Diagenetic Facies and High Quality Reservoir Distribution of Chang 8 Sandstones in Zhenbei Area of Ordos Basin

The characteristics of diagenetic facies and the distribution of high quality reservoirs of Chang 8 sandstones in Zhenbei Area of Ordos Basin were analyzed by using various testing methods,such as identification of casting thin sections,electron scanning microscope,X-ray diffraction and mercury intrusion method.The research results indicate that Chang 8 reservoirs are dominated by lithic arkose and feldspathic lithic sandstones,textural maturity and compositional maturity of sandstones are low.The Chang 8 reservoirs are characterized by low-extra-low porosity and extra-low permeability.Compaction and calcite cementation are major factors inducing poor reservoir properties.Four kinds of diagenetic facies are classified in Zhenbei Area on the basis of diagenetic characteristics and influence of diageness on reservoirs,compaction resisting-dissolution pore diagenetic facies zone is the most favourable area for development of high quality reservoirs;the chlorite cementation-residual pore diagenetic facies zone is the second favorable diagenetic facies zone;compaction dense diagenetic facies and calcite cementation dense diagenetic facies are disadvantageous to the development of reservoirs.