四川盆地天府地区上三叠统须家河组四段致密砂岩气藏地质甜点评价OA

Taking the tight sandstone reservoirs of the fourth member of the Upper Triassic Xujiahe Formation(T3x4)in the Tianfu area of the Sichuan Basin as the research object,the study systematically analyzed the controlling effects of sedimentary processes,diagenesis,and source fault-fracture system on gas reservoirs.Evaluation criteria were established for evaluating geological sweet spots of tight sandstone gas reservoirs in this region.The results showed that:(1)The lithology of the T3x4 sandstone reservoirs was mainly feldspar lithic sandstone,followed by lithic sandstone.Grain size was mainly medium sand.Porosity was mainly distributed between 6%and 8%,and permeability was mainly in the range of(0.1-0.5)×10-3 μm2,representing ultra-low porosity and ultra-low per-meability porous reservoirs.(2)The physical properties of the reservoirs were jointly controlled by sedimentary processes and diagenesis.Delta front sand bodies exhibited better sorting and lower clay content,resulting in superior reservoir properties and pore structure than delta plain sand bodies.Mechanical compaction was the primary cause of reservoir densification,followed by calcite cementation and illite filling.Chlorite films effectively pre-served primary pores and played a constructive role in maintaining pore structure.(3)Based on reservoir physi-cal properties,gas-bearing characteristics,and fracture development features,the T3 x4 reservoirs were divided into three types of geological sweet spots.Type I sweet spots were characterized by relatively high porosity with developed fractures(porosity＞8%,fracture density≥1 fracture/m).Type Ⅱ sweet spots were high-porosity zones(porosity＞8%,fracture density＜1 fracture/m)or relatively high-porosity intervals with developed frac-tures(porosity 6%-8%,fracture density≥1 fracture/m).Type Ⅲ sweet spots were relatively high-porosity zones without fractures(porosity 6%-8%,fracture density＜1 fracture/m)or low porosity intervals with developed fractures(porosity＜6%,fracture density≥1 fracture/m).