ABSTRACT Wellbore stability problems, especially in reactive shale formations, have gained much attention due to their high cost and technical complications. In this work, the blind use of only chemical osmosis to balance reactive shales, while drilling has been challenged through the use of linear swelling technique and water and ions gravimetric test. Moreover, the compatibility of various aqueous solutions with field shale samples was analysed and a proper mud salinity design method was proposed. Using Na+, K+ and Ca+2 and 100 shale samples and cuttings from a drilling site, a mud salinity (ion’s type and concentration) selection method was proposed. A field case was presented and it was shown that KCl solutions were appropriate to drill shale formations up to 9,717 ft. while NaCl solution was suitable to drill a deeper formation that spans from 9,817 to 10,381 ft. Moreover, CaCl2 solutions were not selected to handle these shales due to their high reactivity and excessive water and ions exchange. Besides chemical osmosis, results showed that water transport may occur due to diffusion osmosis and ionic diffusion. Also, the transport of ions by ionic diffusion was found to be a major destabilizing factor.