The study developed a model that predicts the swelling of shale as a function of proportion of clay minerals, brine concentration in the mud and cation exchange capacity when exposed to brine. The study also showed that the performance of drilling mud to manage wellbore stability is a function of the mud salinity concentration of the aqueous phase and the salinity of the pore fluid. Shale characterization studies showed the dominance of the palygorskite and kaolinite group of clay minerals; low CEC and low permeability. The mineralogical composition of the shales varied across fields, depth and location even for the same wells. Formation water characterization from the selected fields showed that sodium (Na) and chlorine (Cl) are the dominant cation and anion respectively.