Effects of Asphaltene Concentration and Test Temperature on the Stability of Water-in-Model Waxy Crude Oil Emulsions

Abstract

In oil fields, the formation of water-in-waxy crude oil emulsion is inevitable. The dissolved/crystallized state wax can interact with asphaltenes and then greatly affect the emulsion stability. However, studies on this aspect are still insufficient. In this work, the effects of the test temperature (30 °C well above the wax appearance temperature (WAT) and 15 °C well below the WAT) and asphaltene concentration (0∼1.5 wt %) on the stability of the water-in-model waxy crude oil emulsions containing 10 wt % wax were systematically investigated. When the model crude oils contain no wax, the flowability of the oils is good and the asphaltene concentration has little influence on the oil rheology. Increasing the asphaltene concentration facilitates the adsorption of asphaltenes to the oil–water interface, thus reducing the interfacial tension and water droplet size while enhancing the interfacial dilatational modulus. The stability of the emulsions improves with the increase in the asphaltene concentration, but the emulsions are still unstable. When the model crude oils contain 10 wt % wax, the WAT slightly decreases from the initial 25 to 24 °C after the addition of asphaltenes. The oil rheology is greatly improved by the addition of 0.05 wt % asphaltenes. With the further increase of the asphaltene concentration, the improved rheological ability of the asphaltenes deteriorates rapidly. At the asphaltene concentration of 1.5 wt %, the oil rheology is dramatically aggravated. The stability of the emulsion containing 10 wt % wax is mainly controlled by two aspects: on the one hand, the dissolved-state wax (30 °C) could facilitate the adsorption of asphaltenes to the interface, further reduce the interfacial tension and the water droplet size, and enhance the interfacial dilatational modulus; on the other hand, the wax crystals precipitated in the oil phase (15 °C) can form a stronger network structure at relatively high asphaltene concentrations (0.5∼1.5 wt %) and then immobilize the water droplets. The above two aspects greatly improve the sedimentation and coalescence stabilities of the emulsions at 15 °C. In addition, we did not find persuasive evidence showing that the wax could crystallize around the water droplets and strengthen the oil–water interfacial films.

Theoretical Interpretation of pH and Salinity Effect on Oil-in-Water Emulsion Stability Based on Interfacial Chemistry and Implications for Produced Water Demulsification

“…Consequently, depicting emulsion formation and stabilization has received the attention of operators [154]. Considering that emulsification can be naturally associated with the surface active components of crude oils, the identification of asphaltene contents through characterization has been used to determine emulsion formation potential [155,156]. Also, research findings in the area of emulsion demulsification and the dosage of demulsifier required have been published [157,158].…”

Impact of the Temperature, Homogenization Condition, and Oil Property on the Formation and Stability of Crude Oil Emulsion

“…4 Therefore, it is imperative to gain a comprehensive understanding of crude oil emulsion formation and stability to address the challenges posed by emulsification in the petroleum industry. 5 Various types of crude oil emulsions, including water-in-oil (W/O), oil-in-water (O/W), water-in-oil-in-water (W/O/W), and oil-in-water-in-oil (O/W/O) emulsions, can be found in oilfields. 4 Among them, the W/O emulsion, often referred to as "chocolate mousse", poses the most common and challenging issue in the petroleum industry.…”

“…The consequences of emulsification in the petroleum industry are far-reaching, including a decrease in oil quality, higher transportation costs, catalyst poisoning in refineries downstream, and corrosion of facilities, pipelines, and tanks. ,, This not only escalates production costs but also reduces the yield of valuable crude oil . Therefore, it is imperative to gain a comprehensive understanding of crude oil emulsion formation and stability to address the challenges posed by emulsification in the petroleum industry …”

“…Undesirable emulsification has become a critical issue in the petroleum industry. − Crude oil emulsions are encountered during the initial stages of the oil recovery process . Even in low-salinity water flooding (LSWF), a popular method for enhanced oil recovery (EOR) in recent years, emulsion formation can pose challenges as a result of aqueous-phase injection. , Emulsification occurs during oil transportation, processing, and storage as well. , Emulsions, with their larger particle sizes compared to oil or water, can obstruct porous media in reservoirs, leading to inefficient displacement and reduced oil recovery. , The increase in viscosity induced by added water in emulsions can result in elevated pressure drops .…”

“…1−4 Crude oil emulsions are encountered during the initial stages of the oil recovery process. 5 Even in low-salinity water flooding (LSWF), a popular method for enhanced oil recovery (EOR) in recent years, emulsion formation can pose challenges as a result of aqueous-phase injection. 6,7 Emulsification occurs during oil transportation, processing, and storage as well.…”