Study on the Lithological Characteristics and Its Controlling on the Development of Specific Tight Sandstone Reservoirs

Diagenesis is a series of physical and chemical reactions that take place after deposition. Using cores, thin sections, cathode luminescence, X-ray diffraction, scanning electron microscope, inclusions analysis, geochemical analysis and pore permeability data, the diagenesis, and its influence on the tight sandstone reservoir of Xu 2 member in the southwest Sichuan Basin has been analyzed. The reservoirs of the southwest Sichuan Basin mainly consist of feldspathic feldspathic sandstone, feldspathic feldspathic sandstone, and felsic sandstone, with an average porosity of 3.57% and an average permeability of 0.138·10-3 μm2, which are typical tight sandstone reservoirs. The sandstones in the Xu2 member mainly underwent compaction, dissolution, cementation and accounting, and the specific evolution process is compaction , first-phase fracture, first-phase quartz increase, first-phase calcite cementation, second-phase fracture, feldspar and rock chip dissolution, second-phase quartz increase and silica filling, chlorite cementation or illite cementation, second-phase calcite cementation, dissolution, third-phase quartz increase and silica filling, the third stage of carbonate cementation, carbonate accounting for feldspar and quartz- third stage of tectonic fragmentation, late calcite or quartz cementation into rocks. And the rock formation stage is mainly mesodiagenesis B stage. The secondary pores and microfractures are the main reservoir space in the Xu 2 member sandstone reservoirs. Strong compaction and carbonate cementation are the main reasons for the tight sandstone reservoir, and dissolution and fracture are the main constructional effects for the development of the dominant reservoir.