Abstract: The Chang-3 sandstone reservoirs from the Hua-152 block in the Huachi Oil Field mostly consist of fine-grained feldspar sandstone and lithic sandstone in which various pore types are developed,including intergranular solution openings,intragranular solution openings,residual intergranular pores,intercrystal micropores and structural fissures.The intergranular solution openings occur as main pore types in the study area.The major diagenetic minerals include illite,chlorite,mixed illite-smectite,gaolinite,calcite,dolomite and quartz overgrowths.According to mineral indicators for diagenesis,the Chang-3 sandstone reservoirs in the study area are interpreted to be in the stage A of middle diagenesis.The compaction and cementation are responsible for the destruction of the primary pore structures of the sandstones,whereas the dissolution of feldspar and lithic fragments resulted in the development of secondary pores and improvement of the pore structures of the sandstones.