Diagenetic differences controlled by sediment composition and their implications for reservoir quality in the deep-buried Permian Urho Formation,Fukang Sag,Junggar basinOA

Deeply buried coarse clastic reservoirs of the Permian Upper Urho Formation in the Fukang Sag,Junggar Basin,exhibit pronounced reservoir-quality heterogeneity in pore systems and lithofacies architecture.However,how provenance-controlled sediment composition regulates mineral transformation and divergent diagenetic pathways,thereby controlling reservoir quality,remains unclear.This study integrates petrographic observations,XRD,SEM,MIP,EPMA,and bulk-and micro-XRF analyses to clarify the diagenetic evolution and the factors controlling reservoir quality in these deposits.The results indicate distinct provenance-controlled diagenetic pathways in two reservoir domains:(1)Reservoirs affected by the Xiquan Uplift Provenance,which contain intermediate-mafic volcanic materials,underwent stronger chemical weathering,enhanced mechanical compaction,and widespread illite-smectite mixed-layer mineral(I/S)cementation,leading to pore systems mainly composed of intercrystalline pores within clay minerals;(2)Reservoirs sourced from the Eastern Provenance,characterized by intermediate-acidic volcanic inputs,exhibit higher textural maturity and better fluid mobility,which favored the formation of early diagenetic authigenic chlorite coatings,the preservation of residual intergranular pores,and the dissolution of laumontite and feldspar;and(3)The alteration of the tuffaceous matrix differed according to diagenetic fluid chemistry.Micro-XRF elemental maps,EPMA oxide compositions,and mineral assemblage trends indicate that K-rich conditions promoted I/S enrichment,whereas Na-rich conditions favored laumontite formation followed by selective dissolution.These contrasting diagenetic pathways exert a first-order control on reservoir-quality heterogeneity.High-quality reservoirs are mainly developed in low-matrix,grain-supported thick sand bodies and sandstone interbeds within conglomerate successions,indicating that facies type,matrix content,and framework support are key screening criteria for reservoir prediction in deeply buried coarse clastic systems.