Surfactants Structured by Nanoparticles to Stabilize CO2 Foam at High Temperature

Abstract 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.