Mechanistic Insights into Dual-Organoclay Interactions for Enhanced HPHT Oil-Based Drilling Fluids

High-pressure and high-temperature (HPHT) drilling operations demand oil-based drilling fluids (OBDFs) with robust rheological stability, strong suspension capacity, and reliable filtration performance. This study investigates the mechanistic and performance advantages of a dual-organoclay (OC) formulation composed of Claytone-SF and Claytone-IMG 400, benchmarked against the individual components and the commercial additive MC-TONE. Comprehensive mineralogical and morphological characterization (XRD, XRF, PSD, SEM) was combined with density, electrical stability, sagging, viscoelastic, rheological, and HPHT filtration testing. The 1:1 dual-OC system increased electrical stability by 17.5%, increased yield point (YP) by 25%, improved the YP/PV ratio by 18.5%, and reduced filtrate volume and filter cake thickness by 17.5% and 12%, respectively. In practical drilling operations, the enhanced YP promotes efficient cuttings transport and Barite suspension, the moderated plastic viscosity (PV) improves hydraulic efficiency by limiting excessive pressure losses, and the reduced filtration loss enhances wellbore stability and reduces formation damage under HPHT conditions. These improvements are hypothesized to arise from a multiscale colloidal network formed by complementary interactions between the plate-like montmorillonite-rich Claytone-SF and the finer, clinochlore-bearing Claytone-IMG 400, leading to tighter particle packing, greater structural resilience, and more stable gel development in the nonaqueous medium. This mineralogical mechanism offers a distinct pathway that complements emerging biobased and surfactant-based shale stabilization strategies. The findings provide new insight into clay–clay interaction behavior in invert emulsions and demonstrate that tailored dual-OC systems can consistently improve OBDF performance under HPHT conditions. These results highlight the potential for mechanistically guided additive design to advance drilling fluid development for complex and thermally stressed wells.