Quantitative classification of diagenetic facies in tight sandstone gas reservoirs based on multi-parameter evaluation: A case study of the first member of Shanxi Formation in the Shenmu Gas Field,Ordos Basin

Diagenesis types, intensity and facies were evaluated using a variety of laboratoryresults and logging data in order to explore the quantitative classification method of diagenetic facies in tight sandstone gas reservoirs. Diagenetic facies classification standardswere established based on diagenesis and logging parameters. The basic characteristics of different diagenetic facies were elaborated taking the first member of Shanxi Formation in the Shenmu Gas Field in the Ordos Basin as an example.Dissolved pores, intercrystalline pores and small amounts of intergranular pores developed in the first member of Shanxi Formation in the study area. The formation is characterizedby medium compaction (locally weak or strong compaction), medium cementation (locally weak or strong cementation), and medium to strong dissolution. Five diagenetic facies weredefinedaccording to diagenesis intensity, cementation and pore types.Furthermore, diagenetic facies could be effectively recognized based on natural gamma ray logging, deep lateral resistivity logging, density logging and acoustic logging.The distribution of favorable diagenetic facies was controlled by advantageous sedimentary microfacies. Obvious differences appear among different diagenetic facies. Moderate compaction illite, dissolution pore+intergranular pore facies with eitherchloriteor kaolinite cementation, distributed in distributary channel microfacies of delta plains are favorable diagenetic facies in the study area.