Silica Nanoparticles for the Stabilization of W/O Emulsions at HTHP Conditions for Unconventional Reserves Drilling Operations

A novel generation of drilling fluids based on the principle of Pickering emulsions was prepared in this work using three different types of commercial silica nanoparticles with various hydrophobicity and particle sizes. We demonstrated that a threshold of nanoparticles concentration was necessary to stabilize the emulsions which strongly depended upon the particles wettability (hydrophobicity) and sizes. Nonetheless, on increasing the water phase volume fraction, a catastrophic inversion from Water-in-Oil (W/O) to Oil-in-Water (O/W) was obtained for emulsions prepared using amphiphilic silica nanoparticles. Particles wettability has proven to be strongly affected by the pH of the aqueous phase. However, changing the salinity of the brine phase did not have remarkable effects neither on the stability to coalescence/sedimentation nor on the droplet size distribution of the emulsions prepared. Oscillatory rheology illustrates that addition of clay particles boosts fluids thixotropic properties which experienced full recovery of gel strength even after aging. The drilling fluids prepared were aged for 16 h at 350 °F (177 °C) and 500 psi (35 bar) and provided high stability contrary to surfactant stabilized Oil-Based-Mud (OBM) that failed completely after aging