Adaptability of evaluation methods for the inhibitory effect of potassium-based inhibitors in drilling fluids

Shale borehole instability induced by clay hydration and swelling remains a critical challenge in drilling engineering. Although potassium-based inhibitors are widely used, their effectiveness is often inconsistent or unclear due to variations in evaluation methods. This study systematically compared three potassium salts– potassium chloride (KCl), potassium silicate (K 2 SiO 3 ), and potassium polyacrylate (KPAM)-using core immersion tests, linear expansion tests, zeta potential tests and hot rolling recovery tests. The adaptability of each method was assessed in terms of sample type, inhibitor dosage, and experimental duration. Results showed that KPAM performed strongly in core immersion tests, whereas KCl and K 2 SiO 3 caused rapid core disintegration, with KCl causing even faster breakdown than observed in deionized water. Linear expansion tests revealed a significant concentration dependence: expansion strength exceeded that of deionized water at concentrations below 3 % ( w / v ) for KCl, 1 % (w/v) for K 2 SiO 3 , and 0.1 % (w/v) for KPAM. In core drop staining tests, K 2 SiO 3 formed a dense adsorbed film on bentonite cores. The study highlights key methodological limitations: core immersion tests are unsuitable for assessing inorganic salt inhibitors. Zeta potential analysis reflected changes in clay particles surface charge but did not consistently correlate with inhibition effectiveness. Rolling recovery tests offer strong reproducibility and broad applicability but require consistent base fluid properties. Core drop staining tests provide a novel approach for characterizing film-forming inhibitors. These insights can support the future development and evaluation of high-performance shale inhibitors. • K₂SiO₃ and KPAM form films via anions, enhancing the inhibitory effect of K + . • Linear expansion tests require at least 24 h and high concentrations. • Shale rolling recovery is positively correlated with test solution viscosity. • SEM analysis can be combined with other methods for a comprehensive assessment.