Diagenesis of reservoir rocks of the lower Jurassic and its influence on porosity modification in North Qaidam Basin

The reservoir rocks are mainly composed of sublitharenite and litharenite.The main diagenesis includes compaction,cementation,dissolution,replacement and recrystaUization.Compaction and cemen- tation of carbonate led to great decreas in eoriginal pores.Dissolution of feldspar created considerable secondary pores.Contents of smectite,illite,kaolinite,chlorite,mixed-layered illite/smectite are changeable in a wide range.The contents of mixed-layered chlorite/smectite are extremely low.Vitrinite reflectance ranges from 0.33% to 1.47% for the overwhelming majority of samples.The rocks evolved at the late phrase of late diagenesis,and some reservoir rocks experienced epidiagenesis.