Abstract: The distribution of fluid residual pressure of Mesozoic strata in Ordos basin is studied based on the equilibrium depth method. The residual pressure presented in each well of the studied area is mostly distributed in Chang-7, followed by Chang-6, Chang-4+5 and Chang-8 in turn. The study shows that most oil fields are found in plane in the low-value belt of residual pressure of the corresponding oil layers, and vertically in the relative low-value belt of abnormal pressure segments as well as the normal pressure ones, by which the oilgas migration and accumulation conditions of Chang-7 layer are analyzed. It is pointed out that Ansai and Yanchi are the oil accumulated areas of Chang-2, the east of Longdong-Baibao-Jingbian is the target area of Chang-6 oil migration and enrichment, while Longdong, Baibao and Jingbian are the target areas of Chang-8 oil migration and enrichment.

Key words: Ordos basin, Triassic, residual pressure, oil migration, oil accumulation, sonic logging