Sandstone reservoirs of the Jiufutang Formation are submarine fan deposits which could be divided into middle and outer fans. The submArine fans underwent three evolution stages such as development

maturation and decline stages that correspond to Ⅲ

Ⅱ and Ⅰ sand formations

and these sand formations

in turn

equal to outer fan

the outer marginal blade and the inner marginal channel of the mid-fan. The porosity of the reservoir did not change much but its permeability varied intensely. This reveals serious heterogeneity of the sandbodies.According to the capillary pressure

the reservoirs could be divided into mid pore-mid permeability

mid pore-low permeability and mid pore-very low permeability types.