Surfactants Structured by Nanoparticles to Stabilize CO₂ Foam at High Temperature

Foamed fracturing fluids offer an attractive alternative over conventional stimulation fluids, particularly in water-sensitive formations, to shorten the flowback period and energize the created fracture geometry. The thermal stability of foam at high temperatures is one of the main challenges. The gas-liquid interface of foam tends to collapse with temperature. In this paper, CO₂ foam stability is enhanced by nanoparticles structurally supporting foaming agents at high temperature. Nanoparticles (NPs) have a tendency to stabilize foam formulations under harsh conditions of temperature and salinity. In this study, different sizes of SiO₂ NPs (7 nm, 30 nm) were utilized to enhance the stability of CO₂ foam. The NPs were characterized by various techniques such as XRD, TEM, DLS, and BET surface area measurements. The foaming characteristics of various formulations were analyzed by a dynamic foam analyzer (DFA-100), respectively. Rheological properties of CO₂-based foams were measured by circulating flow loop foam rheometer at high temperature (250 °F) and shear rate up to 500 1/s. CO₂ foam stability is enhanced by optimizing the concentrations of CTAB surfactant and silica nanoparticles at high temperature. According to XRD findings, CS-7 and CS-30 are amorphous materials with hexagonal crystal structure. The average diameter of CS-7 and CS-30 silica NPs, as shown by FETEM images, is 12 nm and 25 nm, respectively. CS-7 has a surface area (SBET) that is 2.27 times more than CS-30 sample. CS-7 silica NPs were confirmed to have a more uniform shape, a smaller particle size, and a larger surface area based on these findings. Both CS-7 NPs and the CS-7+CTAB formulation have zeta potential values of -36.9 and 42.1 mV, which support the stability of the foamed colloidal suspension and the development of a densely packed particle arrangement at the liquid/gas interface, respectively. The foam analysis results demonstrate that adding CS-7 silica nanoparticles (0.005 weight percent) to a CO2-based formulation increases foam stability by up to 12%, demonstrating the ability of nanoparticles to stabilize foam formulations. The NPs stabilized CO₂ foamed fluids’ rheological characteristics exhibited 12 cp at 100 1/s utilizing water as the external phase at 2000 pressure and 250°F. Maintaining the stability of CO₂ foam was a challenging task, especially at high temperatures. The stability of CO₂ foam greatly depends upon the optimum hydrophilic-lipophilic balance (HLB) of surfactants. This was achieved by optimizing various formulations using suitable CTAB surfactant and silica NPs to overcome water drainage, CO₂ gas diffusion rate, and rupturing of foam at high temperatures.