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The Sverdrup Basin is one of the important petroliferous basins in the Arctic. It has abundant oil and gas resources, but the exploration degree is relatively low. Based on the IHS database and literatures in the public domain, this paper documented the geological characteristics and distribution of oil and gas in the Sverdrup Basin, and classified the petroleum systems and hydrocarbon plays in the basin. The undiscovered hydrocarbons were eventually assessed by Monte Carlo simulation and the favorable exploration areas were predicted. The investigation results show that the discovered oil and gas accumulations are mainly distributed in the western area of the basin, which consists of Sabin and Edinburgh sub-basins. Oil and gas are mainly reserved in the Jurassic and Triassic clastic reservoirs. Two petroleum systems, which are the Paleozoic and Mesozoic systems, were identified in the basin. The Mesozoic petroleum system has a far greater exploration potential. Undiscovered recoverable reserves (mean value) in the Mesozoic petroleum system are 474.81 MMbbl (1 MMbbl=1×106 bbl, 1 bbl=0.137 t) of oil, 13 620.82 Bcf (1 Bcf=1×109 ft3, 1 ft3=0.028 3 m3) of natural gas and 63.66 MMbbl of condensate, amounting to 2 808.61 MMboe (3.85×108 t), of which the natural gas accounts for 80.82%. The Lower Jurassic structural hydrocarbon play in the western area of the basin, the Upper Triassic-Lower Jurassic structural hydrocarbon play in the Edinburgh sub-basin and the Upper Jurassic structural hydrocarbon play in the Sabine sub-basin are the most promising exploration areas.

In recent years, primary hydrocarbon accumulations of Precambrian-Lower Cambrian have caused an increasing attention in the oil and gas explorations worldwide. The Eastern Siberian Basin in Russia, the Oman Basin in the Middle East, and the Sichuan Basin in China are endowed with the richest oil and gas reserves in the Precambrian-Lower Cambrian primary hydrocarbon accumulations. This study takes these three basins as examples to systematical and comprehensively document the geological characteristics and distribution of the global Precambrian-Lower Cambrian primary hydrocarbon accumulations through a large amount of data analysis and statistics, to provide insights for further breakthroughs of oil and gas explorations in ancient stratigraphic successions of sedimentary basins. The global proven and controlled reserves of Precambrian-Lower Cambrian primary hydrocarbon accumulations have reached 30.09×109 boe (4.12×108 t), of which 84.2% are distributed in the Eastern Siberian Basin, while the Oman Basin and the Sichuan Basin account for 8.9% and 6.5%, respectively. The source rocks are dominated by marine mudstones, shales and carbonate rocks, which are generally immature to over-mature and mostly distribute in low structural parts. Carbonate rocks and clastic rocks are important types of reservoir rocks. Early dolomitization, superficial leaching and hydrocarbons injection are important mechanisms for the development of ancient carbonate reservoirs. Most of the hydrocarbons in deep and ultra-deep ancient strata are stored in carbonate rocks. At the same time, the extensively developed high-quality regional caprocks are the key to preserving abundant hydrocarbons. Three types of accumulation models, self-generating and self-preserving, reservoirs adjacent to source rocks, and reservoirs isolated to source rocks, constitute the main models of Precambrian-Lower Cambrian primary hydrocarbon accumulations.

Systematic analyses of statistical data of shale oil resources and an integrated investigation of geological elements in major shale oil basins in USA were made. They characterize the distribution features of shale oil resources and document the controlling factors for shale oil endowment in USA. The results provide insights for shale oil exploration and production in China. Recoverable shale oil resources amount to 1 51×109 bbl in USA, of which 36.5×109 bbl have already been proven with a discovery rate of 24.2%. The shale oil resources are unevenly distributed. The Permian Basin has the lion's share of the total, followed by the Gulf and Williston basins. The enrichment of shale oil resources is largely governed by the volume of high quality source rocks, the extensive top and bottom seals of shale oil plays and the scale of "sweet spots" in shale oil reservoir intervals. The former two control the total endowment of shale oil resources and the latter controls the production volume of shale oils. It is suggested that China's shale oil exploration should focus on the selection of favorable plays and their fairways in large sedimentary basins. The delineation of new "sweet spots" and the expansion of the extent of known "sweet spots" are the keys for the new breakthroughs of shale oil exploration and the increase of both shale oil production and reserves.

The integrated analyses, classification and comparison of petroleum systems, combined with the latest oil and gas field data from the Middle East and the previous research results, indicate how tectonic-depositional evolution, source rocks and seals, and petroleum resource endowment are inter-linked. The impacts of these factors on the enrichment of petroleum resources could be established. There are four super petroleum systems in the passive margin basins of the Arabian Plate, namely, the intra-craton, the back-arc, the passive margin and the active margin, among which the passive margin and intra-craton super petroleum systems are the most significant. Regionally, oil and gas in the study area are mainly concentrated in the Central Arabian Basin and the Rub' Al Khali Basin. Stratigraphically, oil is mainly reservoired in the Cretaceous and Jurassic whereas the gas in the Permian and Triassic. The diffe-rential enrichment of hydrocarbons is mainly controlled by three factors: the distribution of high-quality effective source rocks and the positive structural trends of basins, which have a dominant control on the regional distribution of oil and gas, and the regional seals, which govern the stratigraphic distribution of oil and gas.

In order to reveal the development mechanism of high-quality clastic rock reservoir, the basic characteristics of Sha-3 Member of the Shahejie Formation in the Raoyang sag, Bohai Bay Basin, are analyzed based on cores observation, thin-sections and SEM images, and petrophysical properties measurements as well. It is found that high-mature composition and texture, early oil charging, and dissolution are the main factors controlling the formation and preservation of pores in deep reservoirs. Compaction is the major factor destructing pores, whereas formation overpressure is conducive to the preservation of original pores, high compositional and medium textural maturity can enhance the resistance capacity to compaction and protect primary pores. Early oil charging could lead to temporary cessation of diagenesis and thus inhibit the cementation. When organic acids entered reservoir formations, considerable amounts of secondary pores were formed, leading to the local improvement of petrophysical properties. When predicting good quality belt in exploration of deep basin, it is recommended that the superimposing effects of the multiple factors (overpressure, early oil charging, compositional and textural maturity, diagenesis) be taken into consideration. Key words: Bohai Bay Basin, Raoyang sag, rifted basin, Shahejie Formation, diagenesis, high porosity zone, dissolution

The Proterozoic–Lower Paleozoic marine facies successions are developed in more than 20 basins with low exploration degree in the world. Some large-scale carbonate oil and gas fields have been found in the oldest succession in the Tarim Basin, Ordos Basin, Sichuan Basin, Permian Basin, Williston Basin, Michigan Basin, East Siberia Basin, and the Oman Basin. In order to reveal the hydrocarbon enrichment roles in the oldest succession, basin formation and evolution, hydrocarbon accumulation elements, and processes in the eight major basins are studied comparatively. The Williston Basin and Michigan Basin remained as stable cratonic basins after formation in the early Paleozoic, while the others developed into superimposed basins undergone multistage tectonic movements. The eight basins were mainly carbonate deposits in the Proterozoic–early Paleozoic having different sizes, frequent uplift, and subsidence leading to several regional unconformities. The main source rock is shale with total organic carbon content of generally greater than 1% and type I/II organic matters. Various types of reservoirs, such as karst reservoir, dolomite reservoir, reef-beach body reservoirs are developed. The reservoir spaces are mainly intergranular pore, intercrystalline pore, dissolved pore, and fracture. The reservoirs are highly heterogeneous with physical property changing greatly and consist mainly of gypsum-salt and shale cap rocks. The trap types can be divided into structural, stratigraphic, lithological, and complex types. The oil and gas reservoir types are classified according to trap types where the structural reservoirs are mostly developed. Many sets of source rocks are developed in these basins and experienced multistage hydrocarbon generation and expulsion processes. In different basins, the hydrocarbon accumulation processes are different and can be classified into two types, one is the process through multistage hydrocarbon accumulation with multistage adjustment and the other is the process through early hydrocarbon accumulation and late preservation.