Surfactants play an important role in enhancing oil recovery (EOR). With the development of tertiary oil recovery technology and the continuous improvement of environmental protection requirements, green environmentally friendly surfactants play an important role in replacing conventional surfactants. In this paper, cardanol polyoxyethylene ether (CPE) was synthesized from natural biomass cardanol. Its structure was characterized, and its surface/interface properties, salt and temperature resistance, wettability, emulsification, and oil displacement effect were studied experimentally. The results showed that CPE had good interfacial activity and temperature and salt tolerance, which can reduce the oil-water interfacial tension to 10^-1 mN/m. The emulsion formed by CPE had good stability. With the increase in CPE dosage, the droplet size of the emulsion decreases. The emulsion stabilized by CPE can effectively enhance oil recovery by 11.8%. Therefore, CPE not only is environmentally friendly but also has great application potential in the field of EOR.

At present, the research on aquathermolysis catalysts mainly focuses on the catalytic effect of external catalysts on the reaction, ignoring the fact that external catalysts will form complexes with in situ inorganic minerals after entering the reservoir. In this paper, we investigated the effects of transition metal complexes as external catalysts and bentonite as in situ catalysts on aquathermolysis, respectively. Meanwhile, the aquathermolysis reaction co-catalyzed by external and in situ catalysts was further investigated. The results show that the transition metal complexes exhibited good co-catalysis with bentonite. The viscosity reduction rate can reach 73.47% at 200 °C and 4 h with 0.1 wt.% of catalyst (NAD–Zn) addition. The addition of ethanol under the same reaction conditions will further increase the viscosity reduction rate to 84.59%. The results of thermogravimetric analysis, component analysis and boiling range analysis of heavy oil show that the heavy components in heavy oil are cracked into light components after the aquathermolysis. The results of elemental analysis show that the heteroatoms in the heavy oil were removed and the quality of the crude oil was improved. The results of GC–MS analysis of the model compounds showed that the process of aquathermolysis was mainly through the cleavage of C–C, C–N and C–S bonds to crack the macromolecules into small molecules, and then achieve the effect of viscosity reduction. The main mechanism of catalyst action is the acidic center on the surface of the bentonite and the coordination bonds formed by the transition metal complexes with the heteroatoms.

Clathrate hydrates are ice-like compounds consisting of small gas molecules enclosed in water molecule cages. The formation of gas hydrate in oil and gas pipelines may result in flow assurance failure and serious safety and environmental concerns. Antiagglomeration is a promising method to mitigate gas hydrate risks in hydrocarbon flowlines. Morphological behavior of hydrates in the presence of antiagglomerants can provide important information on the antiagglomeration mechanisms. This study reports the visual observations of the morphology of hydrate formed with a water droplet immersed in cyclopentane with and without the presence of a hydrate antiagglomerant (AA). The effect of AA on the hydrate crystal growth was investigated. The AA exhibited a kinetic inhibition effect. With no AA, a faceted hydrate shell formed around the water droplet was observed. The subcooling can affect the rate of lateral growth. Higher subcooling facilitates hydrate growth. With the presence of 0.04 wt % AA, a hairy and porous morphology of hydrate was observed. At higher AA concentrations, a vertical type of growth after the lateral growth of the hydrate shell was observed. This is probably the first report of vertical growth of cyclopentane hydrate formed with a water droplet. A hypothesis is proposed to explain the vertical growth mechanism of the hydrate crystals.

In this paper, a betaine-based gel containing 2.0% erucamide propyl betaine (EAPB), 0.5% oleic acid amide propyl betaine (OAPB), and 0.1% KCl was prepared for use as a fracturing fluid. The performance evaluation showed that KCl may improve the temperature resistance and increase the viscosity of the optimized fracturing fluid. At 80 °C, the apparent viscosity of the viscoelastic surfactant (VES)-based fracturing fluid was approximately 50 mPa·s. Furthermore, the gel had high shear resistance, good viscosity stability, and high sand-carrying performance. After being sheared at 170 s⁻¹ for 60 min, the reduction in viscosity was 13.6%. The viscosity of the gel was relatively stable at room temperature (27 °C) for one week. In a suspension containing 10% sand (particle size < 0.45 mm, density = 2.75 g cm⁻³), the settling velocity of proppant particles was 1.15 cm h⁻¹. In addition, we detected that the critical micelle concentration of this gel was approximately 0.042 wt%. The viscosity could be reduced to <5 mPa·s at 60 °C within 1 h when 6.0% crude oil was present, and oil displacement experiments showed that the broken fracturing fluid can enhance the oil displacement rate up to 14.5%. This work may facilitate research on fracturing fluids and oil recovery.

In this study, the foaming properties of a compound surfactant formula containing cetyltrimethylammonium chloride (CTAC), cocamidopropyl betaine (CDAB), fatty alcohol polyoxyethylene ether-7 (AEO7) and sodium alpha-olefin sulfonate (AOST) were evaluated to meet the application requirements for foam generation and foam drainage in gas wells. The results exhibited that the foaming volume and the half-life of the compound surfactant solution (0.05 wt % CTAC + 0.7 wt % CDAB + 0.6 wt % AEO7 + 0.05 wt % AOST) can reach the values of 550 mL and 23 min, respectively, which suggested that the foaming ability and stability were improved in comparison with each solution containing a single surfactant. It showed that the surface tension can be lowered to 22.4 mN/m with the presence of the compound surfactants. Simultaneously, the microstructure of the foam was observed using a polarizing microscope, and it was found that there were almost no polyhedron structures in the foam within a certain range of formula concentrations. The results of the experiments also clarify that the formula has well properties of temperature resistance and salt resistance (measured using a high-speed agitator).