Study on the diagenesis and diagenetic facies of Chang 4+5 reservoirs in Hujianshan-Wangwazi area of Ordos Basin

The diagenesis and disgenetic facies of Chang 4+5 reservoirs in Hujianshan-Wangwazi area of Ordos Basin are systematically studied by using the analysis data of rock casting thin sections,scanning electron microscope and X-ray diffraction. The result indicates that the destructive diagenesis to reservoir mainly involves compaction,cementation and metasomatism,while the constructive diagenesis mainly involves chlorite cementation and dissolution at early stage. It is concluded that the diagenetic evolution of Chang 4+5 reservoirs has mostly been in the subphase A of the middle diagenesis,with a little in the subphase B of the middle diagenesis. Three types of diagenetic facies are demarcated for the study area,including feldspar corrosion-chlorite film cementation,kaolinite cementation,and ferrocalcite cementation. The feldspar corrosion-chlorite film cementation is the best reservoir facies,thus providing reference to further reservoir evaluation.