Through the evaluation of macroscopic sealing parameters(lithology

mudstone accumulative thickness and single mudstone thickness) and microscopic sealing parameters(permeability and displacement pressure)

this paper gives a comprehensive analysis of the sealing capacity of the Tugulu Group in the southern margin of Junggar Basin.The results show that the Hutubi Formation is the main cap and comprises interbedded mudstone

silt mudstone and pelitic siltstone.The shale stratum ratio

average mudstone accumulative thickness and maximum single mudstone thickness are 80%-95%

337 m and 138 m respectively.Permeability and displacement pressure of the Tugulu Group mudstone range from 0.000 001 84×10

-3

μm

2

to 0.000 24×10

-3

μm

2

and 4.72 MPa to 44.85 MPa respectively

suggesting type Ⅰ to Ⅱ sealing capacity based on the criteria for cap rock evaluation.By restoring the dynamic evolution of displacement pressure of cap rocks

the Tugulu Group is capable of sealing oil and late gas generated by the Jurassic source rock

because the timing of sealing capacity forming is well in tune with the timing of hydrocarbon generation and expulsion.Uplifting and thrust faults evolved during the Hemalaya Movement did not destroy the sealing capacity of the Tugulu Group.Through these comprehensive analysis

we conclude that cap rocks of the Tugulu Group maintains the capacity of sealing large to middle gas field.