Design and performance evaluation of nano-based drilling fluid system for hydrate bearing sediments

Well drilling operations are essential for the exploration and development of natural gas hydrates. However, under specific conditions, drilling fluids can invade reservoirs, leading to borehole instability and distortions in well-logging data. The incorporation of nanoparticles has proven to be an effective method to enhance the anti-filtration and pore or fracture plugging capabilities of drilling fluids, thus improving wellbore stability. Additionally, research has shown that a targeted concentration of hydrophilic nanoparticles can inhibit hydrate formation. This study focuses on hydrophilic nano-CaCO₃ particles as specialized additives for drilling fluids and proposes a nano-based hydrate drilling fluid system. The performance and hydrate inhibition of this modified drilling fluid were comprehensively evaluated. The designed formulation for the simulated drilling fluid was determined to be: 1.0% CMC + 0.1% PAM + 0.1% XC + 5.0% NaCl + 5.0% KCl + 1.0% PVCap + 1.0%–6.0% nano-CaCO₃. The designed drilling fluid system achieved a colloidal stability exceeding 97%, with a density range of 1.08–1.10 g/cm³. Its apparent viscosity ranged from 36 to 79.5 mPa·s, plastic viscosity from 27 to 42 mPa·s, and dynamic shear force from 8.176 to 38.325 Pa. The rheological effects of nanoparticles are concentration-dependent, with minimal changes at 1–4 wt% and significant increases at 5–6 wt%, enabling performance tuning for drilling needs. The pH value of the fluid was approximately 7, which could be modified by the addition of alkaline substances. Furthermore, as the nanoparticle concentration increased, the fluid's filtration rate progressively decreased. Therefore, this nano-CaCO₃-based drilling fluid system demonstrates excellent reservoir protection properties and is well-suited for drilling in marine hydrate-bearing sediments.