Pore-scale insights into the effect of surface-modified nanosilica on invert-emulsion drilling-fluid and formation damage

Formation damage caused by drilling mud invasion poses significant challenges. This paper provides novel insights into the pore-scale mechanisms of the damage induced by the invasion of oil-based drilling fluid using a microfluidic technique. The experiments cover well life-cycle consisting of drilling fluid circulation, post-drilling acid treatment, and oil flowback. The focus is on damage remediation by employing nano-drilling fluids containing bare silica (BS) and newly synthesized nanoparticles with enhanced hydrophobicity: GPTS (3-glycidoxypropyl-triethoxy silane), DGPTS (double amount of GPTS), and PGPTS (propyl silane combined with GPTS). Two types of damage were identified through pore-scale imaging. The primary damage mechanisms include pore 'plugging and water blockage, which result from the deposition of solid particles and the breakage of the invert-emulsion. This breakage occurs due to the partial miscibility of the emulsion (or mud) with oil, leading to drilling fluid instability. Secondary damages, which occur in later stages of the well life-cycle, include acid trapping, acid sludge formation, and the creation of acid-in-oil emulsions. These issues arise from the interaction between mud, acid, and oil. We show that both type of damages can be mitigated by stabilizing the invert-emulsion and solid particles using nanoparticles. A balance exists between nanoparticle's surface chemistry and its optimal concentration. Nano fluids with 0.5 wt. % PGPTS, 0.5 wt. % DPGTS, 1 wt. % GPTS, and 1.5 wt. % BS caused the least formation damage, while their performance diminishes at concentrations above these limits. These findings reveal how balancing nanoparticle concentration and hydrophobicity can aid in mitigating the damage.