Abstract:

The result from the experimental analyses of the 3rd member of Shahejie Fm (Es₃) 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 Es₃⁴ has the biggest breakthrough pressure, then the Es₃² comes next, and the Es₃³ 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.

Key words: claystone caprock, reservoir quality, sealing capacity, breakthrough pressure, evaluation standard, Dongpu depression.