The sequence controlling feature and its impact on gas injection development of low- permeability layers of Donghe1 reservoir in Tarim Basin

Logging data and core analysis show that the Donghe sandstone of Donghe1 reservoir in Tarim Basin consists of foreshore, upper shoreface and lower shoreface facies zone from the bottom upward, and can be further divided into 11 parasequences. Accord?ing to petrographic analysis, the low-permeability layers in this sandstone can be classified into three categories:calcareous cementa?tion low-permeability layers, matrix low-permeability layers and mixed low-permeability layers. The calcareous cementation low-permeability layers are cemented by calcite, siderite, and ferrodolomite mainly distributed within the parasequences and are controlled by diagenesis. The distribution of matrix low-permeability layers are characterized by the lag deposits during transgression, and are controlled by parasequence boundaries. There are a number of mixed low-permeability layers distributed either in the parasequences or along the sequence boundaries, within which the intergranular pores are filled with both matrix and calcite cements. In combina?tion with the pressure data, the parasequence boundary-controlled matrix low-permeability layers extend widely and have obvious impact on gas-injection.