The effect of metal ions on the stability and properties of a KCl-polymer based drilling fluid

• Trivalent ions (Fe³⁺, Al³⁺) caused the greatest destabilization, leading to rapid barite sedimentation, reduced electrostatic repulsion, and increased aggregation, while monovalent and divalent ions had minimal short-term effects. • Long-term tests showed that all ion types induced settling, with monovalent and divalent ions contributing more significantly to progressive barite compaction over 45 days, highlighting time-dependent destabilization. • XRD analysis showed no new crystalline phases, confirming that destabilization was driven by colloidal interactions rather than dissolution–precipitation reactions of barite. • Rheological amplitude sweep tests revealed reduced elasticity and higher yield stress in fluids contaminated with trivalent ions, underscoring their adverse impact on both stability and mechanical properties. This paper presents an analysis of destabilization of barite particles on a KCl-polymer based drilling fluid, focusing on the impact of metal ions. The inherent stability of base fluids is characterized by rheology, shear-dependent viscosity, elasticity, and electrostatic repulsion between negatively charged colloids. However, the introduction of metal ions, particularly trivalent ions-significantly alters these dynamics. Short-term stability assessments revealed a measurable reduction in solid levels (up to ∼14%) and increased final separation, attributed to diminished electrostatic repulsion and enhanced particle aggregation. Trivalent ions induced substantial instability, while monovalent and divalent ions have minimal short-term effects. Sedimentation analyses demonstrated that trivalent ions contamination consistently reduced the solid levels, especially at elevated concentrations, with rapid settling during the initial hours followed by slower compaction over time. A trend observed between ion concentration and settling extent. Long-term sedimentation showed increased total settling, with monovalent and divalent ions exhibiting delayed but noticeable instability compared to initial observations. Controlled pH evaluations indicated that while trivalent ion hydrolysis lowered fluid pH, destabilization was primarily driven by charge neutralization rather than acidity. X-ray diffraction analysis confirmed no formation of new crystalline phases, suggesting that sedimentation resulted from physical flocculation rather than dissolution–precipitation reactions. Rheological amplitude sweep tests further underscored the role of trivalent ions in enhancing the solid-like character of the fluid while reducing elasticity and overall stability. These findings highlight that trivalent ion contamination, such as iron leached from casing walls, poses a critical risk to fluid stability during drilling and completion operations, while prolonged exposure to any metal ion type may lead to compacted settled barite over time.