areas of basin exploration and development, but its overall development characteristics and control factors are still unclear. Coring, logging, thin section analysis and laboratory analysis data of the key wells are used to study and analyze the basic development characteristics and main control factors of its reservoir. This study argued that the deep-ultra deep Permian clastic reservoirs are mainly delta distributary channel conglomerate, followed by sandstone. The gravel is mainly composed of tuff, and the cements are mainly zeolite and calcite, with a well-developed muddy matrix. The storage space is mainly composed of pores and fractures, forming three types of combinations, that are pore, fracture, and pore fracture composite type. The pores are mainly secondary dissolution pores, and three development zones of secondary pores are formed vertically. The cracks are mainly compacted microcracks. The rock composition, diagenesis, and formation overpressure are the main controlling factors for the formation of effective reservoirs, jointly controlling the formation, evolution, and distribution of relatively effective reservoirs in the deep-ultra deep Permian.

In Cangdong Sag in Bohai Bay Basin, the continental shale in the second member of Kongdian Formation (Kong 2 member) has great variation in lithology and high heterogeneity, and shale oil production of horizontal wells is significantly different by applying traditional fracturing technologies. In view of these problems, core section with a length of 500 m in Well G108-8 has finely been described, and well cementing sliding sleeve fracturing technological test in Well GY5-1-9H and comparative fracturing simulation experiments between multicluster hole and single-cluster hole have been conducted, which enable to summarize the adaptability, mechanism, and fracturing construction experience of single-cluster fracturing technology for continental shale oil in fault basins. The study results show that the uniformity of fracture initiation by using well cementing sliding sleeve single-cluster hole fracturing has significantly been improved by 1.65-2.04 times compared to bridge plug multi-cluster hole fracturing, overcoming the failure of fracture opening in some clusters due to competitive fracture initiation, as well as problems of casing deformation caused by fluid fingering advance and frac-hit in some clusters. The process of bridge plug pumping and perforation is eliminated when applying well cementing sliding sleeve single-cluster hole fracturing technology, so the construction process is more continuous. A maximum of 11 stages of fracturing construction have continuously been operated in one day, with a construction pressure reduction of 20%–30%, and the number of fracturing trucks decreased from 20 to 9. In Well GY5-1-9H, this technology has been applied to implement single-cluster hole fracturing for 79 stages and 987 m, with a sliding sleeve spacing (cluster hole spacing) of 12.5 m. After fracturing, the cumulative oil production in the first year was 10128 t, and the predicted ultimate recoverable reserves (EUR) were 3.77×10⁴ t, setting a record for the highest cumulative oil production and single well EUR of the normalized per kilometer section in shale oil horizontal well in China, which was 1.34-3.15 times that of multi-cluster hole fracturing wells in the same oil enrichment zone; It has also been applied in Shulu Sag in Jizhong Depression, and the steady pressure and production have been achieved in shale oil horizontal wells for over 300 days. This technology delivers useful reference for the development of highly homogeneous continental shale oil in China.

The scientific prediction of growth potential of oil and gas reserves is an important prerequisite and foundation for conducting exploration planning and deployment of oil companies. However, all of the commonly used methods have certain deficiencies in predicting oil and gas reserve growth. For example, the prediction methods based on reserve upgrading often have inadequate conditions for application in areas with low level of exploration; The prediction methods based on extrapolation of exploration results lack the concept of time series, so they are difficult to reveal the change rules of oil and gas reserves with time duration. The prediction methods based on life cycles have no connection with exploration workload, so they are difficult to play an effective guiding role in exploration planning and deployment. By properly integrating the petroleum exploration results and time series in this study, a new reserve growth prediction method based on time series of drilling effectiveness has been proposed, and a highly operational modeling and prediction process have been established. In addition, selection strategies for the targeted models in various reserve increase stages have been put forward. The practical application shows that this prediction method is of great significance in revealing oil and gas reserves discovery rules, evaluating the potential of reserve growth, and guiding the exploration planning and deployment in the exploration block.

In the process of thermal recovery of heavy oil in Bohai Oilfield, cyclic steam stimulated wells often face problems of difficult steam injection due to poor reservoir physical properties or blockage of the circumferential borehole. Hydraulic dilation, an innovative technology,effectively solves the problems of short effective period and high operational costs by applying conventional well stimulation methods.However, there are few experimental studies on the characteristics of reservoir hydraulic dilation, especially those considering the initial cyclic steam stimulation stage or the true triaxial stress field in actual formation conditions. Taking Bohai L heavy oilfield as an example, the grain size of core sample has been analyzed and the microscopic physical properties of heavy oil layer before steam injection development have been observed, including the microscopic scanning and energy spectrum analysis. In addition, the mechanical and high-temperature hydraulic dilation features of core samples have been studied in the true triaxial stress conditions. The experimental results indicate that the average grain size of core sample is 225 μm, which shows fine–medium grain size. The microstructure of core sample is relatively loose, and there are asphalt cements among grains. The silicon and carbon contents are the highest in core sample. The shear dilation rapidly occurs in the uniaxial stress of core sample, but the core volume continues to be compressed due to the restriction of horizontal stress in the true triaxial stress conditions, without any dilation, showing low rock strength. In the true triaxial high-temperature hydraulic dilation experiment, the fluid pressure in core sample showed significant fluctuation, which indicated that the internal fractures continued to initiate, develop, and propagate during the hydraulic dilation stage, leading to the volume dilation of core sample, and the core sample still had strong bearing capacity after reaching the fracture pressure. CT scanning showed that the core volume expanded significantly after hydraulic dilation, significant deformation occurred in the horizontal direction, and secondary complex fracture network appeared inside, indicating superior dilation effect. Finally, a field case is studied to demonstrate the good results of hydraulic dilation construction in heavy oil cyclic steam stimulated wells in Bohai Oilfield. The study results provide feasibility analysis for hydraulic dilation and safe connection and high-efficiency development of heavy oil.