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Carbon dioxide (CO2) flooding is one of the most globally used EOR processes to enhance oil recovery. However, the low gas viscosity and density result in gas channeling and gravity override which lead to poor sweep efficiency. Foam application for mobility control is a promising technology to increase the gas viscosity, lower the mobility and improve the sweep efficiency in the reservoir. Foam is generated in the reservoir by co-injection of surfactant solutions and gas. Although there are many surfactants that can be used for such purpose, their performance with supercritical CO2 (ScCO2) is weak causing poor or loss of mobility control. This experimental study evaluates a newly developed surfactant (CNF) that was introduced for ScCO2 mobility control in comparison with a common foaming agent, anionic alpha olefin sulfonate (AOS) surfactant. Experimental work was divided into three stages: foam static tests, interfacial tension measurements, and foam dynamic tests. Both surfactants were investigated at different conditions. In general, results show that both surfactants are good foaming agents to reduce the mobility of ScCO2 with better performance of CNF surfactant. Shaking tests in the presence of crude oil show that the foam life for CNF extends to more than 24 h but less than that for AOS. Moreover, CNF features lower critical micelle concentration (CMC), higher adsorption, and smaller area/molecule at the liquid–air interface. Furthermore, entering, spreading, and bridging coefficients indicate that CNF surfactant produces very stable foam with light crude oil in both deionized and saline water, whereas AOS was stable only in deionized water. At all conditions for mobility reduction evaluation, CNF exhibits stronger flow resistance, higher foam viscosity, and higher mobility reduction factor than that of AOS surfactant. In addition, CNF and ScCO2 simultaneous injection produced 8.83% higher oil recovery than that of the baseline experiment and 7.87% higher than that of AOS. Pressure drop profiles for foam flooding using CNF was slightly higher than that of AOS indicating that CNF is better in terms of foam–oil tolerance which resulted in higher oil recovery. [ABSTRACT FROM AUTHOR]

In order to improve the CO2 foam stability at high temperature and salinity, hydrophilic silica nanoparticles (NPs) were added into a dilute zwitterionic surfactant solution to stabilize supercritical CO2 (SC-CO2) foam. In the present paper, the foaming capacity and stability of SC-CO2 foam were investigated as a function of NP concentration at elevated temperatures and pressures. It was observed that the drainage rate of SC-CO2 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-CO2 foam were also analyzed at high temperature and pressure. With addition of 0.7% NPs, SC-CO2 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-CO2 foam was simulated by considering the foam generation rate and maximum bubble density. The microstructural characteristics of SC-CO2 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-CO2 foam became slow with the increasing NP concentration. Oscillation measurements revealed that the NPs enhanced surface elasticity between CO2 and foam agents for resisting external disturbances, thus resulting in enhanced film stability and excellent rheological properties.

[Display omitted] • Physical crosslinking density of composites improved from 0.0083 to 0.0124 mol/cm3. • Strain-hardening behavior of composites improved their foamability. • The shrinkage problem of TPU foam was optimized from 39.8 % to 6.7 % at 130 °C. • BE-Mg 2 B 2 O 5 around the cell wall slowed down the diffusion rate of CO 2. Thermoplastic polyurethane (TPU) foam is eco-friendly prepared with supercritical carbon dioxide (CO 2) as a blowing agent. Magnesium borate whisker (Mg 2 B 2 O 5) modified by borate ester coupling agent (BE) (BE-Mg 2 B 2 O 5) was introduced into TPU to modulate cell nucleation, bubble growth and foam stabilization depending on the intercalation structure of Mg 2 B 2 O 5 , entanglement effect of BE and increased physical crosslinking density. The modulation of Mg 2 B 2 O 5 on the hard segment crystallization promoted hard segment's (HS) microstructure, i.e., physical crosslinking density. The addition of BE-Mg 2 B 2 O 5 enhanced the rheological properties, maximum tensile strength and elongation at break of TPU composites. Excellent mechanical property and strain-hardening behavior of TPU composites improved the foamability of TPU composites. Mg 2 B 2 O 5 and entanglement points acted as heterogeneous nucleation sites to momentously increase cell density and reduce bubble size. Intercalation structure of Mg 2 B 2 O 5 , entanglement effect of BE and high physical crosslinking density effectively limited the TPU relaxation and memory recovery. BE-Mg 2 B 2 O 5 around the cell wall acted as a barrier to slow down the diffusion rate of CO 2 from inside the bubble to outside. The dual action synergistically reduced the shrinkage of TPU foam. [ABSTRACT FROM AUTHOR]

• Introduction of alcohol co-blowing agents significantly changed the crystal structure of PP. • Plasticization effect of alcohol decelerated the diffusion rate of CO 2. • Foaming temperature window was broadened owing to the plasticization effect of alcohol. • Uniform cell morphology with high cell density and small cell size was obtained at low temperature. [Display omitted] A novel approach was established to promote favorable PP foams at low temperatures by regulating the melt crystallization behavior. The crystallization behavior of PP on supercritical CO 2 foaming was systematically studied in the presence of alcohol as co-blowing agent. The results of dissipative particle dynamics (DPD) simulations revealed that the diffusion coefficient of blowing agents in PP was enhanced with the increase of alcohol molecular weight. Alcohols had a significant effect on the melt and crystallization behavior of PP. The crystallization temperature was decreased from 88 ℃ to 82 ℃, and crystallinity declined from 17% to 9% by adding 1-decanol in 8 MPa CO 2. The addition of co-blowing agents decelerated desorption rate of blowing agents. The lower limit of foaming temperature moved further down with the carbon chain growth of alcohol, e.g., the lower temperature decreased from 145 ℃ to 130 ℃ by adding 1-decanol. [ABSTRACT FROM AUTHOR]

Supercritical CO 2 (ScCO 2) foam could benefit both industry revenue generation through EOR and climate control with CO 2 storage/utilization. Relative to aqueous soluble surfactants, it has been experimentally observed that CO 2 -philic surfactants accelerated foam propagation and enhanced oil recovery significantly. It is desired to probe additional potential superiorities with presence of gravity under reservoir conditions. In this paper, comprehensive numerical investigations are conducted to compare the ScCO 2 foam performances with both types of surfactants under variable injection strategies in a homogeneous reservoir. Both constant rate and pressure constraints are examined, where impacts of slug size, volumetric injection phase ratio, perforation location, and phase injection portion are probed. For all tested injection strategies, the novel foam outperforms conventional one with higher oil recovery, injectivity, and injection fluids (surfactant/CO 2) utilization efficiencies. The dual partition capacity of CO 2 -philic surfactant could not only improve the injectivity but also divert CO 2 effectively. The novel injection strategy with dissolved CO 2 -soluble surfactant outperforms others. Also, the novel foam is not sensitive to injection parameter values. Constant pressure injection could provide alike performances as those under constant rate constraint if injection fluids conservations are employed, which revises prior conclusions. The inherent dual phase partition capacity of CO 2 soluble surfactant predominates in fighting gravity segregation and enhancing foam performances, which replaces prior external criteria with aqueous soluble surfactants through injection strategy, constraint and gravity segregation length. The findings here assign significant flexibility during field operation. The comparisons improve understandings of this novel technology and provide guidance for field implementation. [ABSTRACT FROM AUTHOR]