Enhancing the physical plugging behavior of colloidal silica nanoparticles using binomial size distribution

• Enhanced plugging behavior of nanoparticles by optimization of size distribution.
• Enhanced colloidal stability of PEG-coated silica nanoparticles.
• Minimization of pore pressure transmission into clay-rich formation.
• Decreased cost of drilling process by reduction of the amount additives required.

Silica nanoparticles were amply used as one of the common drilling fluid nano-sized additives. Polyethylene glycol-coated colloidal silica nanoparticles with binomial size distribution were prepared and dispersed in water-based drilling fluid. Dynamic light scattering (DLS) analysis shows that the size distribution of nanoparticles has two peaks at 20.5 nm and 115 nm. Intact plugs from a well-preserved clay-rich carbonate formation were obtained and were characterized using X-ray Powder Diffraction (XRD) analysis and Field Emission Scanning Electron Microscope (FE-SEM) observations. Pore Pressure Transmission (PPT) technique was used to investigate the effect of nanoparticles on pressure penetration through the rock sample. Effect of size distribution of nanoparticles on the plugging process was studied and the performance of silica nanoparticles in water-based drilling fluid was optimized. The colloidal silica nanoparticles with binomial size distribution proved superior plugging performance to monodisperse nanoparticles. In addition, due to improved plugging, satisfactory results were obtained using lower concentration of nanoparticles in the drilling fluid. Drilling fluid with 7 wt% silica nanoparticles with binomial size distribution showed the same satisfactory results as the drilling fluid with 10 wt% monodisperse silica nanoparticles. Moreover, polyethylene glycol, as a steric stabilizer, showed excellent performance in reducing the agglomeration among the nanoparticles in aqueous suspensions.