Nanoparticles-Enhanced Ester-Based Drilling Fluid: A Comprehensive Study on the Influence of Nanoparticles Characteristics on Rheology, Lubricity, HPHT Performance, and Phytotoxicity

Synthetic-based drilling fluids (SBFs) are a sustainable alternative, offering environmental compatibility and superior functional benefits at high pressure and high temperature (HPHT) conditions. However, research on nanoparticles (NPs)-enhanced SBFs remains limited under critical conditions, particularly in systems formulated with biodegradable ester-based oils. This study examines the effects of SiO2, TiO2, and CaCO3 NPs (0.5–1.5 wt %) on enhancing the performance of ester-based drilling fluids (EBFs). Rheological parameters of the formulated drilling fluid samples were measured before and after aging at 150 °C for 16 h, with flow behavior assessed from 30 to 150 °C. Filtration tests were conducted at 150 °C, 400 psi, and the filter cake morphology was analyzed using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Lubricity analysis revealed the coefficient of friction (CoF) remained below 0.15 even after aging, indicating excellent lubrication performance of NPs-EBFs. Phytotoxicity tests assessed the environmental impact, showing significant toxicity differences among the different NPs-EBFs. The optimum rheological properties were observed around 0.5–1 wt % for NPs, while higher concentrations led to reduced efficiency due to agglomeration of particles. SiO2 NPs (0.5–1 wt %) outperformed the other NPs by enhancing rheological stability after thermal aging, reducing HPHT filtrate loss (2 mL), achieving the lowest CoF, highest seed germination rate (120%), and demonstrating superior operational performance and environmental benignity.