Clay fractions and fluid inclusions were studied in the Aulnay sous Bois and Cerneux (CER-1 and CER-P6) wells located 10 km, 1.3 and 0.6 km, respectively, from the ＇＇Pays de Bray＇＇ fault (Paris Basin, France). It was shown that a connection was probably established between the Dogger and Triassic reservoirs during the active period of the fault. Chemical and heat transfers have locally modified the diagenesis conditions in the Dogger formation, inducing an overmaturation of clay minerals. These effects, although attenuated, are still identifiable in the Aulnay and CER-1 wells. A maximum temperature of about 90-degrees-C was maintained in CER-P6 site even during the uplift stage of the basin.