A big oilfield could be formed by a trap with the upper equilibrium structure preserving petroleum and the lower dissipated structure injected with oil and gas continuously.

• 油气圈闭要同时具备平衡结构和耗散结构，上部为平衡结构，使油气得以保存；下部为耗散结构，使油气不断充注，形成大的油气田。