Designing and optimizing suitable drilling fluids for permafrost exploration to get gas hydrates at low temperature is one of most essential and urgent demands in the current research on exploration and exploitation of gas hydrates. The issue on rheological properties and maintaining borehole stability of drilling fluids is especially important to focus on. This work studies the gas hydrates and wellbore stability conditions and designs a low solid phase mud system with chemical additives. The

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... easured values and effect on rheological and physical properties of the drilling fluids with different type and concentration of additives are studied. Hydration expansion is tested in laboratory to estimate the hydration property of different additives. It is showed that the drilling fluids with a dose of 1 % HT have suitable rheological and physical properties at low temperature. Potassium ion performs well in preventing borehole instability and gas hydrate dissociation. According to the study, the optimized drilling fluid formula is: base mud + 10 % NaCl + 5 % KCl + 1 ‰ NaOH + 1 % HT.