Since 1993, Chinese oil corporations have started the pace of “going global”, with E&P activities spreading all over the world over the past 29 years, from land to deep-water, and from conventional to unconventional oil and gas fields, growing to be the major participants of international oil and gas industry. The experience of overseas E&P is divided into four stages, i.e., exploratory stage, rapid development stage, large-scale development stage, and optimization and adjustment stage. It is now an important way to ensure the national energy security given the rising oil and gas external dependence of China. In 2020, the total overseas equity oil and gas production of CNPC, Sinopec and CNOOC was up to 167 million tons oil equivalent. Guided by the goals of “double carbon” and national energy security, it is still a major task to obtain more overseas resources. However, there are series of challenges, such as the geopolitics, shrinking exploration blocks, insufficient reserves, rapid natural decline of production, and difficulty in assets optimization. By benchmarking with the major IOCs, several strategies are proposed for Chinese oil corporations, including quickly building large-scale production areas, increasing new project acquisition, especially from the “Belt and Road” countries, conducting more reliable evaluation and being cautions in acquiring unconventional oil and gas projects, strengthening the disposal of marginal assets, so as to promote high-quality development of overseas oil and gas business.

Deepwater field is one of the three global hot spots for oil and gas exploration. Based on the theory of plate tectonics, the distribution of global deep-water basins is characterized by “three in longitudes and two in latitudes”. “Three in longitudes” are three nearly N-S direction deep-water basin belts in the Atlantic continental margin, the East Africa continental margin and western Pacific continental margin. “Two in latitudes” are E-W direction deep-water basin belts in the Neotethyan tectonic domain continental margin and the circum-Arctic Ocean continental margin. Totally 15 giant-large sized oil and gas discoveries have been proved in five basin belts. The study shows that the formation of giant-large sized oil and gas regions is controlled by three factors. The primary factor is the development of world-class source rocks of large-area lacustrine facies, marine and continental transitional facies, and marine facies. The lacustrine source rocks are mainly deposited in South Atlantic continental marginal basins; The marine source rocks are distributed in North Atlantic and East African continental marginal basins; While the transitional source rocks are mainly distributed in western Pacific continental margin and Neotethyan tectonic domain continental margin of large coal measure river delta facies. The second factor is the development of world-class high-quality reservoirs, including two types of clastic rock and carbonate rock. The clastic reservoirs are mainly turbidite fan controlled by large river-delta, while carbonate reservoirs are related to shell limestone. The third factor is the development of world-class trap groups, such as salt structural trap, gravity detachment structural trap, giant thrust nappe structural trap, and large turbidite lithologic trap, etc. The global oil and gas exploration in deep-water basins is unbalanced and inadequate, and there are four strategic fields in the future, i.e., strategic expansion, strategic breakthrough, strategic discovery and strategic preparation. The exploration orientation for strategic expansion includes the proven hydrocarbon rich plays in the proven giant-large oil and gas regions, which is the main field to obtain reserves with low investment risk and quick results at present. The exploration orientation for strategic breakthrough mainly includes new confirmed plays in the proven giant-large oil and gas region with proven source rock conditions, which has a low risk to achieve commercial discovery. The exploration orientation for strategic discovery is the potential oil and gas area with oil and gas shows or potential commercial discovery, which has the potential of large-scale discovery. The exploration orientation for strategic preparation is the area that has no but the possibility to find major discoveries. On the whole, the global oil and gas exploration in deep-water basins has a huge potential.

In the past 10 years, global oil and gas exploration experienced the double test of twice sharp falls of oil prices and “carbon neutralization”, and the exploration investment was continuously reduced; Meanwhile, the continuous development of oil and gas geological theory and exploration technology resulted in the great improvement of exploration efficiency. As a whole, global oil and gas exploration shows five remarkable characteristics: (1) The number of oil and gas discoveries has been decreasing, but the average size continuously been increasing; (2) The new discovery of natural gas has been maintained at a high level of more than 60%, growing to be a major direction of reserve growth; (3) Deep water/ultra-deep water has become the most important areas for increasing reserves, and multiple new exploration areas have been identified; (4) The new discoveries have gradually shifted from the middle-shallow formation to the deep/ultra-deep formation, and new breakthroughs have been made in the offshore area and onshore area; (5) The discoveries of giant oil and gas fields have remained at a relatively high level. The new discoveries from venture exploration in frontier areas contribute 58% of the total oil and gas discoveries, and the new reserves from rolling exploration in mature basins contribute 42% of the total reserve volume. The maturity of global oil and gas exploration is still at a medium-low level, and the exploration potential is great in the future; The frontier region is the main areas for oil and gas exploration, which should be deployed in advanced; Deep water, deep formation and natural gas areas are important exploration orientations in the future. Furthermore, it is suggested that 10 areas deserve special attention, such as the Russian Arctic, Somali offshore areas and the periphery of the Caribbean Sea.

The development and construction of a global petroleum geology and resource assessment data platform have great significance to the global petroleum resource assessment and effective use of overseas petroleum resources. By applying the platform-based development strategy, a general database is primarily developed to customize development and operation management platform. Then various types of application databases and application software are developed on this platform, so as to develop and construct the global petroleum geology and resource assessment database, as well as an advanced conventional-unconventional resource evaluation software system, which will provide a powerful support for the global petroleum resource evaluation and favorable exploration zone selection, and boost the development of overseas oil and gas business of CNPC.

The carbonate-evaporite paragenetic deposits are developed in the Ordovician Majiagou Formation in Ordos Basin. The fourth member of Majiagou Formation (Ma 4 member) is composed of a set of transgressive carbonate rocks with the largest thickness in Majiagou Formation, which has always been the target layer for natural gas exploration. Based on geophysical, drilling, core samples and organic geochemical data, the hydrocarbon accumulation conditions such as paleo structure, reservoir distribution, source rocks and trap are restudied, and the following achievements are obtained: (1) Natural gas in Ma 4 member is oil-type gas, generated by marine source rock of the subsalt Ordovician. In addition to conventional kerogen, the source rock has a large amount of parent materials for hydrocarbon generation, such as the dispersed organic matter and organic acid salt, showing great potential of hydrocarbon generation; (2) In the Ordovician, two secondary structural units, Wushenqi-Jingbian paleo uplift and the eastern subsalt low uplift, were developed in central-eastern depression in Ordos Basin, which controlled the development of dolomite reservoir in the intra-platform shoal and intra-platform mound of Ma 4 member, with the main reservoir space of intergranular pores; (3) The wide spread self-generation and self-storage type lithologic gas reservoir is formed in the central-eastern Ordos Basin by marine source rocks of subsalt Ordovician, reservoir of the intra-platform shoal and intra-platform mound dolomite of Ma 4 member, and cap rocks of the overlying thick evaporites and the lateral barrier provided by tight limestone in the updip direction. Guided by the new geological understanding, the risk exploration Well MT1 was drilled targeting at Ma 4 member, in which a gas layer of 43.4 m was penetrated, and high gas flow of 35.24×104 m3/d was tested by applying new hydraulic sand fracturing technology, achieving a major breakthrough in strategic replacement field in the basin.

In recent years, major oil and gas discoveries have continuously been made in South America. Relevant research works are conducted on the basis of previous geological studies to understand the spatial distribution and the amount of undiscovered oil and gas resources in South America, so as to provided reference for the selection of strategic exploration area. Controlled by the regional tectonism such as subduction of the Pacific Plate and pull apart of the South Atlantic, the South American continent has different tectonic evolution characteristics of its eastern, western, southern and northern structural parts, developing various types of sedimentary basins such as craton,fore-arc, back-arc, foreland and passive continental margin. The statistical analysis of the distribution of discovered oil and gas fields in various countries, basins and reservoir formation shows that the oil and gas resources are widely distributed in South America with various degrees of enrichment. Most of the oil and gas reserves are concentrated few countries. The oil and gas resources are the most abundant in two types of basins, i.e., the foreland basins of collision continental margin in the western South America and the passive continental margin basins on the eastern Atlantic coast, with the main reservoir of the Mesozoic sandstone and carbonate rocks. The trap evaluation method and analogy method are applied to estimate the undiscovered resources in 56 petroliferous basins with different exploration levels. The results show that it still has great potential for oil and gas exploration in South America, with the undiscovered recoverable oil and gas resources of 50.35 billion tons of oil equivalent. The future exploration will focus not only on basins with high exploration level, but also on those with low exploration level.

Natural gas resources are abundant in Amu Darya Basin in the Central Asia, and faults play an important role in subsalt Jurassic gas enrichment. By analyzing 3D seismic data, core samples and production performance in the eastern part of the right bank of Amu Darya River, the control effects of faults with different scales on the reservoir development and gas enrichment in the Callovian-Oxfordian carbonate reservoirs are systematically studied. The result shows that two groups of reverse faults in NE and NEE directions and four groups of strikeslip faults in NWW, EW, NNW and SN directions are developed in subsalt carbonate rocks, with structural types characterized by reverse faults related folds involved by basement and the compression-torsion related positive-flower structures. Faults were mainly formed in the Neogene,of which the NEE direction reverse faults were developed by the compression in the early Himalayan stage, and the NE direction reverse faults and strike-slip faults were formed in compression-torsion stress field in the middle-late Himalayan movement. Faults are distributed in zones in N-S direction bounded by A-Gao sinistral strike-slip fault belt. Among them, reverse faults are dominated by NE direction in the south side, while they gradually change to NEE direction in the north side. The SN trending strike-slip faults are mainly distributed to the east of Ma-Huo fault belt. Based on the scale, faults are divided into four categories, i.e., fault controlling structural belts, fault controlling traps, secondary fault in structures and micro fault. Faults of the first three categories mostly extend from basement to salt-gypsum rocks and control the development of fractured-vuggy reservoirs and the migration of natural gas. The higher the activity intensity of faults, the more developed the fracturedvuggy reservoir and the higher degree of gas enrichment. Three types of favorable zones are classified according to fault characteristics. Type Ⅰ is the large-scale fractured-vuggy gas reservoir development zone with strong gas-charging adjacent to fault controlling structural belts and fault controlling traps. Type Ⅱ is the fractured-vuggy gas reservoir development zone with partial weak gas-charging adjacent to the secondary faults in structures. Type Ⅲ is the fractured-porosity type or fractured gas reservoir development zone adjacent to micro faults. Among them, Type Ⅱ gas reservoir development zone is the key exploration target in the near further.

Baobab structural zone is located in the slope of northeastern Bongor Basin, Central African Rift System. Although it is relatively far away from the basin center, the exploration practice shows that it is the most proliferous area in Bongor Basin. A detailed analysis on structural evolution and controlling factors of hydrocarbon accumulation will provide good reference for petroleum exploration in the Central African Rift System. The structural evolution and oil and gas distribution characteristics in Baobab structural zone are studied to identify the controlling factors of hydrocarbon accumulation. The results show that Baobab structural zone has experienced five main evolution stages, i.e., pre-rift stage, rift stage, depression stage, inversion stage and extinction stage. The deep lacustrine mudstones of the Lower Cretaceous M and P Formations are stably distributed in the rift basin, which are not only the main source rocks, but also good regional caprocks. A series of anticline or fault anticline traps were formed in Baobab structural zone affected by the large-scale structural inversion and strata denudation during the inversion period in the Late Cretaceous, which was conducive to the hydrocarbon accumulation. In the structural highs or bulge areas, buried hill oil reservoirs are developed mainly in bedrock weathering crust and fracture development zone, of which the trap formation, hydrocarbon migration and reservoir transformation are controlled by fault activities. While in subsags close to the bulge area, turbidite channel and fan delta sandstone reservoirs are developed of P Formation, forming oil reservoirs controlled by structure and lithology. As a whole, oil and gas distribution law is characterized by bedrock buried hill oil reservoir in the bulge area, while inside-source P Formation oil reservoir in the subsag area.

Duvernay shale is the most important shale series for oil and gas enrichment and production in the Western Canada Sedimentary Basin. It is a set of asphaltene rich dark shale formed during the maximum transgression period. Different from the domestic shale oil and gas reservoirs, Duvernay shale gas reservoir is characterized by high condensate content, great variation in condensate to gas ratio on the plane, and complex fluid distribution. The tectonic and sedimentary evolution, stratigraphy, geochemistry, reservoir characteristics, and fluid distribution of the Upper Devonian Duvernay shale in Simonette block in the Western Canada Sedimentary Basin are analyzed, and the exploration and development strategy of liquid-rich shale is proposed. The study results show that: (1) The upper part of Duvernay shale in Simonette block has large reservoir thickness, no carbonate interlayers, high TOC content, and good reservoir physical properties, which is the main exploration and development target layer; (2) Duvernay shale in Simonette block is located in a liquid-rich zone, with vitrinite reflectance (Ro) between 1.1%-1.6%, which is divided into three zones based on the condensate to gas ratio, namely the volatile oil zone, ultra-high gas condensate content zone and high gas condensate content zone. As the condensate-to-gas ratio (CGR) increases, the methane content gradually decreases, the crude oil density gradually increases, and the oil recovery factor gradually decreases; (3) In terms of exploration and development strategies, priority should be given to evaluation and development of ultra-high gas condensate content and high gas condensate content zones which are easier to be produced and have a high degree of producing rate, and followed by the volatile oil zone. Vertically, the high TOC shale layers are focused as the main targets.

There are significant differences in geological characteristics of low-rank coal seams in Surat block on the eastern margin of Surat Basin, Australia. The optimal selection of favorable exploration area is the key to realize the large-scale and benefit CBM development in the study area. Based on a large number of logging, core lab test and well testing data, fine characterization of multiple and thin coal seams is conducted of a huge thick coal measure strata, and the spatial distribution of coal reservoir properties is quantitatively analyzed, such as coal thickness, gas content, and permeability. Based on the 3D geological model, the study area is divided into three classes of zones according to the spatial distribution of coal reservoir properties. Class I zone is located at the structural high on the slope and adjacent to the denudation zone, and the CBM reservoir is characterized by high permeability and high resource abundance, with coal seam thickness of 18-40 m (burial depth≥150 m), dry ash-free gas content of 3.8-6.5 m3/t, permeability of 20-500 mD (average 250 mD), which is the most favorable area for the large-scale development in the near future. Class Ⅱ zone is located at the denudation zone on the top of the slope, and the CBM reservoir is characterized by high permeability and low resource abundance, with coal seam thickness of 8-20 m (burial depth≥150m), dry ash-free gas content of 2.8-4.2 m3/t, and permeability of 500-900 mD (average 680 mD), which is a potential area. ClassⅢ zone is located at the structural low on the slope, and the CBM reservoir is characterized by medium-low permeability and high resource abundance, with coal seam thickness of 18-41 m, dry ash-free gas content of 4.8-7.8 m3/t, permeability of 0.1-20 mD (average 5 mD), and poor natural recoverability. The classification of exploration zone shows that the ClassⅠzone is a favorable area for capacity construction in the study area; ClassⅡ zone is the replacement and supplement area in the middle and late development stage of ClassⅠzone; ClassⅢ zone has relatively low permeability, and small well spacing development can be applied to increase gas production.

The Sumatra Basin is the largest hydrocarbon rich region in Indonesia, but the exploration result is getting worse with the continuously deep exploration, indicating a bottleneck period of oil and gas exploration. Based on the study of geological characteristics and resource potential of the basin, the possible exploration fields are predicted. The results show that the basin has experienced three stages of tectonic evolution during the Cenozoic, namely the Middle Eocene-Oligocene syn-rift stage, the Early-Middle Miocene post-rift stage and the Late Miocene-present compression stage; Three types of source rocks are developed, namely the lacustrine source rocks in Central Sumatra Basin, marine source rocks in North and South Sumatra Basin, and marine continental transitional source rocks in South Sumatra Basin; Structural trap is the main trap type in the basin. The oil and gas reservoirs are distributed around the hydrocarbon generation center, which migrated vertically to the trap through oil-source faults and accumulated in reservoirs; The cumulative undiscovered oil resources are 23.67×10⁸bbl, and the undiscovered natural gas resources are 11.26×10¹²ft³, which still have great exploration potential as well as resource foundation for forming medium and small-scale oil and gas reservoirs. The Middle-Upper Miocene and buried hills in the central structural belt are the main fields for rolling exploration; The Oligocene reef/carbonate buildup in the northern structural belt is a major field for risk exploration, which is also a field to discover large-medium sized oil and gas reservoirs.

Oil and gas have continuously been discovered in the Middle-Lower Carboniferous carbonate rocks (KT-Ⅱ layer) in the eastern margin of Pre-Caspian Basin. With the progress of exploration, the prediction of thin carbonate reservoir is facing challenges. By starting from the paleogeomorphology before the deposition of KT-Ⅱ layer, the depositional settings during the deposition of carbonate rocks is restored, and the law of reservoir distribution is identified. The KT-Ⅱ layer is subdivided into three third-order sequences from bottom to top, i.e., SQ1, SQ2, and SQ3. Based on the fine seismic interpretation of high-frequency sequence, the paleogeomorphology before the deposition of each sequence was restored by using the methods of seismic horizon flattening, residual formation thickness and moulage. The beach body of SQ1 was mainly deposited around the slope break zone, with a large thickness in local area; The beach body of SQ2 was mainly distributed in slope zone between the low potential area and the high potential area, with continuous distribution and more developed reservoir towards the high potential area; While the beach body of SQ3 was mainly deposited in slope zone between two strike-slip faults.

The drilling cost accounts for 40%-50% of the total well construction cost in unconventional oil and gas development, therefore, reducing drilling cost is very crucial to save well construction cost and improve development benefit. The optimal and fast drilling technology for middle-deep formation in Groundbirch tight gas project in Canada is introduced to provide technical reference for unconventional oil and gas horizontal well drilling in China. The specific parameters are as follows: Two sections of slim hole with horizontal section of 2200-3500 m. The first section is 222.3 mm borehole with 177.8 mm surface casing and the second section is 159.0 mm borehole with 114.3 mm production casing; The batch drilling model is applied and drilling fluid is recycled. The first section is spudded within 2hrs, and second section within 1 day; The spoon shaped well trajectory is designed by considering anti-collision, enhancing ROP, and decreasing friction drag, and the target displacement is reduced to increase the reservoir production area. The single bend screw + MWD is applied to control the well trajectory, and the Compass Software is used for anti-collision scanning. When the separation coefficient is less than 1.0, the SAG and MAG errors are corrected to ensure the safe drilling and avoid obstacles. During horizontal section drilling, the oil-based drilling fluid, high torque screw, hydro-oscillator, 52 MPa drilling pump, surface manifold and pressure control technology are adopted. Furthermore, the high rotary speed and large WOB are applied to achieve one trip completion of the horizontal sections of most horizontal wells, with the maximum daily footage of 1152 m, and ROP reaching up to 65.59 m/hr; Based on pressure distribution of wellbore and water hammer effect during fracturing, the production casing is differentially designed for different sections to save costs; From the second section, the well trajectory is designed with 8°-13° deviation section, and the floatation collar and special Tesco tool are used to running casing to greatly reduce the friction drag. The number of centralizers is increased to ensure cementing quality and greatly improve the casing running efficiency. Through the continuous optimization and improvement, the average drilling time was only 14.4 days of 14 wells drilled after Y2017 with the total well depth of 5687 m and horizontal section of 3182 m. The drilling cost per meter was decreased by 33% given that the length of horizontal section was increased by 1332 m of 158 wells drilled before 2014.

Compared with clastic reservoir, carbonate reservoir has strong heterogeneity and complex pore structures, as well as wide distribution range of pore-throat radius and poor relationship between conventional porosity-permeability based on the classification of sedimentary facies zone. Therefore, the modeling method of reservoir petrophysical properties controlled by sedimentary facies is not applicable. By taking the Cretaceous Mishrif Formation in Iraq H Oilfield as an example and using seismic data, well logging, geology, and dynamic performance of oil reservoir, the fine reservoir evaluation and oil reservoir description are conducted, and the internal genetic relationship between petrophysical facies and sedimentary facies is studied on the basis of rock type classification. Then the rock type model controlled by sedimentary facies model is established, and porosity, permeability and oil saturation models are established for different rock types. Following, the static and dynamic information are combined to characterize the distribution of barriers, interlayers and high permeability strips to correct the permeability model. Finally, a 3D geological modeling method for bioclastic limestone oil reservoir is developed based on the hierarchical control of sedimentary facies and rock types. The verification results show that the geological modeling method is reliable and can fully reflect the reservoir heterogeneity, with the fitting rate of each dynamic index reaching up to 65% in the first run of numerical simulation.