Hydrocarbon third migratgion is a periodic flow process. When faults are in dormantstage

large faults are sealed and hydrocarbons could accumulate to the fault traps within abnormal high pressure source sets to form primary pools lwhen faults are active

large faultsare open

hydrocarbons in the primary pools would migrate upward along the large faults toform secondary hydrocarbon pools in shallow traps. As the third migration is quick and concentrated

it did not result in evident chromatographic effect but did result in obvious differentiae between the primary and secondary pools since most of the hydrocarbons overflowedfrom the primary pools are light components. The hydrocarbons overflowed continuouslyfrom the primary pools

and were flushed by water-flow

then entered different reservoirswith water-flow

thus resulting in random distribution of secondary pools vertically.