CO2 enhanced oil recovery (EOR) and storage are promising techniques for reducing anthropogenic carbon emissions. Under the appropriate conditions, CO2 pumped into an underground reservoir is contained by multiple trapping mechanisms and sequestered from the atmosphere. One challenge with injecting CO2 into porous media is its low viscosity relative to reservoir brine, leading to viscous fingering and poor sweep efficiency. This problem can be mitigated by injecting CO2 as a viscous CO2-brine foam, which can more efficiently flow through and occupy the reservoir volume, beneficial for both EOR and storage. While most research has focused on surfactant-stabilized CO2 foams, recent advances in nanotechnology have positioned nanoparticle-stabilized foams (i.e. Pickering foams) and synergistic nanoparticle-surfactant foams as potentially more stable alternatives under harsh conditions present in reservoirs, including high temperature, high pressure, and high salinity. The purpose of this work is to graft silica nanoparticles with different surface coatings and measure the resulting nanoparticle-surfactant foam stability under harsh conditions, optimizing for the appropriate surface modification. We attach varying amounts an amine ligand (which grants particle stability) and dimethoxydimethylsilane (DM, which increases hydrophobicity) to bare silica nanoparticles, ranging from 1-12 μmol ligand added per m2 of particle surface. We first screen modified particles for stability to aggregation at up to 80 °C in concentrated brine (&gt;20 wt%), and then co-inject them with CO2 and surfactant at 80 °C and 2200 psi into a 180 μm beadpack. We characterize the stability of the resulting foam by measuring the apparent viscosity via pressure drop across the beadpack and by observing the increase of CO2 bubble diameter in a view cell over several days. Special care is taken to ensure that the entire system is insulated at high temperature and maintained at high pressure. We observe that the most stable nanoparticle-surfactant foams are produced by particles with large amounts of amine ligand and moderate amounts of DM attached to the surface – enough to guarantee particle stability and make the particles somewhat less hydrophilic. These results demonstrate the stability of properly designed nanoparticle-surfactant foams to harsh conditions and help expand the range of reservoir conditions that they could be successfully deployed in for CO2 EOR and storage.

Effect of particle surface modification on the stability of nanoparticle-surfactant-stabilized foams under harsh reservoir conditions

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.