The Types And Forming Mechanism Of Petroleum Reserviors In Mesozoic, North Shanxi Slope, Ordos Basin

Mesozoic oil and gas reserviors in Ordos Basin mainly distributed in Yanchang Formation of Late Triassic and Yan'an Formation of Early Jurassic, more than 90% of petroleum reserviors of the basin gathered in North ShanXi Slope. Oil and gas originate from lake-facies sedimentary system of Yanchang Formation.Influenced by sedimentary facies, structure and migration, types of Mesozoic oil reserviors in North of Shanxi Slope is various. In general,Chang8,Chang7,Chang6,Chang4+5 oil reservoir of Yanchang Formation are mainly lithologic, while Chang2,Chang3 and Jurassic oil reservoirs are lithologic-structural, some parts have different characteristics because of different geologic condition. Yanchang Formation of Huachi oil field developed a series of deep lake-meare-delta facies sedimentation, oil reservoirs mainly gathered in delta facies sedimentary system of Chang3 section, and was little influenced by structure, mainly lithologic and lithologic-structural; lower part of Yan'an Formation developed a series of braided stream- meandering stream delta facies sedimentation, oil reservoirs mainly gathered in Yan10 section and clearly influenced by structure, are structural or lithologic-structural; topographic irregularity of Yan8 and Yan9 section are very small, mainly receive delta front facies sedimentation, gradually influenced by lithologic change, mainly developed lithologic oil reservoirs. Chang6,Chang2 major reservoirs of Yanchang Formation in Jing'an oil field mostly distributed in large scale delta front which formed in this period, in it, Chang6,Chang4+5 oil reservoirs are lithologic or structural-lithologic; Chang2 oil reservoir is mainly structural-lithologic; Jurassic oil reservoirs are mostly structural-lithologic. In conclusion, from lower to upper part of Yanchang Formation, structure control on oil reservoirs is strengthened gradually, and lithologic condition control is weakened; and in Yan'an Formation structure influenced Yan10 more clearly than Yan8,Yan9 oil reservoirs.Forming of oil reservoirs in Yanchang Formation mainly based on abundant hydrocarbon mother rock,perfect assemblage of container rock and cap rock,split formed by basal fault and so on, while distribution of oil reservoirs is related to delta sand body> basal active belt and blister. Forming of Jurassic oil reservoirs is closely relative to palaeochannel of Early Jurassic and oil reservoirs in Yanchang Formation which next to palaeochannel, distribution of Jurassic oil reservoirs mainly concentrated in compact structures and rise of underlying strata.