Diagenesis of Paleogene-Neogene sandstone reservoirs in Lenghu-Maxian area,northern Qaidam Basin

Based on cores,cast thin sections,scanning electron microscope and testing data,this paper studied the diagenesis of Paleogene-Neogene sandstone reservoirs and its influence on reservoir properties in Lenghu-Maxian area in north Qaidam Basin.The result shows that the sandstone reservoirs in this area are mainly composed of lithic arkose,arkose and feldspar lithic sandstone,and mainly experienced such actions as compaction,cementation and dissolution.Mechanical compaction is the main compaction,cementations are mainly carbonate cementation,sulfate cementation,quartz overgrowth and clay minerals cementation,and dissolution comprises carbonate cementation content and detrital dissolution.Compaction and cementation caused the destruction of primary pores and made the reservoir properties poor.Dissolution of the lithic and cement was the main reason for generating secondary pores.According to the characteristics of vitrinite reflectance and clay minerals,it is ascertained that the evolution have reached the early diagenetic stage A,and the minor part reached the middle diagenetic stage B.