In this article, experiments and simulations were conducted to evaluate performance of surfactant-nanoparticles foam for enhanced oil recovery under high temperature. Experimentally, the displacement behavior of surfactant-nanoparticles foam for enhanced oil recovery was studied by micromodel tests at 90 °C. The recovery performance of surfactant-nanoparticles foam flooding was analyzed by sandpack flooding experiments at 150 °C. Theoretically, a mechanistic model of surfactant-nanoparticles foam flooding was constructed. The micromodel tests indicate that the surfactant-nanoparticles foam was more stable than that of the surfactant foam in the porous media at 90 °C. The surfactant-nanoparticles foam could accumulated in the pores with less oil and increase the swept area. The crude oil could be emulsified into oil droplets by surfactant-nanoparticles foam which can greatly enhance the oil recovery. The sandpack flooding results show that the surfactant-nanoparticles foam had better recovery performance at 150 °C. Compared with the surfactant foam, the surfactant-nanoparticles foam produced from the sandpack flooding experiment had a smaller average particle size and higher sphericity. A mechanistic model of surfactant-nanoparticles foam flooding was constructed. A good match was achieved between the numerical simulation and sandpack flooding experiments in terms of pressure and oil recovery by adjusting the model parameters. The simulation study indicates that the performance of surfactant-nanoparticles foam flooding is better than that obtained by surfactant foam flooding under high temperature.
Summary Cyclic in-situ combustion (ISC) is a novel process with great potential for thermal enhanced oil recovery (EOR). In this study, a 3D physical simulation experiment of cyclic ISC after cyclic steam stimulation (CSS) was carried out for the first time. The mass loss during heavy oil oxidation was studied by thermogravimetry (TG) and the preheating temperature of sandpack was determined by differential scanning calorimeter (DSC). The oxidation process of heavy oil in a porous medium was investigated by a heavy oil static oxidation experiment. The development characteristics and EOR mechanism of cyclic ISC after CSS were studied through 3D physical simulation experiments and the characteristics of the coking zone was studied by scanning electron microscope (SEM) and computed tomography (CT). The results of the thermal analysis indicate that three different regions were observed with increasing temperature: low-temperature oxidation zone (LTO), fuel deposition zone (FD), and high-temperature oxidation zone (HTO). When the temperature reaches 480°C, the mixed oil sand has the most exothermic effect and the high-temperature oxidation reaction is the most vigorous. The results of the 3D physical simulation show that steam channeling and steam overlay in CSS reduced the swept volume of steam and heat usage rate. During the cyclic ISC, the oil bank can overcome the heterogeneity of the oil reservoir caused by steam channeling and steam overlay, which makes the combustion front move forward smoothly. Cyclic ISC can greatly increase the temperature of the zone near the well, and upgrade the crude oil through cracking to reduce the viscosity of heavy oil. The foaming oil formed by the dissolution of flue gas improves the fluidity of the crude oil. The oil recovery of CSS is 19.3%, and the oil recovery of cyclic ISC increased by 13.2%. SEM and CT show that flake black solid coke was attached to the surface of the sand at the coking zone. The coking zone is a porous medium structure with a porosity of 35.14%, which has little effect on the oil recovery in the process of cyclic ISC.
An emulsion is a dispersion with a complex mechanism of formation and a poor stability. In the preparation of emulsions, the used surfactant concentration, oil−water ratio, and kinetic conditions affect the type, microscopic characteristics, and rheological properties of the emulsions. As a result of its high viscosity, it is difficult to disperse the heavy oil with mechanical agitation, and the stability of the emulsion system formed is poor; hence, it is challenging to study its rheological properties. Therefore, herein, the ultrasonic dispersion method was employed to prepare the emulsion, and the microscopic characteristics of the emulsion were observed using an optical microscope and nanoparticle size analyzer. The conductivity of the emulsion system was studied by a conductivity meter. The effects of different surfactant concentrations, oil−water ratios, and kinetic conditions on the emulsion type and micro-characteristics were obtained. The experiments were performed to study the rheological properties of oilin-water (O/W) and water-in-oil (W/O) emulsions. The results indicate that the emulsion prepared using an ultrasonic dispersion method was O/W-type when the mass percentage of a surfactant solution was higher than 0.1 wt % and the oil−water ratio was less than 1:3. The droplet size reaches a nanometer level and increases with a higher surfactant concentration. The particle size no longer decreases when the critical micelle concentration of the surfactant is reached. The droplet size corresponding to the peak of size frequency distribution was 70 nm, and the rheological curve was a shear-thickening dilatant fluid. When the mass percentage of a surfactant solution was lower than 0.1 wt % and the oil−water ratio was higher than 1, a W/O emulsion was formed with the droplet size of 10 μm. When the shear rate was less than 50 s −1 , the emulsion was a pseudo-plastic fluid with shear-thinning behavior. As the shear rate increased, the emulsion gradually exhibited Newtonian fluid behavior.
Summary The expansion of the steam chamber is very important for the recovery performance of steamflooding. In this paper, we discuss 1D and 2D sandpack experiments to performed analyze the effect of flue gas on steam chamber expansion and displacement efficiency in steamflooding. In addition, we examine the effect of flue gas acting on the steam condensation characteristics. The results show that within a certain range of injection rate, flue gas can significantly enlarge the swept volume and oil displacement efficiency of steam. However, when the flue gas injection rate is excessively high (the ratio of gas injection rate to steam injection rate exceeds 4), gas channels may form, resulting in a decline of oil recovery from steamflooding. The results of the 2D visualization experiments reveal that the swept volume of the steam chamber during steamflooding was small, and the remaining oil saturation in the reservoir was high, so the recovery was only 28%. The swept volume of the steam chamber for flue-gas-assisted steamflooding was obviously larger than that of steamflooding, and the recovery of flue-gas-assisted steamflooding in 2D experiments could reach 40.35%. The results of the steam condensation experiment indicate that flue gas could reduce the growth and coalescence rates of steam-condensed droplets on the cooling wall and increase the shedding period of the droplets. Macroscopically, flue gas could reduce the heat exchange rate between the steam and the reservoir and inhibit the rapid condensation and heat exchange of the steam near the injection well. As a result, flue gas could expand the steam chamber into the reservoir for heating and displacing oil.
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