Carboniferous Donghe Sadstone in Tazhong 4 Oilfield can be divided into two sub-members, i.e. equigranular sandstone in lower part and pebbly sandstone in theupper. The upper sub-member can be further divided into four sandstone units interlayered with 4 argillite units. Almost all oil and gas reservoirs are found in the upper sub-member. The pebbly sandstone sub-member is characterized by stable, widely distributed near-shore sediments in general, with the main sandbody elongated in the NW-SE direction, parallel to shoreline. Sedimentary faciesof the sandstone units is dominated by the beach of former shore face and uppershore face. The argillaceous interlayers were formed in the blow shore face environment, and played a role as caprock for the oil gas store in the rim area. Reservoirs in the pebbly sandstone submember are composed mainly of quartzosesandstone, and subordinate litharenite. The storage space is dominated by relict primary intergranular pores, some of them can also be results of late dissol ution. Majority of the reservoirs are valued as Grade II and Garde III with mediate (low) porosity and mediate (low) permeability, with some valued as Grade I.

