Search

Nanoparticle (NP)-stabilized foam technology has found potential applications in CO 2 enhanced oil recovery (EOR) and greenhouse gas geological storage practices and accordingly attracts lots of research interest. To screen the optimal formula for the satisfactory foam performance, orthogonal experimental design (OED) is used in this paper for the complex multifactor multilevel system consisting of five influential factors of NP size, surfactant concentration, NP concentration, temperature, and salinity at four different levels in the range of 7-40 nm, 0-0.15 wt %, 0-0.2 wt %, 25-55 °C, and 0-3 wt %, respectively. Based on the orthogonal principle, only 16 experiments were performed to analyze the effect of various factors on the foam height and foam half-life properties. In addition to showing that the influence of the single factor on foam static properties, OED results reveal that the surfactant concentration and temperature are dominating factors on foamability and stability of the NP-stabilized CO 2 foam, respectively. Finally, NP-stabilized CO 2 foam with satisfactory static characteristics is obtained with the OED recommended composition of a 0.15 wt % surfactant concentration, 0.1 wt % NP concentration, and NP size of 7 nm in 1 wt % saline solution at temperatures of 30 and 50 °C, validating that the OED method could substantially facilitate the laboratory screening and optimization process for a successful NP-stabilized CO 2 foam application., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

In order to improve the CO 2 foam stability at high temperature and salinity, hydrophilic silica nanoparticles (NPs) were added into a dilute zwitterionic surfactant solution to stabilize supercritical CO 2 (SC-CO 2 ) foam. In the present paper, the foaming capacity and stability of SC-CO 2 foam were investigated as a function of NP concentration at elevated temperatures and pressures. It was observed that the drainage rate of SC-CO 2 foam was initially fast and then became slower with NPs adsorption at the gas-liquid interface. The improved foam stability at high temperature was attributed to the enhanced disjoining pressure with addition of NPs. Furthermore, an obvious increase in the foam stability was noticed with the increasing salinity due to the screening of NP charges at the interface. The rheological characteristics including apparent viscosity and surface elasticity, resistance factor, and microstructures of SC-CO 2 foam were also analyzed at high temperature and pressure. With addition of 0.7% NPs, SC-CO 2 foam was stabilized with apparent viscosity increased up to 80 mPa·s and resistance factor up to 200. Based on the stochastic bubble population (SBP) model, the resistance factor of SC-CO 2 foam was simulated by considering the foam generation rate and maximum bubble density. The microstructural characteristics of SC-CO 2 foam were detected by optical microscopy. It was found that the effluent bubble size ranged between 20 and 30 μm and the coalescence rate of SC-CO 2 foam became slow with the increasing NP concentration. Oscillation measurements revealed that the NPs enhanced surface elasticity between CO 2 and foam agents for resisting external disturbances, thus resulting in enhanced film stability and excellent rheological properties., (Copyright © 2019 Li, Wei, Xiong, Ouyang, Shao, Dai, Liu and Du.)