Study on the diagenetic facies characteristics of Chang 6 reservoir of the Upper Triassic Yanchang formation in Jiyuan area

Based on the study on casting thin sections and scanning electron microscope,this paper discusses the diagenesis and diagenetic facies of Chang 6 interval of Upper Triassic in Jiyuan area.Research shows that Chang 6 interval has poor physical properties,mainly consisting of fine debris-feldspar sandstone and feldspar sandstone with low component maturity and middle structure maturity.Reservoir is in the A-B period of diagenetic stage,primary pore decreasing by compaction,calcite and siliceous cementation not only destroying primary pore but also lowering secondary pore,rim cementation of chlorite effectively preserving primary pore and the later dissolution to some extent improving reservoir physical property.According to the diagenesis effect on reservoir,it marks off four diagenetic facies related to corresponding sedimentary facies:chlorite rim residual hole facies related to underwater distributive river course sands,biotite compaction facies related to margin of underwater distributiveriver course sands and distributary interchannel,carbonate cement facies and kaolinite weakdissolution facies.