Preparation of Amphiphilic Janus-SiO2 Nanoparticles and Evaluation of the Oil Displacement Effect.

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.

Evaluation of the Driving Effect of the CO2 Viscosity Enhancer Composite System in Extra-Low Permeability Sandstone Reservoirs.

CO2 flooding is an important technology to enhance oil recovery and realize effective storage of CO2 in ultra-low permeability reservoir. However, due to poor reservoir properties, strong interlayer heterogeneity, and unfavorable mobility ratio of CO2, gas channeling easily occurs, resulting in low recovery. Chemically assisted CO2 thickening technology has been developed to control the gas flow rate and improve the CO2 repulsion effect. Through solubility and viscosity enhancement tests, the CO2 viscosity enhancer composite system is preferably constructed and then combined with the core drive experiments, the effect of CO2 viscosity enhancer composite system on oil drive in homogeneous and non-homogeneous cores is evaluated, the correlation between the drive efficiency and viscosity enhancement and solubility of the system is analyzed, and the mechanism of recovery enhancement is explored. The results show that the preferably constructed CO2-ASA-LAP composite system has a good effect for improving the gas drive effect under simulated formation conditions, and its improvement effect is positively related to the solubility and viscosity increase of the system. Combining oil repelling efficiency and economic considerations, ASA:LAP = 1:1 is selected as the optimal CO2 viscosity enhancer composite oil repelling system. For homogeneous cores, the CO2-ASA-LAP combined system drive can increase the recovery rate by 6.65% as compared with CO2 flooding. For heterogeneous cores, when the permeability difference is 5, the comprehensive recovery factor of the CO2-ASA-LAP system flooding is 8.14% higher than that of CO2 flooding. When the permeability difference increases from 5 to 10, the comprehensive recovery factor of the CO2-ASA-LAP system flooding increases by 1.85%.The injection of the CO2-ASA-LAP system has some injurious effect on the permeability of the reservoir core, and the smaller the permeability, the greater the degree of injury. The mechanism of the CO2-ASA-LAP system to improve recovery includes increasing CO2 viscosity, improving the oil repelling flow ratio, blocking high seepage channels, initiating low seepage residual oil, enhancing CO2 dissolution, and expanding the oil repelling effect.

CO2-Low Interfacial Tension Viscoelastic Fluid Synergistic Flooding in Tight Reservoirs.

Tight oil reservoirs have poor physical properties, insufficient formation energy, and low natural productivity. CO2 flooding is an important technical mean that enhances the oil recovery of dense reservoirs and achieves effective CO2 sequestration, but strong heterogeneity of the tight oil reservoir usually results in gas channeling and poor enhanced oil recovery effect. The existing methods to prevent gas channeling are mainly to use the small-molecule amine system and the polymer gel system to plug fracture and high permeability channels. The small-molecular amine system has low flash points and pollutes the environment and the polymer gel has poor injectivity and great damage to the formation, which limit their large-scale application. Therefore, a new viewpoint of CO2-low interfacial tension viscoelastic fluid synergistic flooding for enhanced oil recovery in a tight oil reservoir was made. The performance of low interfacial tension viscoelastic fluid (GOBT) was studied. The injectivity and oil displacement effect of CO2-GOBT synergistic flooding were evaluated, and the mechanism of CO2-GOBT synergistic flooding was discussed. The experimental results showed that 0.4% GOBT is a low interfacial tension viscoelastic fluid, which has strong adaptability to the salinity water of tight oil reservoirs (6788-80,000 mg/L), good viscosity stability at different pHs, excellent capacity to emulsify crude oil, and the ability to improve reservoir water wettability. CO2 alternating 0.4% GOBT flooding has good injection ability in cores (K a = 0.249 mD), and injecting 0.4% GOBT can effectively increase the injection pressure of subsequent CO2 flooding. CO2 alternating 0.4% GOBT flooding can effectively improve water flooding recovery in tight sandstone reservoirs, which is better than CO2 flooding and 0.4% GOBT flooding in both homogeneous and heterogeneous conditions. The mechanisms of CO2 alternating 0.4% GOBT flooding to enhance the oil recovery include that GOBT and CO2 foam block high permeability layers, shunt and sweep low permeability layers, and GOBT emulsify and wash oil. CO2 partially dissolving in GOBT synergistically enhances the core water wettability, which improves GOBT injectability, emulsification, and stripping ability to residual oil.