In the onshore Congolese coastal basin, a borehole (kundji-203) encountered a sandstone reservoir from 1480 m MD. Three Runs of 27m each were lowered into the well at the level of the Top-reservoir for the purpose of an in-depth study. The lithological study of this reservoir shows that it is made up of a succession of four compact sandstone levels, interspersed with clayey layers. Its present facies is made up of very fine to medium grains, sometimes coarse or sometimes conglomeratic, brown with clay-carbonate cement. The clayey pastes are gray to greenish, indurated, flaky. The figured elements are made up of rock debris. The mineralogical study of the clay process shows the presence of four types of clay, the most abundant of which is chlorite, followed by illite or smectite and some rare traces of kaolinite.