Abstract: In the First Member of Qingshuihe Formation (Qing 1 Member) in Shinan area, the Junggar Basin, sandstones and glutenites are widely developed with complex diagenesis, which is an important factor affecting reservoir development. Based on analysis of thin sections, cast thin sections, scanning electron microscope (SEM) and X-ray diffraction (XRD), together with core observation, physical property data and log data, the diagenetic characteristics of the Qing 1 Member reservoirs were studied and the differences of diagenetic characteristics between sandstone and glutenite reservoirs were analyzed. It is shown that the Qing 1 Member reservoirs experienced three diagenesis, i.e., compaction, cementation and dissolution, and they were mainly at Period B of early diagenesis and locally at Period A of middle diagenesis. Compaction is the major factor leading to the physical property loss of Qing 1 Member sandstone reservoirs. In glutenites, however, compaction was relatively weak due to the support of rigid gravels, so a large amount of diagenetic fluids flowed through its primary pores and were cemented in a large area. Therefore, cementation is the main factor affecting the physical properties of glutenites. Dissolution is an important factor for the improvement of reservoirs. In sandstone reservoirs, intragranular dissolved pores are produced by the dissolution of plagioclase grains. And in glutenite reservoirs, intergranular dissolved pores and residual intergranular pores are formed by the dissolution of calcite cement. Dissolution fluid is the acidic fluid generated during the maturation of the Permian source rocks. Five types of diagenetic facies are identified in the Qing 1 Member reservoirs in Shinan area, including strong compaction facies, strong cementation facies, mediumstrong compaction and medium cementation facies, medium compaction and weak cementation facies, and medium-strong compaction and weak dissolution facies. The medium-strong compaction and medium cementation facies is predominant. In this area, favorable reservoirs may exist in the channel sandstones of medium compaction and weak cementation facies at the structural highs (e.g. Xiayan 8 well block) and the glutenites of medium-strong compaction and weak dissolution facies in fault development zones (e.g. Shixi 12, Shinan 44 and Shinan 31 well blocks).

Key words: Junggar Basin, Shinan area, Qingshuihe Formation, diagenesis, diagenetic facies, petroleum significance