Abstract:

According to the critical condition of reservoir and caprocks, the article makes use of the evolution curves of caprock entry pressure and reservoir porosity to fix the forming depth of the lithologic traps, and at the same time proves that the lithologic traps can form in several formations. If the entry pressure of caprocks and reservoir characters regularly evolute in accordance with the nowadays evolution curve, we can deduce that lithologic traps can form in early time and the traps have several forming periods.The realistic data of Erlian Basin prove that lithologic traps have the characteristics of early and multi-period formations. The study of combining the forming times and the history of hydrocarbon migration and accumulation is important for the research on forming of lithologic traps.

Key words: entry pressure of caprock, critical properties of reservoir, early origin, multi-period formation