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Drilling fluids are formulated with a range of additives to achieve the desired functional properties including specific rheological properties. Its rheology, a critical property, is sensitive to the chemicals used in its formulation and the environment encountered during drilling. The flow and time-dependent behaviour of bentonite slurries were evaluated under the influence of KCl and P₂O₇⁴⁻ or MgCl₂ and P₃O₁₀⁵⁻ at specific concentrations. The multi-charge phosphate anions weakened the gel and its ageing behaviour at low KCl or MgCl₂ content. At high KCl concentration, the sequence of salt addition in the gel preparation has a significant effect on the gel strength and stability. The gel was very strong when the platelets were allowed to exfoliate before the salt addition. When the delamination was hindered, a weak and at time an unstable gel was produced as a result of low platelet concentration. The gels prepared …