Diagenesis types and characteristics of Xishanyao Formation in Malang Sag, Santanghu Basin

There are many large-scale sandstone reservoirs in the Xishanyao Formation of the Malang Sag, Santanghu Basin, with great potential for oil and gas development. The diagenesis types and stages of the reservoir were studied by means of thin section observation, scanning electron microscopy, X-ray diffraction, vitrinite reflectance, etc. Based on this, the influence of diagenesis on the reservoir was analyzed. Eight types of diagenesis were developed in the sandstone reservoirs of the Xishanyao Formation in the study area. Constructive effects include rim chlorite cementation, alteration, dissolution and rupture, while the main destructive diagenesis includes compaction, pressure solution, and siliceous and carbonate cementation. In addition, the cementation and metasomatism will change from constructive to destructive with the backward transition of the diagenetic stage. The sandstones of the Xishanyao Formation in the study area are mainly in the late part of the middle diagenetic A stage. Compaction is the main reason for porosity reduction, while kaolinite and dissolution are the main causes for porosity increase. Chlorite rim cementation developed. The sandstones with remaining primary intergranular pores and dissolution pores are the most favorable reservoirs.