Abstract:

To ascertain sandstone diagenesis of the Yanchang Formation and its effects on physical properties, multiple analysis methods were adopted, including general  slice and casting slice identification of sandstone, scan electron microscope， X-ray diffraction, etc. The result shows that feldspar sandstone is the main sandstone type, with low composition maturation and high fabric maturation，and compaction is one of the main causes for porosity losses，and the primary porosity loses further under cementation which is also the main cause of this compact sandstone， especially， cabonate，secondly，quartz increasing margin and kaolinite，but cementation of chlorite film can restrain compaction and is benifical to preserve primary porosity. Physical properties of sandstone reserviors can be improved by dissolution，especially，of feldspar during the later period of diagenesis. Diagenesis reaches A-period of later diagenesis stage，secondary porosity developed by dissolution is one of the main porosity-type of this period，where it is developed well is the favourable reserviors area.

Key words: diagenesis, porosity evolution, Yanchang Formation, Zhidan area, Ordos basin