Carbon dioxide (CO 2 ) has found wide application in the water-alternating-foam (WAF) processes for enhanced oil recovery (EOR), but few research works have been reported concerning the effect of water solubility on the CO 2 foam rheology in a porous medium. In this paper, an X-ray computed tomography (CT) study is carried out to investigate CO 2 foam flow in a consolidated Bentheimer sandstone core saturated with surfactant solution under different system pressures. As a contrast gas with much lower solubility, nitrogen foam flow is also investigated to show the essence of gas solubility effects. Careful considerations were made on the selection of contrast gases, surfactant, and experimental procedures to focus on the effect of water solubility of the gas on foam rheology in porous media. It is observed from the experiments that CO 2 foam has lower pressure loss and clearly suppressed entrance effect. With the increment of system pressure, the liquid saturation increases and the pressure loss decreases significantly for CO 2 foam flow in the sample core, while little change can be observed for N 2 foam flow. It can be concluded that water solubility is one of the important influential factors for CO 2 foam rheology in porous media.

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Developing high-efficiency dual-functional catalysts to promote oxygen electrode reactions is critical for achieving high-performance aprotic lithium–oxygen (Li–O2) batteries. Herein, Sr and Fe cation-codoped LaCoO3 perovskite (La0.8Sr0.2Co0.8Fe0.2O3−σ, LSCFO) porous nanoparticles are fabricated as promising electrocatalysts for Li–O2 cells. The results demonstrate that the LSCFO-based Li–O2 batteries exhibit an extremely low overpotential of 0.32 V, ultrahigh specific capacity of 26 833 mA h g–1, and superior long-term cycling stability (200 cycles at 300 mA g–1). These prominent performances can be partially attributed to the existence of abundant coordination unsaturated sites caused by oxygen vacancies in LSCFO. Most importantly, density functional theory (DFT) calculations reveal that codoping of Sr and Fe cations in LaCoO3 results in the increased covalency of Co 3d–O 2p bonds and the transition of Co3+ from an ordinary low-spin state to an intermediate-spin state, eventually resulting in the transformation from nonconductor LCO to metallic LSCFO. In addition, based on the theoretical calculations, it is found that the inherent adsorption capability of LSCFO toward the LiO2 intermediate is reduced due to the increased covalency of Co 3d–O 2p bonds, leading to the formation of large granule-like Li2O2, which can be effectively decomposed on the LSCFO surface during the charging process. Notably, this work demonstrates a unique insight into the design of advanced perovskite oxide catalysts via adjusting the covalency of transition-metal–oxygen bonds for high-performance metal–air batteries.

Summary Carbon dioxide (CO2) foam has been widely studied in connection with its application in enhanced oil recovery (EOR). This paper reports an experimental study concerning CO2 foam propagation in asurfactant-saturated Bentheim sandstone core and the subsequent liquid injection with the aid of X-ray computed tomography (CT). The experiments were carried out under various system backpressures. It is found that CO2 foam flows in a characteristic front-like manner in the transient stage and that the water saturation keeps at relatively high level at the outlet of the porous media because of CO2 solubility and capillary end effect. The subsequent surfactant solution injection shows a significant fingering behavior, accompanied by a low flow resistance over the core. It is also found that CO2 foam flow shows higher liquid saturation near the outlet and lower pressure drops under higher system backpressures. This can be attributed to the solubility of CO2 in the liquid phase. The results indicate the advantage of using foam in EOR processes such as water alternating foam (WAF), in which foam flow has higher sweep efficiency and stronger mobility control ability compared, for instance, to water alternating gas (WAG). Nevertheless, care should be taken during the water-injection stage in order not to favor the fingering. Introduction Foam applications in EOR and fluid (acid) diversion have grown considerably over the last three decades. For instance, WAGhas been regularly used in the field as a gasflood mobility control measure. Nevertheless, this technique has not always demonstrated the desired beneficial mobility effects because of the gravity segregation and the unstable preceding of the front between the water and moremobile gas (Holm 1987; Smith 1988). Creating foam by adding surfactant to the aqueous phase has proven to be able to increase the total recovery significantly by increasing the apparent viscosity of the system (Holm and Josendal 1974; Ali et al. 1985; Patzek 1996; Zhdanov et al. 1996; Turta and Signhal 1998). There are many attractive features of EOR using CO2 foaminjection. First, carbon dioxide is a proven solvent for reconnecting, mobilizing, and recovering waterflood residual oil. Many studies (Stalkup 1983) have shown that CO2 can achieve miscible-like displacement efficiency through multiple contacts (partitioning and extraction) with the crude oil. Second, CO2 is available naturally in large quantities and as a byproduct of lignite gasification and many manufacturing processes. Its price is also low, and there are no other large-volume uses competing for CO2. Third, with the push toward sustainable power production and the increasing realization for the need to reduce CO2 emissions, EOR using CO2 is becoming an important alternative for geological CO2 storage.