The result from the experimental analyses of the 3rd member of Shahejie Fm (Es

3

) claystone's sealing capacity in the deep gas pools in Duqiaobai area in Dongpu depression shows that the variation in porosity has been controlled by depth and horizons

whereas the permeability has close relation with depth

but it is almost not affected by the horizons

and doesn't have obvious relation with porosity and other related parameters

too. The breakthrough pressure is getting greater with the increase of depth

but this trend is not very prominent. There is a close relation between the breakthrough pressure and the horizons

among which

the Es

3

4

has the biggest breakthrough pressure

then the Es

3

2

comes next

and the Es

3

3

has relatively low breakthrough pressure.For the sake of evaluating the sealing capacity of cap rock accurately

porosity

permeability

displacement pressure

and pore diameter have been selected as the indexes of cap rock evaluation

and weight coefficients of 0.1

0.3

0.5

and 0.1 have respectively been given to them based on their importance

so as to determine the evaluation standards caprocks of deep gas pools in Dongpu depression: when the weight coefficient is larger than 0.8

the cap rock belongs to I type

with good sealing capacity; if it is in the range of 0.6～0.8

the cap rock belongs to type Ⅱ

having moderate sealing capacity; when it is in the range of 0.5～0.55

the cap rock belongs to type Ⅲ; and if it is in the range of 0.3～0.45

the cap rock belongs to type IV; when it is less than 0.3

it is then of non-caprock.