Abstract: The presence of episode compaction/fracturing phenomena of mud rocks and the discovery of boiling fluid inclusions in the sand lens show that the episodic charge mechanism of the overpressure fluids is a predominating cause for the reservoir formation. Based on the migration/accumulation dynamics and mode, on the type of conduit framework and mode of fluid flow and on the formation characteristics, migration/accumulation mechanism and the reservoir formation model, the dynamic types of sand lens reservoirs formation are classified into capillaryoverpressure control and single overpressure control types. The mode of fluid flow is discussed. It is believed that there may be both lateral and vertical flows in the sand lens under the overpressure condition.

Key words: sand lens, overpressure, accumulation dynamics, episode accumulation