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In response to the problems of unclear distribution of deep-water pre-salt carbonate reservoirs and formation conditions of large oil fields in the Santos passive continental margin basin, based on comprehensive utilization of geological, seismic, and core data, and reconstruction of Early Cretaceous prototype basin and lithofacies paleogeography, it is proposed for the first time that the construction of pre-salt carbonate build-ups was controlled by two types of isolated platforms: inter-depression fault-uplift and intra-depression fault-high. The inter-depression fault-uplift isolated platforms are distributed on the present-day pre-salt uplifted zones between depressions, and are built on half- and fault-horst blocks that were inherited and developed in the early intra-continental and inter-continental rift stages. The late intra-continental rift coquinas of the ITP Formation and the early inter-continental rift microbial limestones of the BVE Formation are continuously constructed; intra-depression fault-high isolated platforms are distributed in the current pre-salt depression zones, built on the uplifted zones formed by volcanic rock build-ups in the early prototype stage of intra-continental rifts, and only the BVE microbial limestones are developed. Both types of limestones formed into mound-shoal bodies, that have the characteristics of large reservoir thickness and good physical properties. Based on the dissection of large pre-salt oil fields discovered in the Santos Basin, it has been found that both types of platforms could form large-scale combined structural-stratigraphic traps, surrounded by high-quality lacustrine and lagoon source rocks at the periphery, and efficiently sealed by thick high-quality evaporite rocks above, forming the optimal combination of source, reservoir and cap in the form of “lower generation, middle storage, and upper cap”, with a high degree of oil and gas enrichment. It has been found that the large oil fields are all bottom water massive oil fields with a unified pressure system, and they are all filled to the spill-point. The future exploration is recommended to focus on the inter-depression fault-uplift isolated platforms in the western uplift zone and the southern section of eastern uplift zones, as well as intra-depression fault-high isolated platforms in the central depression zone. The result not only provides an important basis for the advanced selection of potential play fairways, bidding of new blocks, and deployment of awarded exploration blocks in the Santos Basin, but also provides a reference for the global selection of deep-water exploration blocks in passive continental margin basins.

The East African Rift System (EARS) is the youngest rift with the eastern and western branches, consisting of multiple secondary rifts. It is generally characterized by low extent of exploration and great exploration potential. Identifying the differences in hydrocarbon accumulation conditions in various rifts is very important in providing guidance for hydrocarbon exploration and selecting favorable exploration targets in this area. Based on the interpretation of first-hand seismic-geological data, and combining other materials such as commercial databases and open access literature, the structural characteristics of the main rifts in the eastern and western branches of the EARS are comparatively analyzed; based on the anatomy of the discovered hydrocarbon reservoirs, the rifts of the EARS are classified into four types depending on their structural styles, including double-fault type, simple single-fault type, single-fault transfer type, and single-fault terrace type, and the control of structural style over hydrocarbon accumulation in the EARS is discussed. In the Western Branch of the EARS, large rifts such as the Albertine Rift and the Tanganyika Rift are mainly of double-fault type and single-fault transfer type, and only some small rifts are of the simple single-fault type. The rifts in the Eastern Branch of the EARS are generally small; the rifts in the northern section of the Western Branch are mainly of the simple single-fault type, and those in the southern section are mainly of the single-fault terrace type. The hydrocarbon potential of double-fault rifts is the greatest, followed by that of simple single-fault rifts and single-fault transfer rifts, and the hydrocarbon potential of single-fault terrace rifts is relatively limited. The results obtained from a comparative analysis of the structures, sediment fills, and reservoir elements of various rifts show that the west side of the Albertine Rift, the southeast of the Tanganyika Rift, the Kerio Rift, and the land in the northwest of the Turkana Rift have great exploration potential.

The global trends in deepwater oil and gas exploration, characteristics of deepwater oil and gas discovery, and layout of deepwater oil and gas exploration business by seven major international oil companies are systematically analyzed using commercial databases (e.g. S&P Global and Rystad) and public information of oil companies. The deepwater area is currently the most important domain for global oil and gas exploration and discovery, with the most discoveries and reserves in passive continental margin basins. The deepwater discoveries have the greatest contribution to the total newly discovered oil and gas reserves in the sea areas, with an increasing number of lithological reservoirs discovered, and oil and gas discoveries mainly distributed in the Mesozoic–Cenozoic. The seven major international oil companies are widely active in various aspects of deepwater oil and gas exploration and development, and play a leading role. Based on years of theoretical understanding of global oil and gas geology and resource evaluation, it is proposed that favorable deepwater exploration areas in the future will mainly focus on three major areas: the Atlantic coast, the Indian Ocean periphery, and the Arctic Ocean periphery. Six suggestions are put forward for expanding overseas deepwater oil and gas exploration business: first, expand the sources for obtaining multi-user seismic data and improve the scientific selection of deepwater exploration areas; second, increase efforts to obtain deepwater exploration projects in key areas; third, adopt various methods to access into/exit from resource licenses flexibly; fourth, acquire licenses with large equity and operate in “dual-exploration” model; fifth, strengthen cooperation with leading international oil companies in deepwater technology; and sixth, improve business operation capabilities and gradually transform from “non-operators” to “operators”.

The global exploration investment, new oil and gas discoveries, exploration business adjustment strategies of oil companies in 2021, and future favorable exploration domains are systematically analyzed using commercial databases such as IHS and public information of oil companies. It has been found that the world oil and gas exploration situation in 2021 has continued the downturn since the outbreak of COVID-19. The investment and drilling workload decreased slightly, but the success rate of exploration wells, especially deepwater exploration wells, increased significantly, and the newly discovered reserves increased slightly compared with last year. Deep waters of the passive continental margin basins are still the leading sites for discovering conventional large and medium-sized oil and gas fields. The conventional oil and gas exploration in deep formations of onshore petroliferous basins has been keeping a good state, with tight/shale oil and gas discoveries made in Saudi Arabia, Russia, and other countries. While strengthening the exploration and development of local resources, national, international, and independent oil companies have been focusing on major overseas frontiers using their advantages, including risk exploration in deep waters and natural gas. Future favorable exploration directions in the three major frontiers, the global deep waters, deep onshore formations, and unconventional resources, have been clarified. Four suggestions are put forward for the global exploration business of Chinese oil companies: first, a farm in global deepwater frontier basins in advance through bidding at a low cost and adopt the “dual exploration model” after making large-scale discoveries; second, enter new blocks of emerging hot basins in the world through farm-in and other ways, to find large oil and gas fields quickly; third, cooperate with national oil companies of the resource host countries in the form of joint research and actively participate exploration of deep onshore formations of petroliferous basins; fourth, track tight/shale oil and gas cooperation opportunities in a few countries such as Saudi Arabia and Russia, and take advantage of mature domestic theories and technologies to farm in at an appropriate time.

In this paper, we study the structural characteristics and sedimentary filling differences of the passive continental margin basins of East Africa and establish hydrocarbon accumulation models in different basins. In the research process, the research methods of prototype basin and lithofacies paleogeography restoration, oil and gas reservoir anatomy, two-dimensional seismic data interpretation, etc. The passive continental margin basins in East Africa are divided into four types of passive continental margin basins, namely “rifted type,” “depressed type,” “faulted depression type,” and “reformed delta type,” based on the three prototype stages of intracontinental aborted rift, intracontinental-intercontinental rift, and passive continental margin basin, and the difference in sedimentary filling thickness between rift and depression periods. Finally, the accumulation models of different types of basins are established, and the favorable accumulation combinations and future exploration directions are discussed.

Based on regional geology, 2D seismic and ocean drilling data, the formation of the Eratosthenes Seamount (ESM) and its surrounding isolated platforms, types of organic reefs and hydrocarbon accumulation conditions in the eastern Mediterranean were analyzed through fine tectonic interpretation and seismic facies study, and the future exploration targets were pointed out. The formation and evolution of the ESM and its peripheral isolated platforms are highly related to the open and close of the Neotethyan ocean. The precursors of the ESM and its peripheral isolated platforms are both horst-type fault blocks formed in the Middle Triassic–Early Jurassic intracontinental rift stage. The ESM and its peripheral isolated platforms underwent continued and inherited carbonate build-ups during the Middle Jurassic intercontinental rift stage, the Late Jurassic–Late Cretaceous Turonian passive drift stage, and Late Cretaceous Senonian–Miocene subduction stage, as well as medium-slight inversion transformation beginning in the Late Miocene Messinian caused by the closure of the Neotethyan ocean. Three types of isolated platforms formed controlled by variant paleo-tectonic settings: the first type is composed of a single patch-like reef controlled by a small-scale and narrow horst-type fault block, the second type consists of a single atoll controlled by a middle-scale and wide horst-type fault block, and the third type is comprised of multiple reef-beach complexes controlled by a large-scale and broad paleo-high. The first two types universally developed in the highs of the alternate sag-uplift structural zones on the south and west of Eratosthenes, and the third type only developed in the ESM. As a result of fluctuation of sea level, two sequences of reef build-ups, i.e. the Middle Jurassic Bajocian–Upper Cretaceous Turonian and the Miocene, developed in the ESM as well as the highs in the alternate sag-uplift structural zones on the south and west of Eratosthenes. Drillings have confirmed that the first two types of isolated platforms with a single patch-like reef and a single circle-like reef have good conditions for natural gas accumulations. The isolated platform of reef-beach complexes in the ESM also has accumulation potentials of natural gas and is worth prospecting.

Zagros Basin is one of the essential basins in the Middle East with the giant oil and gas reserves. It is indicated by regional tectonic and sedimentary evolution, basin structural division, petroleum distribution characteristics and main controlling factors of petroleum accumulation. It has experienced four significant phases which are early Paleozoic intra-Cratonic pull apart basin and platform margin basin, late Paleozoic platform margin basin, Mesozoic passive continental margin basin, and Cenozoic foreland basin. The Zagros Mountain Front Fault and High Zagros Fault divided the basin into foredeep zone, simply folded zone, and Zagros thrust fault zone from southwest to northeast. The oil fields are mainly located in the foredeep zone, while the gas fields are mostly in the simply folded zone and few fields are in the Zagros thrust fault zone. The Lower Cretaceous Kazhdumi Formation mudstone is the main source rock for the Mesozoic, and Cenozoic reservoirs and the Silurian Gahkum Formation mudstone is the main source rock for the Paleozoic reservoirs. The Cenozoic carbonate is main reservoir followed by the Cretaceous Sarvak and upper Permian Dalan carbonate. The evaporite and mudstone are the main seal in the foredeep zone, while the mudstone in the simple anticline zone. The anticline structure and the seal type is the main controlling factor for the petroleum accumulation. Keywords: Zagros Basin, Structure division, Zagros Mountain Front Fault, High Zagros Fault, Evaporite

By using geologic and seismic data, this study restored the proto-type basins and lithofacies paleogeography of the Levant basin in Eastern Mediterranean during main geological periods, carried out comparison analysis on the basin architecture characteristics, and based on careful examination of the characteristics of discovered gas reservoirs, established the reservoir forming pattern and discussed the favorable reservoir forming combinations and future exploration direction in this region. Three structural architectures can be identified in the basin, the early-stage faults, the mid-stage faults and the late-stage faults. The early-stage faults are mainly controlled by intercontinental depression, which were less influenced by later compression stress in the southern deep water area of the basin. Controlled by the lateral structural stress and the Syrian Arc Fold Belt, the mid-stage faults became less active from north to south and from east to west. Influenced by the collision and/or Dead Sea strike-slip Fault Zone, the late-stage faults were active but did not pierce the thick Upper Miocene evaporites. Combined with the discovered reservoirs and outcrops, the Mesozoic sandstones and carbonates in deep water area near Eratosthenes seamount of Israel offshore and the Cenozoic carbonates and Tamar sands of Lebanon offshore are the main petroleum exploration targets in the next step. Key words: Eastern Mediterranean, lithofacies paleogeography, basin architecture, Levant Basin, deep water sedimentation, petroleum exploration direction

The basins of the South Atlantic passive margins are filled with early rifting stage lacustrine sediments (Barremian, 129–125 Ma), transitional lacustrine and marine sediments (Aptian, 125–113 Ma), and drift stage marine sediments since early Cretaceous (Albian, 113 Ma). The South Atlantic margins can be divided into three segments by the Rio Grande Fracture Zone and the Ascension Fracture Zone according to variations in the basin evolution history and configuration style. The lacustrine shale and marine shale source rocks are developed in the rift stage and drift (post-rift) stage in the South Atlantic passive margins, respectively. The southern segment of the margins is dominated by the lacustrine sedimentary filling in the rifted stage overlain by a thin marine sag system as a regional seal, where the hydrocarbons are mainly accumulated in the structural-stratigraphic lacustrine reservoirs formed in the rift stage. The middle segment developed salty rift-sag-type basins with rift and sag systems and with salt deposited in the transitional intercontinental rift stage, where the lacustrine shale in the lower part of the rifted lacustrine sequence and the marine shale in the lower part of the sag sequence formed in the marine post-rift stage are high-quality source rocks. This segment in the middle is mainly dominated by pre-salt lacustrine carbonate and post-salt marine turbidite plays. The northern segment is characterized by sag-type basins with a narrowly and locally distributed rifted lacustrine system and its overlying widely distributed thick marine sag systems. Gravity-flow (mostly turbidite) marine sandstones as good reservoirs were extensively developed in the sag stage due to the narrow shelf and steep slope. The post-rift marine shales in the lower part of the sag sequence are the main source rocks in the northern segment and the hydrocarbons generated from these source rocks directly migrated to and accumulated in the deep marine turbidite sandstones in the same sag sequence formed in the drift stage. From southern segment to northern segment, source rocks and hydrocarbon accumulations tend to occur in the stratigraphically higher formations. The hydrocarbon accumulations in the southern segment are mainly distributed in the rifted lacustrine sequence while that in the northern segment primarily occur in the post-rift marine sequence.

Sixty-six passive continental margin basins around the world were compared comprehensively from the aspect of seismogeology on the basis of plate tectonics. According to their textural and structural differences, passive continental margin basins were classified into seven subdivisions, i.e., rifted basin, non-saline faulted depression basin, saline faulted depression basin, non-saline depression basin, saline depression basin, delta reformed basin and positive reverse deformed basin. The passive continental margin basins around the world have been generated with the formation of Mesozoic and Cenozoic Atlantic and Indian Oceans and they have experienced superimposition of three prototypes, including intra-continental rift in rifting period, intercontinental rift in transitional period and passive continental margin in drifting period. In rifted basins, the petroleum systems are mainly located in the lower lacustrine/marine rift series of strata and the thinner depression series of strata at the upper part are only regional cap-rocks. Large oil and gas fields are mainly concentrated in structural traps of rift series of strata. In non-saline faulted depression basins, hydrocarbon generation and expulsion peaks occur in both upper thicker marine depression series of strata and lower rift series of strata. Reservoirs are formed in the structures of rift series of strata, and oil and gas are highly concentrated at slope fans in depression series of strata. In saline faulted depression basins, large oil and gas fields are mainly distributed in the lagoon carbonate rocks of subsalt series of strata and the deepwater slope fans of suprasalt depression series of strata. In saline depression basins, only petroleum systems in depression series of strata are active, and various traps are developed, such as slope fan, salt structure and bioherm. In non-saline depression basins, large oil and gas fields are mainly located in submarine fan groups of depression series of strata because this type of basins are of narrow continental shelf and steep continental slope. In delta reformed basins, four major ring-like structure belts (i.e., growth faulting-mud diapir-thrust nappe-foredeep gentle slope) are formed from the shore to the deepwater and large oil and gas fields can be formed in each belt. Positive reverse reformed basins are the passive continental margin basins which are influenced by global orogenesis since the Miocene. In this type of basins, oil and gas are concentrated in compressional anticlines of reverse series of strata. Key words: passive continental margin, prototype basin, basin structure, basin classification, large oil and gas field, distribution rules

Based on the plate tectonic theory, and by studying seismic, geologic data and related documents, this study restored the proto-type basins and lithofacies paleogeography of East African passive margin basins in the major geological periods, and carried out analysis on the basin architecture characteristics and sedimentary filling variance. Based on the dissection of fifteen reservoirs, three hydrocarbon accumulation models were identified to find out favorable plays and the further exploration direction in this region. The East African passive continental margin basins experienced three prototype stages, Late Carboniferous-Triassic Karoo intercontinental failed rifts, Jurassic intercontinental-intracontinental rifts, and passive continental margins since the Cretaceous. The rift sequences are developed in all the basins, forming the “rift type”, “rift depression type” and “delta reconstruction type” passive continental margin basins in line with the different thicknesses of the sediment fillings during the depression period. In the “rift type” basins, the sediment thickness during the depression period was less than 3 000 m, forming “single source – structure type” hydrocarbon accumulation model, where the exploration direction will mainly focus on giant structural traps on the top of the rift sequences. In the “fault-depression type” basins, the sediment thickness during the depression period was more than 5 000 m, forming “double sources – double combinations type” hydrocarbon accumulation model, where the exploration direction will mainly focus on giant slip-collapse-debris flow deposits on the top and middle of the slope. In the “delta-reconstruction type” sediment basins, the thickness is more than 6 000 m, forming constructional delta deposits with four structural belts from onshore to offshore, unique growth faults, mud diapirs, thrust faults and fore deep gentle slope, which are named as “three sources – multi-combinations type” hydrocarbon accumulation model, and all the four structural belts can form giant oil and gas fields. Key words: east Africa, passive continental margin basin, proto-type basin, lithofacies paleogeography, basin structural architecture, hydrocarbon accumulation model, deep-water sediment, petroleum exploration direction