Influence of authigenic chlorite on the relationship of porosity to permeability in the sandstone reservoir:A case study from Chang-8 oil-bearing formation of Triassic in Jiyuan-Huaqing area,Ordos Basin

The content of authigenic chlorite mainly presented in the form of pore-lining cement is the highest in the authigenic clay minerals in Chang-8 oil-bearing formation of Triassic in the Jiyuan-Huaqing area of Ordos Basin.The calculation of content of authigenic chlorite and the relationship between porosity and permeability show that the distribution characteristics of the authigenic chlorite have a direct impact on the relationship of porosity to permeability in the sandstone reservoir.Overall,with the increasing of the content of the authigenic chlorite in sandstone,the porosity tends to increase to obtain the same permeability.However,for different ranges of permeability and contents of the authigenic chlorite,the porosity increases in different degrees to get the same permeability.Based on the principle,when considering the limit of porosity for defining the permeable sandstone or calculating reserves,the content of the authigenic chlorite should be considered.For example,for the permeability of 0.1×10-3μm2 of Chang-8 oil-bearing formation in the Jiyuan-Huaqing area,when authigenic chlorite lacks or has a lower content,the limit of porosity could be 7%~8%,while authigenic chlorite has a higher content,for instance,the chlorite content is 8% ~10% or higher,the limit of porosity could be 9%~10%.