Abstract: Through analysis on the history of hydrocarbongeneration from source rocks, paleo-structural evolution features and gas reservoir-forming composition, period of time, and gas reservoir types, it is regarded that the northeastern Ordos Basin is different from the middle and the south for their different thermal evolution degrees of organic burials of gas source rocks. Influenced by multi-stage structural uplift, gas migration, accumulation, and reservoir formation in the northeastern Ordos Basin experience two stages, that is, the early stage and the late stage. The reservoirs formed at the early stage are mainly concentrated in the south of the studied area and feature in near-sources formation under high temperature and high pressure. At the late stage, owing to the intense structural movement and the lost of abnormal pressure of regional sealing beds, gas migrates and accumulates upward and the cross reservoir-forming composition is developed. Therefore, according to the features of reservoir temperature and pressure and the process of reservoir formation, the gas reservoir-forming pattern of the area is summarized as three stages, that is, the high temperature and high pressure stage, the high temperature and low pressure stage, and the adjustment stage of temperature and pressure. On the basis of this, controlling factors and distribution laws of gas reservoirs are discussed, indicating a direction for Paleozoic gas exploration in the area.

Key words: northeastern Ordos basin, Paleozoic, natural gas, reservoir-forming pattern, the law of gas reservoir distribution