The Xiaoerbulak Formation consists mainly of dark gray silt and finesized crystalline dolostones with dissolution porosity of different types and values. Highlydeveloped beddingparallel dissolution pores within the top of the Formation may have high storage capacity. Based on field and microscopic observations as well as EPMA and SEM analysis

the authors suggest that dolostone dissolution in the area features in multiperiod developments and diversified dissolution fluids. The dolostone dissolutions can be classified into four types: beddingparallel dissolution

dolostone porefilling redissolution

intergrain dissolution and hypergene dissolution. Beddingparallel dissolution occurs mainly along the bedding. The diameters of dissolution pores are about a few millimeters and most of the pores are lined with dolomite. Compared with matrix dolomite

the porefilling dolomite is richer in such elements as Fe

Mn

Na and Ba

indicating its close relationship with deep thermal fluid. Some porefilling dolomite may redissolve and reprecipitate—a process that could alter the existing pores. The precipitates are rich in S

Si

Sr and other elements

indicating a dissolution fluid with complicated compositions and diversified sources. In addition

dissolution of grain dolostone also occurs and shows the characteristics of hypergene dissolution in some places

which may contribute to the development of reservoir space.