The goal of this study is to experimentally
investigate the stability
and rheological behavior of supercritical CO2 foam in the
presence of nanosilica, a surfactant, and a polymer. First, three
types of surfactants with different charges were used to generate
CO2 foam together with nanosilica under supercritical conditions.
The anionic, cationic, and nonionic surfactants each interacted differently
with the negatively charged silica nanoparticles (NPs). Owing to its
yielding the highest apparent viscosity with nanosilica, the anionic
sodium dodecyl sulfate (SDS) surfactant was selected to generate nanosilica-stabilized
foam with a polymer to further enhance its apparent viscosity. Second,
the thermal resistance of nanosilica-SDS-stabilized CO2 foam was assessed in terms of foam apparent viscosity and stability
under reservoir conditions with higher temperatures. Finally, supercritical
CO2 foams were generated with a combination of nanosilica,
SDS, and 2-hydroxyethyl cellulose (HEC) polymer with various concentrations
at different temperatures. Results show that the anionic SDS surfactant
yielded higher apparent viscosity and foam stability with nanosilica.
An optimal SDS concentration was expected, beyond which no significant
improvement on foam apparent viscosity could be found judging from
the trend of the experiment result. The cationic surfactant dodecyl
trimethylammonium bromide (DTAB) and nonionic Ecosurf EH-9 surfactants
performed similarly and did not yield any significant improvement
in foam apparent viscosity. The addition of the polymer not only yielded
higher apparent viscosity but also improved the thermal resistance
of the NP-SDS-HEC-stabilized CO2 foam. For each combination
of additives, higher temperatures have consistently shown its undermining
effect on foam apparent viscosity and stability. However, the combination
of the NP-SDS-HEC CO2 foam system has shown great improvement
in foam performance compared to the case of foam stabilized with nanosilica
alone. The results of this research suggest a compatibility check
among additives within the fluid before further optimization work
to ensure synergy among these additives. An interactive mechanism
among these additives was proposed, which can explain the experimental
results consistently. The results of this research can be used as
guidance toward the performance optimization of nanosilica-stabilized
CO2 foam for fracturing applications.