Laterally

the Tertiary unconformity reservoirs of the Jiyang depression are mainly distributed in the large nosing structures of the marginal overlap zones and the flanks of salients

while vertically

they occur mainly near the first-order unconformity surface.Three types of structures

namely the type Ⅰ

Ⅱ

and Ⅲ

are identified in the Tertiary unconformity surface according to the degree of weathering and preservation of strata both above and below the surface.Different types of structures vary in conductivity/sealing ability.The main factors that control hydrocarbon accumulation in the Tertiary unconformity reservoirs are palaeogeomorphology

conducting systems and barrier beds.Two patterns of hydrocarbon migration and accumulation

namely forward direction pat-tern on slope and sideway pattern on salient

are established through observation of structural location of uncon-formity traps

occurrence of reservoirs

and migration direction of hydrocarbons.Both of the patterns are favorable for development of proximal sealed reservoirs and distal overlap reservoirs

with the"conducting hatch"in un-conformity body acting as the transition between these two kinds of reservoirs.