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This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny (Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55–94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170–196 m and 11 298 kmbrespectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle–Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma4 Member–pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.

Based on field outcrop investigation, interpretation and analysis of drilling and seismic data, and consulting on a large number of previous research results, the characteristics of ancient marine hydrocarbon source rocks, favorable reservoir facies belts, hydrocarbon migration direction and reservoir-forming law in the Ordos Basin have been studied from the viewpoints of North China Craton breakup and Qilian-Qinling oceanic basin opening and closing. Four main results are obtained: (1) Controlled by deep-water shelf-rift, there are three suites of source rocks in the Ordos Basin and its periphery: Mesoproterozoic, Lower Cambrian and Middle-Upper Ordovician. (2) Controlled by littoral environment, paleo-uplift and platform margin, four types of reservoirs are developed in the area: Mesoproterozoic– Lower Cambrian littoral shallow sea quartz sandstone, Middle-Upper Cambrian–Ordovician weathering crust and dolomitized reservoir, and Ordovician L-shape platform margin reef and beach bodies. (3) Reservoir-forming assemblages vary greatly in the study area, with “upper generation and lower storage” as the main pattern in the platform, followed by “self-generation and self-storage”. There are both “upper generation and lower storage” and “self-generation and self-storage” in the platform margin zone. In addition, in the case of communication between deep-large faults and the Changchengian system paleo-rift trough, there may also exist a “lower generation and upper reservoir” combination between the platform and the margin. (4) There are four new exploration fields including Qingyang paleo-uplift pre-Carboniferous weathering crust, L-shape platform margin zone in southwestern margin of the basin, Ordovician subsalt assemblage in central and eastern parts of the basin, and Mesoproterozoic–Cambrian. Among them, pre-Carboniferous weathering crust and L-shape platform margin facies zone are more realistic replacement areas, and Ordovician subsalt assemblage and the Proterozoic-Cambrian have certain potential and are worth exploring. Key words: natural gas exploration area, hydrocarbon accumulation geological conditions, Mesoproterozoic, Neoproterozoic, Lower Paleozoic, Ordos Basin

The control of structural evolution on the development of different types of Ordovician reservoirs in the Ordos Basin is discussed by studying the evolution of the Ordovician top boundary in geological times, and the mechanisms of formation and evolution of carbonate reservoirs are examined. The top boundary of the Ordovician is an important sequence boundary in the Ordos Basin. It represents not only the depositional change between lower marine carbonate rocks and upper clastic rocks, but also a depositional break caused by weathering and corrosion from the Late Calidonian to the Early Hercynian. It experienced three great structural changes in the geological history, which influenced the formation and conservation of the Ordovician reservoirs. Difference of lithology of the Ordovician top sequence between the east and west of the basin controlled the type of reservoir space and caused the formation of different reservoirs of corrosive pores. However, the later reversal of the sequence boundary causes the filling of early formed pore space in the eastern basin, and affects the space distribution of effective reservoirs. Key words: Ordos Basin, Ordovician, reservoir, sequence stratigraphy, sequence boundary, pore filling