Abstract: Xiakou fault is a Class-II fault with succession movement, by which Huimin 8ag can be divided into Linnan subsag and Linnan slope. Linnan oilfield and Qudi oilfield are distributed in sections near Xialou fault. The former is situated in footwall of west section of the fault, while the latter in upper wall of east section of it. Such a framework is related to the lateral differences of seal of the fault, especially to the fault occurrence. Since the west section has more seal capacity, the east section becomes the favorable pathway for petroleum migration from Linnan subsag toward Qudi area, where the steep part of the fault plays the role of preferred pathway. The steep and convex fault plane controls the petroleum migrating across the plane by the form of spreading or confluence flowing. The direction of confluence flowing is good for petroleum accumulation.

Key words: Huimin sag, fault, petroleum migration, slope