四川盆地上三叠统须家河组致密砂岩成储机制OA

The Upper Triassic Xujiahe Formation in the Sichuan Basin hosts one of China's most important tight sandstone gas reservoirs.To clarify the reservoir development mechanism under a multi-provenance framework,reservoir characteristics and the principal controlling factors associated with four major provenance systems-the Jiangnan Old Land,the Micangshan-Dabashan Fold Belt,the Kangdian Old Land,and the Longmenshan Thrust Belt-were systematically compared across the entire basin using core observations,thin-section petrography,X-ray diffraction(XRD),and high-pressure mercury intrusion(HPMI)analyses.Based on these results,the development pattern of high-quality reservoirs was established.Reservoirs sourced from different provenance systems exhibit significant differences in lithic composition and compositional maturity.The 2nd member of the Xujiahe Formation(Xu 2 Member)is dominated by lithic sandstone,whereas carbonate lithic fragments become more abundant in the 3rd member(Xu 3 Member).The 4th member(Xu 4 Member)exhibits the most favorable reser-voir properties.The reservoirs are generally characterized by ultra-low porosity(average 6.0％-10.8％)and ultra-low to extremely low permeability(average(0.005-2.238)× 10-3 μm2).Reservoir space is dominated by secondary dissolution pores,with primary pores occurring as a subordinate component.Specifically,the Xu 4 Member exhibits the optimal pore-throat structure,whereas the southeastern Sichuan provenance area displays the highest mercury withdrawal efficiency(average 38.57％)and the best pore-throat connectivity.Compaction is the primary destructive diagenetic process,followed by cementation(characterized by siliceous and calcareous cements);conversely,dissolution(specifically of feldspar and lithics)effectively improves the pore space.Com-paction is strongest in the northwestern Sichuan provenance area,while dissolution is most developed in the southeastern Sichuan provenance area.The development of high-quality reservoirs is synergistically controlled by four factors:provenance systems providing the geological foundation,sedimentary microfacies determining reser-voir quality,differential diagenesis controlling pore evolution,and fractures enhancing reservoir connectivity.Distributary channel sand bodies within braided river deltas exhibit the best physical properties,and fractures development significantly enhances the reservoir permeability in the study area.This study provides a theoretical foundation for sweet-spot optimization and the efficient exploration and development of tight sandstone gas reser-voirs within the Xujiahe Formation in the Sichuan Basin.