Since 2000, great progress has been made in China’s oil and gas exploration and development with rapid development of natural gas, large-scale development of unconventional oil and gas, and further improvement of oil and gas reserves and production increase in the onshore western region and offshore areas, basically forming a new pattern of oil and gas exploration and development strategy of “simultaneous development of oil and gas”, “promotion both conventional and unconventional resources”, “linkage between the eastern and western regions”and “overall planning of onshore and offshore areas”. The preliminary judgment of reserves and production forecast data by various methods such as reserve discovery law and life cycle in different exploration stages, suggests that the existing pattern of oil and gas exploration and development will be more prominent before 2035, which is expected to achieve “three surpassing”, that is, natural gas production (oil equivalent) will surpass oil production, increment of unconventional gas production will surpass that of conventional gas, and oil production in the onshore western region and offshore areas will surpass that in the eastern region. For oil exploration, the annual production will be stable at 2×108t for a long period, and a new pattern of “three pillars” of the eastern region, western region and offshore areas be formed. While for natural gas exploration, the annual production continues to maintain a rapid growth, reaching 3100×108m3, and a new pattern of “mainly in the western region, supplemented by offshore areas and the eastern region” be further established. At the level of government policy, following suggestions are put forward: (1) Strengthen the strategy of “stabilizing oil and increasing gas production”, vigorously develop natural gas,and accelerate the transformation to green and low-carbon energy; (2) Increase policy support for unconventional resources such as shale oil and gas, coal-bed gas, etc., and promote large-scale benefit development; (3) Strengthen risk exploration and technological research on deep formation of onshore western region and deep water areas, so as to provide a strong domestic oil and gas supply security for basically realizing the goal of modernization by 2035.

China has abundant coalbed methane (CBM) resources. Through more than 30 years of exploration and development, CBM industry in China has entered the stage of large-scale development, but the overall progress is relatively slow, which is characterized by the far less production and sales volumes than the total amount of CBM resources. This paper systematically describes the development history, policy and industry status of China's CBM industry, analyzes the corresponding problems and reasons, and further puts forward the technical and management countermeasures and suggestions for the sustainable development of CBM business. Results show the following deficiencies: (1) No detailed CBM geological study; (2) lack of the basic theoretical research and field pilot test work; (3) incomplete enterprise management mode, insufficient exploration investment, and lack of professional and technical personnel. In view of these problems, three key technical countermeasures are put forward: (1) Enhance geological evaluation of CBM resource; (2) Strengthen technical research and integrated supporting technologies; (3) Optimally select appropriate CBM development mode and field engineering scheme. Furthermore,three management measures and suggestions are proposed on the policies and regulations in recent years and the current situation of CBM companies: (1) Implement the existing policies and strengthen management; (2) Intensify the comprehensive management within the enterprise; (3) Change the understandings on the benefits of CBM development, so as to promote the CBM industry to become an important supplementary energy for the national economy. The above measures will solve the problems and promoting high-quality development of CBM business in China.

Ordos Basin is the second largest sedimentary basin in China, which has abundant oil and gas resources and broad exploration prospect. In recent two decades, growth in oil and gas reserves and production is the fastest in Ordos Basin, and now it is the largest oil and gas producing basin and the largest natural gas producing region in China. Through more than 50 years of research, Changqing Oilfield has innovated five petroleum geological understandings, including “shale oil of continental freshwater lake basin, large delta of inland depression lake basin, Jurassic paleogeomorphic oil reservoir group, continental tight sandstone gas, and Ordovician karst paleogeomorphic natural gas”. Moreover, three technology series have been developed in terms of “3D seismic exploration in loess plateau, logging identification and evaluation technology of low-permeability tight oil and gas layers, and volume fracturing of low-permeability tight reservoir”. As a result, four billion-ton-level large oil regions and three trillion-cubic-meter-level large gas regions have been discovered, contributing a lot to the national energy and resource security and providing important experience and reference for the exploration of similar basins at home and abroad.

The fault system in Shunbei area has characteristics of “zonation between the east and west” bounded by Shunbei No.1
and No.5 faults, which play a transformation role between the east and west fault systems. On the plane, the NE trending Shunbei
No.1 fault is mainly composed of pull apart segment and translation segment, where the single well controls large area of oil reservoir,while the NW trending Shunbei No.5 fault is jointly formed by north and south segments. The north segment is dominated by compression stress with relatively small-scale oil reservoir controlled by single well. The seismic interpretation of No.4, No.8 and No.12 faults indicates that the NE fault system has a typical “three-segment” feature on the plane, with intensive fault activities and similar strike with the current regional principal stress. The overall reservoir scale is large and reservoir connectivity is good in each segment. In addition, high-quality source rocks of basin-middle and outer gentle slope facies were developed in the eastern Shunbei area. As a whole, the reservoir development and hydrocarbon accumulation conditions are superior than those of the NW fault system. Based on the above understandings, Wells Shunbei 42X, Shunbei 41X and Shunbei 8X were drilled, and high oil and gas flow rates of 1000 tons of oil equivalent obtained during well testing, indicating a new resource position of (400-500)-million-ton-level oil equivalent, which further proved that the NE strike-slip fault system has large reservoir scale, superior hydrocarbon accumulation conditions, and the characteristics of five-in-one “strike-slip fault system controlling the reservoir,trap, hydrocarbon migration, accumulation and enrichment”. The result can be used for reference to evaluate the strike slip fault of marine carbonate rocks in China.

It has been known that CBM exploration is predominant in the Jinxi flexural fold belt in the eastern margin of Ordos Basin.However, due to unclear understanding of gas accumulation, there has been no major breakthrough of tight gas exploration. In 2013, CNOOC made a firm decision to shift from CBM exploration to tight gas exploration. By systematically summarizing the gas accumulation condition and gas reservoir characteristics, the company revealed the differential enrichment law of tight gas, proposed favorable areas and obtained tight gas reserves. The research result suggests that: (1) Pay zones of Linxing-Shenfu Gas Field are mainly in the Carboniferous Benxi Formation and Permian Taiyuan and Shihezi Formations, which are typical tight sandstone gas reservoirs; (2) The main source rocks are coal measure strata, with an average CH4 content of 95% and no H2S; (3) The burial depth of gas reservoir is between 1300-2200 m, and the pressure coefficient ranges from 0.85-1.01; (4) The reservoir consists of widely spread delta sandstone and barrier bar sandstone, of which the former has an average porosity of 8.8%, permeability of 1.10 mD, and pore throat radius less than 1.5 μm, while the latter has an average porosity of 7.6%, permeability of 0.59 mD, and pore throat radius less than 1.1 μm; (5) Influenced by the Lishi strike-slip fault zone in the east and the Zijin Mountain volcanic activities in the south, fault activity is strong in the east and weak in the west, while strong in the south and weak in the north. The hydrocarbon generation intensity is high in the south and gradually decreases towards the north affected by volcanic activities;(6) The study area experienced three periods of tectonic movement after hydrocarbon generating in the Late Jurassic, and the gas reservoir is dominated by vertical migration and accumulation. In Lingxing block, gas reservoir is mainly inside the source, near source and far source accumulation, whereas in Shenfu block it is mainly inside source and supplemented by near source accumulation with smaller scale of gas reservoir; (7) Three sets of key exploration technologies have been developed, which provide solid technical support for tight gas exploration and development. Until 2021, the proven natural gas reserves in Linxing-Shenfu block are 1010×108 m3 guided by above knowledge and technology and another one hundred billion cubic meters of geological reserves could be increased with the progressive exploration from south to north.

Binchang Block in the southwestern margin of Ordos Basin is with complex structural features, In 2020, Well Changtan 1, a risk exploration well drilled by Sinopec, tested commercial gas flow in the Upper Shihezi Formation, marking the natural gas breakthrough in Upper Paleozoic in the southern margin of Ordos Basin. Subsequently, several wells tested commercial gas flow or penetrated good gas shows in Upper Shihezi Formation, Lower Shihezi Formation and Shanxi Formation, showing multiple gas bearing layers of Upper Paleozoic in the complex structural zone of southern basin, which is different from the Longdong area inside basin. In order to find out gas accumulation pattern and improve understanding of the provenance system in the southern margin of the basin, in this paper, the gas accumulation conditions of Upper Paleozoic in Binchang block were systematically studied, including the regional tectonic evolution, fault activities, characteristics of coal measures source rocks, sedimentary facies, reservoir distribution, regional preservation conditions, and natural gas transportation characteristics by means of lithologic logging, formation test, chromatography-mass spectrometry analysis, logging interpretation, seismic interpretation and attribute analysis, and regional geological analogy, etc. The study results show that there are favorable geological conditions for natural gas accumulation of Upper Paleozoic in the southern basin, which is characterized by “multi-layer superposition, fault transportation, lower generation and upper storage, and stereoscopic gas accumulation”. The gas enrichment is jointly determined by the distribution of high-quality reservoirs and high angle fault transportation. The areas where large-scale delta sand bodies are developed with large thickness and good physical properties, as well as high angle faults for gas migration and accumulation are favorable targets for gas exploration.

Major breakthrough has been made in natural gas exploration of aluminiferous rock series of Permian Taiyuan Formation in Well Ninggu 3 in the southwestern Yishan Slope, which alters the traditional understanding that aluminiferous rock series can’t form effective reservoir. In this paper, research on reservoir quality, gas-bearing properties and gas accumulation characteristics has been carried out to further evaluate the potential of aluminiferous rock series and search for large-scale discovery. By using the regional geology, drilling, logging and testing data, gas accumulation conditions and pattern of aluminiferous rock series of Taiyuan Formation in Well Ninggu 3 has been studied in detail, which shows that (1) aluminiferous rock series consist of thin interbedding of bauxite, bauxitic mudstone, sandstone and tuff, and porosity-fractured reservoir is developed controlled by sedimentation and tectonism with main reservoir space of residual intergranular pore, intergranular dissolution pore, intercrystalline pore and microfracture; (2) The aluminiferous rock series is paragenetic or directly contacted with Permian coal measure source rocks, forming self-generation and self-storage type source rock-reservoir assemblage;(3) Influenced by the Indosinian-Yanshanian tectonic movement, faults and fractures are well developed, which effectively improve the hydrocarbon transport capacity. In a word, the coupling relation between “source rock, reservoir and fracture” is the key for gas accumulation. The discovery of Well Ninggu 3 expands gas exploration field in the Ordos Basin, and shows great potential and broad prospect of aluminiferous rock series.

A new evaluation method of oil and gas discovery cost based on different categories of exploration is proposed in order to properly reflect the effectiveness of oil and gas exploration, i.e., oil exploratory and natural gas exploration, which can’t be done by traditional methods.This new method covers an evaluation index system of exploration effectiveness, including twelve parameters of six categories based on different exploration categories. Firstly, relationship models of controlled, predicted and proven oil and gas reserves are established, and the weighted reserves sequence is constructed by regression analysis of reserve upgrade rate. Then the weighted discovery cost sequence is established based on the weighted reserves sequence and historical investment data. This method provides a solution for reasonable evaluation of oil and gas discovery cost of different exploration categories and eliminates the influence of fluctuating exploration rhythm and time span and lag of discovery, which can be applied to the fine preparation of exploration plan, and rapidly deploy from the reserves task to investment for different exploration categories, so as to optimally allocate the investment, and provide technical support for decision-making of oil companies at low oil price.

The exploration of subtle reservoirs in Bohai Oilfield is concentrated in the sub-lacustrine fan of Dongying Formation in Liaozhong Sag, which has greatly different results in different structural zones. The correlation study of structural framework and sedimentary system characteristics in Liaozhong Sag, and the distribution law of sub-lacustrine fan oil and gas reservoirs from well data, indicate that the enrichment degree of hydrocarbon in sub-lacustrine fan is mainly controlled by three factors, namely the accumulation capability in deep formation, thickness of regional mudstone caprock and overpressure of source kitchen. In particular, the catchment ridge formed in deep structures plays an important role in forming high-abundant external source type sub-lacustrine fan oil and gas reservoirs. Based on this understanding, hydrocarbon migration and accumulation pattern of sub-lacustrine fan oil and gas reservoirs in Dongying Formation in Liaozhong Sag is divided into three types, i.e., “catchment ridge – fault”, “transporting ridge – fault” and “source rock – fault”. The inversion type catchment ridge in the sag areas of southern sub-sag, and fault – uplifting type catchment ridge in the western slope of central sub-sag in Liaozhong Sag are favorable plays for searching for high abundant sub-lacustrine fan oil and gas reservoirs. The above migration model has a certain reference significance for the exploration of other external source type oil and gas reservoirs.

The eastern Mediterranean has become one of the global hot spots of deep-water oil and gas exploration in recent years owing to its abundant oil and gas resources and low degree of exploration. The study of deep-water hydrocarbon enrichment conditions in the Eastern Mediterranean is of guiding significance to the selection of exploration zones and plays in this area. This paper analyzes the tectonic sedimentary evolution, petroleum geological conditions, reservoir-caprock assemblages, and hydrocarbon accumulation characteristics of the Eastern Mediterranean and discusses the deep-water hydrocarbon enrichment conditions and exploration targets by comprehensive petroleum geological study on the international oil and gas commercial database and geological and geophysical data. The results show that there are two main reservoir-caprock assemblages of Miocene reef limestone + salt rock and Miocene turbidite sandstone + salt rock, and two inferred reservoir-caprock assemblages of Cretaceous turbidite sandstone + shale and Jurassic reef limestone + marl in the Eastern Mediterranean. The deep-water hydrocarbon enrichment in the Eastern Mediterranean is controlled by thick Oligocene-Miocene marine source rocks, high-quality Miocene basin floor fan turbidite sandstone and reef limestone reservoirs, regional salt caprocks and large structural traps developed during the tectonic inversion period. In the future, favorable plays of Miocene turbidite sandstone in the deep-water area in the Levant Basin and Miocene reef limestone around the Erotosthenes platform should be focused on, and new fields of Miocene turbidite sandstone in deep-water area in theHerodotus Basin and deep Mesozoic in the Levant Basin be further explored.

Horizontal well drilling combining with multi-staged fracturing is proved to be an important method for tight gas reservoir development. However, due to the strong heterogeneity of tight gas reservoir and the great difference in production contribution of each stage,accurately identifying the sweet spot interval of horizontal section and optimizing fracturing scale has become the key process to improve production capacity. The microseismic vector scanning monitoring was conducted for 57 stages in six horizontal wells, and 72 effective fractured intervals were identified. The correlation analysis of these intervals and the related parameters of wireline logging and mud logging data shows that total hydrocarbon and the rate of penetration (ROP) have the best correlation with those fractured intervals. Therefore,formula for calculating the parameter Ktr of sweet spot interval (easily fractured position) is established by using total hydrocarbon and ROP.The application result shows significantly more microseismic events in stages with abnormal Ktr than other stages in Well S-13H, indicating more initiated fractures, and three sweet spot intervals contribute more than 90% of the total production. In addition, production has a good relationship with the sweet spot interval identified by Ktr value in another five horizontal wells without microseismic monitoring data. It is verified that the Ktr method can accurately identify the sweet spot interval in horizontal section, which has guiding significance for selecting the fracturing stage and technology optimization of horizontal wells.

The dolomite reservoirs of the Lower Cambrian Xiaoerbulake Formation and the Sinian Qigebulake Formation are developed in the platform-basin area in the Tarim Basin, which are close to the source rocks of the Lower Cambrian Yuertusi Formation. The favorable target area is 27500 km2 and it has a broad exploration prospect. However, the geological conditions in this area are very complex. The lithology difference between the upper and lower strata is large. Faults are developed in some strata and the pressure system is complex. In addition,igneous rocks are developed with poor drillability. The complex geological conditions and ultra-high pressure and ultra-high temperature make the drilling face great challenges. Through the research on wellbore structure design based on the integration of geology and engineering,the company has developed wellbore structure design technologies which are suitable for ultra-deep well drilling. Through lab test of rock mechanics characteristics of special formation rocks, it has developed the personalized design and selection of drilling bits combining with the rock breaking characteristics of the strata, and the hydraulic and mechanic parameters have been optimized based on the optimal rock breaking law. Meanwhile, based on the formation lithology characteristics and wellbore stability analysis, the drilling technology has been improved. By continuous research and improvement, the Tarim Oilfield possesses the supporting technology for drilling ultra-deep wells over 8000 m, and capable of drilling wells up to 9000 m. The completion of the Asia's deepest well with a depth of 8882 m, Well Luntan 1, effectively promotes the exploration process of the deep strata and strongly supports the discovery of replacement areas for increasing reserves and production in the Tarim Basin.

Microbial oil and gas detection technology can predict the occurrence and distribution of oil and gas reservoirs, which has the characteristics of less multi-solution, fast and economic. This technology adopts microbiological and geochemical methods to detect the number and community structure of exclusive microorganisms of sediment samples collected from surface soil or seabed. In recent years,key technologies such as the rapid on-site microbial detection and environmental factor correction have made important progress through continuous research and development, improving the prediction accuracy, reliability, and exploration efficiency. It has been applied in many fields in the Junggar Basin, such as deep structure, volcanic rock, and lithologic reservoir, which successfully predicted oil and gas bearing potential of several risk exploration wells, i.e., Wells GT1 and CT1, providing a new method and model for rapid evaluation of oil and gas bearing potential in new areas with complex geological and surface conditions. Therefore, it has broad application prospects in the exploration of structural reservoirs of lower assemblage in the southern margin, Carboniferous volcanic reservoirs in the northwestern margin, and Jurassic and Permian lithologic reservoirs in eastern margin of the Junggar Basin. However, the application of this technology has deficiency in bedrock exposed area, quicksand area, heavy oil reservoir with lack of light hydrocarbon and other areas, as well as in identifying the depth and horizon of oil and gas reservoirs.