Diagenesis of Chang₄₊₅ formation sandstones and its impact on reservoir property in southwest Zhidan region in Ordos basin

The paper is aimed at making clear the distribution of the favorable reservoirs in chang₄₊₅ of Zhidan regions.Based on core description,cast section,scanning election microscope,x-ray diffraction etc,it was believed that the main diagenesis types were pressure solution,cementation and dissolution.Intensive compaction and cementation resulted in complete loss of primary porosity.It was the main reason which formed the low porosity and the lowest permeability;however,the later weak dissolution had great effect on improvement of reservoir permeability,hence,there are some efficient reservoir and become advantaged reservoir-diagenetic facial belt in Yangchang formation in Ordos basin.