RESUMO
In order to meet the requirements of tertiary oil recovery technology in a low-permeability, dense, and high-salt reservoir, gaseous SiO2 nanoparticles were modified with trichloro(octyl)silane and aminopropyl triethoxysilane by interface protection modification, and amphiphilic Janus-SiO2 nanoparticles with hydrophobic carbon chain and hydrophilic amino group were prepared. The basic properties of amphiphilic nanoparticle dispersion were evaluated by surface interfacial tension and wettability tests, and the oil displacement effect of amphiphilic nanoparticle dispersion was investigated. The results show that the size distribution of Janus-SiO2 nanoparticles with n-octyl as the hydrophobic carbon chain and amino group as the hydrophilic headgroup is uniform, and they have good dispersion in mineralized water. The change of salinity has little effect on the interfacial activity. The interfacial tension between the amphiphilic nanoparticle dispersion and crude oil is always on the order of 10-2 mN/m, and the amphiphilic nanoparticle dispersion has good interfacial activity. Amphiphilic nanoparticles adsorbed on the rock surface can enhance the hydrophilicity of the rock surface. Amphiphilic nanoparticle dispersion liquid has a certain effect of improving oil recovery in the environment of high-salt and low-permeability reservoir. Under the condition of 65 °C and salinity of 8000 mg/L, injection of 0.5 PV 0.05% amphiphilic nanoparticle dispersion can enhance oil recovery by 14.6% on the basis of water flooding. The mechanism of amphiphilic nanoparticles to improve the recovery efficiency of low-permeability tight high-salt reservoir mainly includes reducing the oil-water interfacial tension, changing the rock wettability, and enhancing the shear viscosity of oil and water interface and the interfacial film strength, which has excellent potential application prospect in the development of low-permeability tight high-salt reservoir.
RESUMO
Produced gas re-injection is an effective and eco-friendly approach for enhancing oil recovery from shale oil reservoirs. However, the interactions between different gas phase components, and the oil phase and rocks are still unclear during the re-injection process. This study aims to investigate the potential of produced gas re-injection, particularly focusing on the effects of methane (CH4) content in the produced gas on shale oil displacement. Molecular dynamics simulations were employed to analyze the interactions between gas, oil, and matrix phases with different CH4 proportions (0%, 25%, 50%, and 100%), alkanes and under various burial depth. Results show that a 25% CH4 content in the produced gas achieves almost the same displacement effect as pure carbon dioxide (CO2) injection. However, when the CH4 content increases to 50% and 100%, the interaction between gas and quartz becomes insufficient to effectively isolate oil from quartz, causing only expansion and slight dispersion. Interestingly, the presence of CH4 has a synergistic effect on CO2, facilitating the diffusion of CO2 into the oil film. During the gas stripping process, CO2 is the main factor separating oil from quartz, while CH4 mainly contributes to oil expansion. In addition, for crude oil containing a large amount of light alkanes, extracting light components through mixed gas may be more effective than pure CO2. This study offers valuable insights for applications of produced gas re-injection to promote shale oil recovery.
