Quantitative study on diagenesis in reservoirs with extra-low to ultra-low permeability in the Member 4 of Lower Cretaceous Quantou Formation in Da'an Oilfield,Songliao Basin

The diagenetic types,intensity,and the influence factors of extra-low to ultra-low permeability reservoirs of the Member 4 of Cretaceous Quantou Formation in Da'an Oilfield are analyzed by using data of thin section,casting thin section,SEM,physical properties,logging explanation and particle size analysis. The results show that:( 1) Compaction is the dominant diagenesis which leads to the loss of the pore. The compaction degree is medium,which has a good correlation with the compound sand thickness,sorting coefficient,mud content etc.( 2) The carbonate cementation is the second important factor for the poorer physical properties of reservoirs. The cementation degree is quite weak,and the decrease of the porosity caused by cementation is related to the distance from the reservoir to the configuration surface,quartz content,clastic component content and matrix content.( 3) The dissolution degree is relatively weak,which can improve the physical properties of the reservoirs. The increased porosity ratio by diss