Clay minerals，especially authigene kaolinite，are abundant in the dawsonite-bearing sandstone from the Gudian and Qian'an regions in the southern Songliao Basin． The relationship between dawsonite and kaolinite has been investigated based on drilling data from 50 wells in the Jilin Oil Field and petrological characteristics analyses on 23 core samples from the Gudian and Qian'an regions． The study revealed a negative relationship between the content of dawsonite and kaolinite，suggesting that kaolinite was replaced by the dawsonite． Combined with thermodynamics and geochemical analysis published previously，it is concluded that kaolinite is unstable under CO2-rich environments and can transform into dawsonite．