Summary of Formation Rule for Low Permeability Lithologic Reservoir of Mesozoic in Ordos Basin

Key words: 
• Ordos Basin /
• low permeability lithologic reservoir /
• hydrocarbon accumulation period /
• petroleum accumulation force /
• carrier system /
• Mesozoic

Abstract: :Ordos Basin is the typical inland depression lake basin of Mesozoic. Yanchang Formation of Upper Triassic and Yan'an Formation of Jurassic are the main oilbearing strata. Chang 7 high quality source rocks are the principal source rocks of Mesozoic oil reservoir, abnormal high pressure is the principal migration force of Mesozoic low permeability reservoir, porosity sandstone and fracture system are the main migration pathway of mesozoic hydrocarbon, the effective combination of several carrier
 system and abnormal high pressure controlled the reservoir distribution. By using the methods of the diagenetic fluid inclusion of reservoirs, authigenic illite dating and bitumen with different periods, analysis of  the petroleum accumulation period, considered that the formation of Mesozoic oil reservoir is oil migration and accumulation. The accumulation poriod can be divided into early stage, middle stage and late stage, respectively corresponded to early period, middle period and late period of early cretaceous, The main accumulation stage is the middle stage of accumulation poriod in  middle period of early Cretaceous. The formation rule for low permeability lithologic reservoir of Mesozoic in Ordos Basin has been summrized. Under the effect of abnormal high pressure which was generated by low compaction and hydrocarbongenerating pressurization of Chang 7 source rocks, hydrocarbon migrated up and down by overlying high permeability sandstone, formed largescale lithologic reservoir in Chang 4+5, Chang 6 and Chang 8, and by the passage system of micro fracture and anterior Jurassic paleoriver sand, formed structural lithologic reservoir in Chang 2 and Jurassic reservoir.