The Kong一1 and一2 members are major oil--bearing sequences in the Zaobei Oil Field．The contents of clay minerals and their manners of occurrence in sandstone have been analyzed by means of thin--section analysis，scanning electron microscopy’and X—ray diffraction analysis and their vertical distribution and evolution have been studied．The ef— fects of clay minerals on reservoir physical properties have also analyzed．The sensitivity of various reservoirs has been evaluated on the basis of the reservoir sensitivity tests．