The influence of sandstone diagenesis on reservoir of Shaximiao Formation in southwest Sichuan

Jurassic Shaximiao Formation is an important tight gas reservoir in southwest Sichuan. In this study, thin section identification, scanning electron microscopy (SEM), X-ray diffraction (XRD), Cathodolumines- cence(CL), electron probe analysis, fluid inclusions and isotopic analysis were used to investigate the characteristics of the reservoir and the influence of diagenesis on the reservoir. And the following research results are obtained.First, the reservoir rock types of Shaximiao Formation in this area are primarily feldspathic sandstone and lithic feldspathic sandstone and secondarily lithic sandstone and feldspathic lithic sandstone. Second, the reservoir performance of feldspathic sandstones is much better than that of lithic sandstones. Feldspathic sandstones are mainly vertically distributed in the first and second sub-members of the second Member of Shaximiao Formation and laterally the most developed in the eastern area.Third, the reservoir Spaces in southwest Sichuan are mainly primary intergranular pores and secondary intergranular pores. Compaction plays a dominant role in the reduction of porosity, and due to the protective effect of chlorite coating, the porosity in southwest Sichuan is reduced by 23.45%. Cementation played a secondary role in the reduction of porosity, which reduced the porosity of southwest Sichuan by 12.4% respectively. On the contrary, dissolution plays a positive role in the increase of porosity, which increases the porosity of southwest Sichuan by 4.52%.In conclusion, Compaction and cementation lead to reservoir densification in Shaximiaoformation. Chlorite cementation protects the primary porosity to a certain extent, and dissolution is the main factor to increase the porosity.