The Effect of Kaolinite on Calcium Carbonate Water-Based Drilling Fluid

This study evaluates the effect of kaolinite addition on calcium carbonate water-based drilling fluids (WBM) through systematic laboratory testing. Kaolinite was incorporated at concentrations of 42.8 kg/m³ (15 lb/bbl), 85.6 kg/m³ (30 lb/ bbl), and 128.4 kg/m³ (45 lb/bbl) into a standard CaCO_3-based WBM, and its influence on density, pH, filtration, rheology, and viscoelastic behavior was analyzed. The density of the base mud (10.15 g/cm³) increased to 11.00 g/c cm³ with 128.4 kg/m³ (45 lb/bbl) kaolinite, while pH rose proportionally with kaolinite content. Filtration tests at 93°C (200°F) and 2.07 MPa (300 psi) revealed that the base sample produced a filter cake thickness of 0.0098 in, which increased progressively with kaolinite addition. Rheological measurements showed Bingham plastic behaviour across all samples, with apparent viscosity increasing from 25 cP in the base mud to 33 cP at 128.4 kg/m³ (45 lb/bbl). Yield point and gel strength also exhibited consistent growth, indicating improved suspension capacity. Viscoelastic testing confirmed enhanced storage modulus (G’) and gelling effect with higher kaolinite concentrations. These results demonstrate that kaolinite significantly enhances the density, filtration control, and rheological stability of CaCO₃ WBMs, supporting its application as a cost-effective and multifunctional additive in drilling operations.