Surfactant stabilized foams have been used in the past for vertical conformance and mobility control in gas enhanced oil recovery processes. Lack of stability of these foams often limits their application. The goal of this study is to investigate the synergistic effects of using a blend of silica nanoparticles (NP) and anionic surfactants on foam stability in both bulk and porous media. First, stability of static foams were studied using surfactants and surfactant-NP mixtures with and without the presence of a crude oil. Second, the foam drainage behavior and thickness of the foam lamella were studied by fluorescence microscopy. Third, mobility of foams were measured by co-injecting the surfactant or surfactant-NP solutions with nitrogen gas through a Berea sandstone core at a fixed foam quality (gas volume fraction). Finally, oil displacement experiments were conducted in Berea cores using these foams. Static foam tests indicate stabilization effect of nanoparticles on surfactant-nanoparticle stabilized foam in the absence of crude oil. Adding nanoparticles in low concentrations (0.3 wt%) improves the foam stability and increases the mobility reduction factor by a factor of two in the absence of oil. Fluorescence and confocal laser scanning microscopy elucidate the trapping of nanoparticles in plateau borders as well as lamellas which retards liquid drainage and bubble coalescence. The core floods with a reservoir crude oil show about 10% incremental oil recovery by an immiscible foam (with the surfactant-NP blend) over water flood. This study shows that nanoparticles have the potential to increase the stability of surfactant-stabilized foams in subsurface applications.

No abstract

The goal of this work is to evaluate stabilization of foams by a combination of nanoparticles and surfactants. Hydrophilic silica nanoparticles (NP) and anionic surfactants were used in this study. Static foams were generated using surfactants and surfactant-NP mixtures with and without the presence of a crude oil. The decay of the foam height with time was studied and half-lives were determined. The foam drainage behavior and thickness of the foam lamella were studied by fluorescence microscopy. Aqueous foams were created in-situ by co-injecting the surfactant or surfactant-NP mixtures with nitrogen gas through a Berea sandstone core at a fixed quality. Pressure drop across the core was measured to estimate the achieved mobility reduction factor (MRF). Oil displacement experiments were conducted in Berea cores using surfactant and surfactant-nanoparticle mixture as foaming agents. Static foam tests indicate stabilization effect of nanoparticles on surfactant-nanoparticle foam stability in the absence of crude oil. Lighter crude oils were more destabilizing to foams than heavier oils. Adding nanoparticles even in low concentrations (0.3 wt %) can significantly improve the foam stability and mobility reduction factor in the absence of oil. As the concentration of nanoparticles increased, mobility reduction factor (MRF) of surfactant-nanoparticle foam in a Berea core increased significantly. Fluorescence microscopy elucidated that nanoparticles are trapped in the plateau border as well as lamellas which retard liquid drainage and bubble coalescence. The core floods with a crude oil revealed that the incremental oil recovery by surfactant-NP blend over water flood was about 10% OOIP with an immiscible foam.

Foams for subsurface applications are traditionally stabilized by surfactants. The goal of this work is to study foam stabilization by nanoparticles-in particular, by in-situ surface-hydrophobization of hydrophilic nanoparticles. The interfacial properties of the nanoparticles were modulated by the attachment of short-chain surface modifiers (alkyl gallates) that render them partially hydrophobic, but still fully dispersible in water. First, static foams were generated with nanoparticles with varying concentrations of surface modifiers. The decay of foam height with time was measured, and half-lives were determined. Optical micrographs of foam stabilized by surface-modified nanoparticles (SMNPs) and surfactant were recorded. Second, aqueous foams were created insitu by coinjecting the SMNP solutions with nitrogen gas through a Berea sandstone core at a fixed quality. Pressure drop across the core was measured to estimate the achieved resistance factor. These pressure-drop results were then compared with those of a typical surfactant (alpha olefin sulfonate, alkyl polyglucoside) under similar conditions. Finally, oil-displacement experiments were conducted in Berea cores with surfactant and SMNP solutions as foaming agents (coinjection with nitrogen gas). A Bartsch shake test revealed the strong foaming tendency of SMNPs even with a very low initial surface-modifier concentration (0.05 wt%), whereas hydrophilic nanoparticles alone could not stabilize foam. The bubble texture of foam stabilized by SMNPs was finer than that with surfactants, indicating a stronger foam. As the degree of surface coating increased, the resistance factor of SMNP foam in a Berea core increased significantly. The corefloods in the sandstone cores with a reservoir crude oil showed that immiscible foams with SMNP solution can recover a significant amount of oil (20.6% of original oil in place) over waterfloods.

The goal of this work is to develop a novel way of beneficially utilizing two main waste products from coal power-generation plants -carbon dioxide and fly ash -by generating fly ash nanoparticle-stabilized CO 2 foam for CO 2 EOR mobility control. First, as the grain size of fly ash is generally too large for injection into reservoirs, it was reduced to nano-size by the ball-milling process. Second, dispersion stability analysis was performed to evaluate a suitable dispersing agent for fly ash nanoparticles (FA-NP). A range of surfactants (anionic, cationic, and non-ionic) was used in dilute concentrations. Surfactants were screened based on particle-hydrodynamic diameters and polydispersity index of the dispersion as measured by dynamic light scattering. Third, foam flow experiments were performed using combinations of FA-NP and various surfactants. Aqueous foam was created in-situ by coinjecting the FA-NP and/or surfactants with liquid CO 2 through a sandpack at a fixed foam quality. Foam texture, as seen in the view-cell, was used to screen suitable surfactants that stabilized strong foams. Finally, the foam flow experiments were conducted in a Berea sandstone core. Pressure drop across the core was measured to estimate the achieved foam resistance factor and the apparent viscosity of the generated foam. Nanomilling and thermal treatment processes were able to yield thermally-treated fly ash (TTFA) nanoparticles with an average size of 180 nm. Dispersion stability analysis revealed that anionic and non-ionic surfactants are suitable in dispersing these nanoparticles. Foam texture visualization demonstrated that strong carbon dioxide-in-water foam/emulsion with fine texture can be generated using TTFA nanoparticles in porous media in conjunction with a non-ionic surfactant or an anionic surfactant in dilute concentrations. Foam flow experiments in a Berea core showed that TTFA nanoparticles even in low concentrations (0.4 wt%) can significantly improve the foam stability and foam resistance factor of an anionic surfactant (in the absence of oil). Antagonistic effects were observed in foam stability in Berea core by addition of TTFA nanoparticles to nonionic surfactants. This study has the potential of not only to minimize the surfactant usage for foam-based CO 2 EOR mobility control, but also to sequester both CO 2 and fly ash in subsurface formations.