Bo Peng

Carbon dioxide micronanobubbles (CO₂ MNBs) hold potential for enhancing gas utilization efficiency and mass transfer performance in fluids related to carbon capture, utilization, and storage (CCUS). However, their stability is significantly constrained in high-salinity environments due to pronounced coalescence and aging. To address this issue, this study proposes an interfacial synergistic regulation strategy based on a composite system of carbon dots (CDs) and zwitterionic/nonionic surfactants to stabilize CO₂ micronanobubbles. Research indicates that carbon dots themselves lack surface activity but can form composite structures with surfactants through hydrogen bonding and electrostatic interactions. This leads to synergistic adsorption at the gas–liquid interface, significantly reducing the minimum surface tension from 21.54 to 10.71 mN·m^–1. The established semiquantitative adsorption model characterizes the nonlinear response of interfacial tension, revealing a competitive relationship between synergistic adsorption and bulk phase dissipation. The formation of the composite interfacial layer effectively suppresses gas diffusion and Ostwald ripening, significantly enhancing the size stability of micronanobubbles. Furthermore, in high-salinity systems enriched with Ca²⁺, carbon dots exhibit pronounced interfacial charge buffering, effectively preventing charge reversal and maintaining bubbles at a stable diameter below 600 nm for 24 h. This study elucidates the mechanism by which carbon dots stabilize CO₂ micronanobubbles through interfacial regulation, providing scientific rationale for designing low-cost, salt-tolerant CO₂ enhanced oil recovery microbubble fluid systems.

Understanding the wettability transition of shale organic matter in CO₂/N₂ environments is crucial for optimizing geological CO₂ sequestration and gas recovery operations. In this study, molecular dynamics simulations were employed to investigate the wettability behavior of kerogen under CO₂ and N₂ atmospheres across a wide range of temperatures (298.15 to 378.15 K) and pressures (5 to 65 MPa). The effects of brine salt type, concentration, and gas mixture composition were also considered. Results show that increasing the CO₂ pressure significantly increases the water contact angle on kerogen surfaces, indicating reduced water wettability. In contrast, N₂ exhibits only a minor effect. Temperature has a weakening effect on contact angles under the CO₂ environment but a negligible influence in the presence of N₂. Salt cations such as Mg²⁺ and Ca²⁺ increase the contact angle more significantly than Na⁺ at the same concentration. Furthermore, as the N₂ proportion increases in CO₂-N₂ mixtures, water contact angles decrease, revealing a stronger adsorption affinity of CO₂ on shale organic matter. These findings provide molecular-level insights into how geological and compositional factors control the organic surface wettability of shales, contributing to the optimization of CO₂ geological storage and enhanced gas recovery strategies.

Surfactants play a crucial role in tertiary oil recovery by reducing the interfacial tension between immiscible phases, altering surface wettability, and improving foam film stability. Oil reservoirs have high temperatures and high pressures, making it difficult and hazardous to conduct lab experiments. In this context, molecular dynamics (MD) simulation is a valuable tool for complementing experiments. It can effectively study the microscopic behaviors (such as diffusion, adsorption, and aggregation) of the surfactant molecules in the pore fluids and predict the thermodynamics and kinetics of these systems with a high degree of accuracy. MD simulation also overcomes the limitations of traditional experiments, which often lack the necessary temporal–spatial resolution. Comparing simulated results with experimental data can provide a comprehensive explanation from a microscopic standpoint. This article reviews the state-of-the-art MD simulations of surfactant adsorption and resulting interfacial properties at gas/oil–water interfaces. Initially, the article discusses interfacial properties and methods for evaluating surfactant-formed monolayers, considering variations in interfacial concentration, molecular structure of the surfactants, and synergistic effect of surfactant mixtures. Then, it covers methods for characterizing microstructure at various interfaces and the evolution process of the monolayers’ packing state as a function of interfacial concentration and the surfactants’ molecular structure. Next, it examines the interactions between surfactants and the aqueous phase, focusing on headgroup solvation and counterion condensation. Finally, it analyzes the influence of hydrophobic phase molecular composition on interactions between surfactants and the hydrophobic phase. This review deepened our understanding of the micro-level mechanisms of oil displacement by surfactants and is beneficial for screening and designing surfactants for oil field applications.

In this research, fully degradable elastomeric sealing materials were developed to enhance the environmental sustainability of oil and gas extraction. The modification of millable polyurethane rubber (MPU) with polyglycolic acid/hydrogenated nitrile butadiene rubber (PGA/HNBR) led to the synthesis of PGA@MPU/HNBR composite materials. The impact of varying monomer quantities on the mechanical properties, degradation behavior, degradation mechanisms, and thermal stability of these materials was investigated. Our findings illustrate that an increasing proportion of HNBR in the PGA@MPU/HNBR composite materials resulted in a decreased degradation rate. Simultaneously, higher HNBR content improved the thermal stability of the materials, while the inclusion of PGA reduced material hardness, rendering the composites more susceptible to swelling. At an HNBR content of 40 phr, MPU at 60 phr, and PGA at 6 phr, the composite material demonstrated the highest retention of mechanical properties at 31.3% following 168 h of hydrolysis at 100 °C. The degradation of the composite materials in 100 °C water primarily resulted from the hydrolysis of MPU’s ester groups, with HNBR remaining unaffected.

A CO₂/N₂-responsive emulsion provides milder reaction conditions, nontoxicity, and economic feasibility compared to other switchable surfactants. In this study, CO₂/N₂-responsive pickering emulsions were fabricated by using a compounded dispersion containing SiO₂ nanoparticles (NPs) and superamphiphiles as the emulsifying agents. The synergistic effects of the SiO₂ NPs and superamphiphiles significantly stabilized the emulsion at all of the tested concentrations and prevented complete phase separation of oil and water. The electrostatic interaction between the SiO₂ NPs and superamphiphiles was disrupted after bubbling with CO₂ for 30 s, resulting in the breaking of the emulsion. However, the dispersion recovered its interfacial activity after the introduction of N₂ and again emulsified the emulsion. This reversible switching behavior was validated through three consecutive cycles of bubbling CO₂/N₂. The protonation and deprotonation of the SiO₂ NPs and superamphiphiles in response to CO₂/N₂ facilitated reversible assembly and disassembly, which enabled the switching of the emulsions between inactive and active forms. The novel highly stable Pickering emulsions demonstrated rapid demulsification and emulsification in response to CO₂/N₂ and are promising for a wide range of applications.

With the increasing development of low-permeability reservoirs, the significance of conformance control treatment has risen considerably. To address the conflict between injectability and plugging performance, as well as to enhance the deep migration capacity of conformance control agents, preformed submicron crosslinked polymer coils (SCPCs) have been manufactured using aqueous solution dispersion polymerization. Fourier transform infrared and scanning electron microscopy were employed to examine the chemical structure and micromorphology, while particle size distribution, zeta potential, rheological, and filtration properties were analyzed. The effectiveness of conformance control was confirmed through the parallel core displacement. The effective particle size of SCPCs was at a submicron level (500~800 nm). SCPCs exhibit a transitional threshold concentration between gel and sol states (0.25 wt%~0.5 wt%). SCPCs can efficiently block the 1.2 μm microporous filter membrane. The filtration time is up to 67.8 min. SCPCs can improve the water absorption rate of lower permeability cores from 21.21% to 57.89% with a permeability difference of 5. Therefore, SCPCs have good injectability, plugging performance, and deep migration capacity and can be used for conformance control in low-permeability reservoirs.