Diagenesis of Chang 6 reservoir of Yanchang formation in Fuhuang exploration area of the Ordos basin

On the basis of analysis of thin section observation,casting lamella,scan electron microscope and X-ray diffractions etc,the study area was determined to be a the low porosity and low permeability reservoir, whose sandstone types are arkose sandstone and lithic arkose sandstone.They are mainly in re-angular and re-round round forms,line and point-line contact forms with pore and pore-thin film cementation between rock grains.The study reservoir is mainly characterized by low compositional maturity and high textual maturity. The diagenetic factors of Chang 6 reservoir include compaction,cementation,corrosion and disruption.The compaction in the early diagenetic phase,which resulted in 30.89%porosity loss,is the main factor causing the loss of porosity for the sandstone.Cementation resulted in 6.98%average porosity loss,and carbonate and quartz overgrowth are the main cements that have reduced the reservoir quality.But the solution has added an extra 1.22%porosity to the reservoir,which is an important way to improve the reservoir quality for the sandstone.