Sedimentary Micro-facies And Reservoir Characteristics Of The Chang 8 Reservoir Formation In The Z423-M31 Well Area

This paper takes the Chang 8 reservoir in the Z423-M31 well area as the research object.Closely combined with the actual situation in exploration and development,it is guided by multidisciplinary geological theory and methodologies such as sedimentology,reservoir geology and petroleum geology.Based on the systematic analysis of sedimentary facies markers such as petrology,sedimentary structure,grain size characteristics and logging curves,combined with the characteristics of reservoir diagenesis,heterogeneity,reservoir geology and physical properties,the main factors affecting the quality of Chang 8 reservoir in this area are determined by using the data of core,thin section,analytical test,well logging and mud logging.The main findings are as follows:The Chang 8 reservoir group in the study area is a delta-lake sedimentary system with three types of sub-facies,with delta front as the main sub-facies.There are seven types of microfacies,with underwater distributary channel,distal bar,distributary channel flank and interdistributary bay as the main microfacies.The main diagenesis types are compaction,cementation and dissolution,and the sandstone of Chang 8 reservoir in this area is in stage A of middle diagenetic phase.Reservoir sandstone is mainly fine-ultrafine feldspar sandstones,with feldspar dissolved pore as the main pore type,followed by residual intergranular pore.Reservoir belongs to ultra-low porosity and ultra-low permeability reservoir,in which micro-fractures are mainly structural fractures.Generally speaking,the quality of Chang 8 sandstone reservoir in the study area is mainly controlled by sedimentary factors and diagenesis.The study of sedimentary microfacies and reservoir characteristics of Chang 8 reservoir group in Z423-M31 well area can provide theoretical basis for reservoir description in this area or adjacent area.