Performance evaluation of a blended organoclay system for oil-based drilling fluids under HPHT conditions

Abstract

Abstract

Abstract The performance of oil-based drilling fluids (OBDFs) under high-pressure and high-temperature (HPHT) conditions is strongly influenced by organoclay (OC) additives; however, a systematic understanding of how mineralogical composition and particle size distribution (PSD) influence the structure–property relationships in blended OC systems remains limited. This study addresses this gap by investigating the effect of a blended OC system on the rheological behavior, sag resistance, electrical stability, and filtration performance of OBDFs at 275 °F. A 1:1 mixture of illite-rich (Claytone-3) and montmorillonite-rich (Claytone-SF) OCs was evaluated against individual OCs and a commercial reference (MC-TONE) within a controlled formulation framework. The blended system demonstrated significant performance enhancement, with yield point increasing by approximately 37.5% and gel strength by up to 30% compared to individual formulations. Filtration performance improved, as indicated by a reduction in filtrate volume by about 10.5% and filter cake thickness by approximately 8%. The blended system also exhibited higher electrical stability and reduced static and dynamic sag, indicating improved suspension capacity and emulsion stability under HPHT conditions. These improvements are attributed to complementary mineralogical and morphological characteristics, where a broader particle size distribution promotes enhanced particle packing and formation of a more interconnected gel network. The findings establish a structure–property relationship linking mineralogy, particle size distribution, and macroscopic fluid performance. This study demonstrates that controlled blending of OCs can systematically enhance drilling fluid performance without increasing additive dosage, providing a practical and scalable approach for optimizing OBDF formulations under elevated temperature conditions.