K-Ar dating results of authigenic illite in reservoirs indicate that charging time of gas in Bohu sag

Yanqi basin

might have roughly been divided into two phases:one is in 107.8～67.8 Ma

corresponding to Late Cretaceous;another is in 51.3～34.8 Ma

being equal to post-Eocene. Horizontally

various structures have different reservoiring stages.The reservoiring time has successively been later and later from south to north in the northern sag.The reservoiring in south and middle blocks of Baolang reservoir might have occurred in Late Cretaceous

and oil and gas have been generated in late Yanshan period;while reservoiring in north block of Baolang reservoir have occurred in Oligocene

and have been sourced from both the readjustment of primary reservoir in middle block and secondary hydrocarbon generation in Himalayan period.The reservoiring time in the southern sag might have been in later stage of Late Cretaceous.Vertically

the K-Ar dating indicates that the reservoirs in the same structural belt are younger with less buried depth

which mean that oil and gas have migrated upwards

and shallower structures have been charged from the readjustment of deeper structures.