Abstract:

Abstract: 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.