Diagenesis of tight sandstone and its influence on reservoir properties: A case study of Fuyu reservoirs in Songliao Basin, China

Diagenesis is the primary cause of the densification of the Fuyu reservoir in Sanzhao sag, Songliao Basin. In this paper, the types of diagenesis, the influence of diagenesis on reservoir physical properties and the formation reasons of tight reservoir in Fuyu oil layer were studied by means of ordinary thin sections, casting thin sections, cathodoluminescence and scanning electron microscope. Results show that the diagenesis of the Fuyu reservoir in Sanzhao sag mainly includes compaction, cementation, metasomatism, and dissolution. Compaction and cementation are the main reasons for the compactness of the Fuyu reservoir in Sanzhao sag. The compactness causes also vary in different parts of the Fuyu reservoir. At the bottom of the Fuyu oil layer, the porosity reduction rate of early calcite cementation is 77%, and that of compaction is 9.23%. Cementation is the primary cause of reservoir compactness, and compaction is the secondary factor. In the middle and upper sections of the Fuyu reservoir, the porosity reduction rate of compaction is 50%, and that of cementation is 32.31%. Compaction is the main reason causing reservoir compactness, and cementation is the secondary factor. This work extensively analyzes the diagenesis characteristics of the Fuyu reservoir and its influence on the reservoir physical properties, providing a scientific basis for the study of the reservoir physical properties and the prediction of high-quality reservoirs.