Stable CO2/water foam stabilized by dilute surface‐modified nanoparticles and cationic surfactant at high temperature and salinity

Abstract CO 2 enhanced oil recovery and storage could see widespread deployment as decarbonization efforts accelerate to meet climate goals. CO 2 is more efficiently distributed underground as a viscous foam than as pure CO 2 ; however, most reported CO 2 foams are unstable at harsh reservoir conditions (22 wt% brine, 2200 psi, and 80°C). We hypothesize that silica nanoparticles (NP) grafted with (3‐trimethoxysilylpropyl)diethylenetriamine ligands (N3), to improve colloidal stability, and dimethoxydimethylsilane ligands (DM), to improve CO 2 ‐phillicity, combined with the cationic surfactant N 1 ‐alkyl‐ N 3 , N 3 ‐dimethylpropane‐1,3‐diamine (RCADA), will develop viscous, stable CO 2 foams at reservoir conditions. We grafted NP with N3 and DM ligands. We verified NP stability at reservoir conditions with measurements of zeta potential, amine titration curves, and NP diameter. We measured NP water contact angles ( θ w ) at the water–air and water–liquid CO 2 interfaces. In a high‐temperature, high‐pressure flow apparatus, we calculated the viscosity of CO 2 foams across a beadpack and determined static foam stability with microscope observations. Modified NP were colloidally stable at reservoir conditions for 4 weeks, and had higher θ w in liquid CO 2 than in air. Addition of at least 0.5 μmol/m 2 DM silane (0.5DM) greatly improved foam stability. RCADA‐only foam coarsening rates ( dD SM 3 / dt ) decreased 16–17× after adding 1 wt/vol% 8N3 + 1.5DM NP, and 5–10× with a 0.1–1 vol/vol% increase in RCADA concentration (with or without NP). 1 vol/vol% RCADA foam exhibited coarsening rates of 900 and 2400 μm 3 /min with 1 and 0.2 wt/vol% 8N3 + 1.5DM NP, respectively. These results demonstrate impressive foam stabilities at harsh reservoir conditions.