Relationship between Unconformity and Hydrocarbon Accumulation in the Eastern Qaidam Basin

This study discussed the relationship between unconformity type and oil trap,and unconformity structural type and oil-gas migration-accumulation,and the hydrocarbon-forming pattern of unconformity migration-accumulation in eastern Qaidam Basin.The Qaidam Basin has undergone multistage tectonic movements and formed several unconformities.The unconformities of the eastern Qaidam Basin can be divided into drape unconformity,fault-fold unconformity,truncation unconformity,onlap unconformity and parallel unconformity in terms of the function of unconformity migration-accumulation and their forming mechanisms as well as reflection characters in seismic sections.They are of typical stratiform structure due to uneven weathering and eroding processes,including overlying rocks above the unconformity interface,such as weathered clay and semi-weathered leached zone.Vertical stratiform structure of unconformities provides not only dual pathways for oil and gas migration,but also accommodation space for oil and gas accumulation.It was the position and diversity of unconformity developed that resulted in different models of oil and gas reservoir formation under various settings of unconformity.