Abstract
Under the conditions of thermal oil recovery, the heavy oil in a reservoir usually exists in the form of W/O emulsion with high water content, which has significant effect on oil recovery performance. The most important parameter on the stability of W/O emulsion is interfacial properties. Thus, in order to investigate the effect of interfacial properties on the stability of W/O emulsion in a heavy oil reservoir at elevated temperatures, experiments have been conducted to generate various emulsions with variations in the temperature; stirring rate; contents of asphaltene, resin, and wax of the simulated heavy oil; and water salinity based on a target heavy oil reservoir in China. Then, the properties of the W/O emulsions include viscosity, interfacial viscosity (IFV), interfacial tension (IFT), and dehydration rate; the microscopic morphologies are measured as well. The experimental results show evidently stable W/O emulsion of heavy oil and water generated in thermal processes due to the stable, thick, and indistinct interface between heavy oil and water, where the active molecules of asphaltene and resin are accumulated. The interface connects the central large droplet and the surrounding small droplets tightly. The results also indicate the size of the central droplet, and the indistinct interface can be enlarged with increasing temperature and increasing stirring rate. Compared to resin, it is noted that the larger asphaltene molecules have stronger connection because of their stronger intermolecular force, larger IFV, and less IFT. At the same time, the stability of W/O emulsion will be strengthened with increasing temperature and stirring rate and gradually weakened with increasing salinity. In conclusion, the stability of water in heavy oil emulsion is mainly related to the large interfacial viscosity of the interface with much more heavy components such as asphaltene and resin compared to thin oil.
Highlights
More than half of the proven oil reserves in the Bohai Oilfield are heavy oil with viscosity over 150 mPa·s, and the depth of the reservoirs usually ranges from 1000 m to 1500 m
The production rates of the heavy oil wells with viscosity of 350 mPa·s-1000 mPa·s were significantly increased by thermal processes, such as cyclic steam stimulation and cyclic steam and gas stimulation, and more than 50 m3/d oil production rate was obtained compared to the rate of below 20 m3/d by primary cold production
In order to investigate the effect of interfacial properties on the stability of heavy oil emulsion in thermal processes, various emulsions are generated to simulate heavy oil and water under different temperatures; stirring rates; contents of asphaltene, resin, and wax of the simulated heavy oil; and water salinities based on a real reservoir
Summary
More than half of the proven oil reserves in the Bohai Oilfield are heavy oil with viscosity over 150 mPa·s, and the depth of the reservoirs usually ranges from 1000 m to 1500 m. The heavy oil is produced to surface in the form of stable W/O emulsion in thermal recovery processes such as steam injection [1,2,3]. The active oil components at the water-oil interface are decisive for the stability of the heavy oil emulsion, and water release rates are decreased when large contents of asphaltene and resin are found in oil [11]. In order to investigate the effect of interfacial properties on the stability of heavy oil emulsion in thermal processes, various emulsions are generated to simulate heavy oil and water under different temperatures; stirring rates; contents of asphaltene, resin, and wax of the simulated heavy oil; and water salinities based on a real reservoir. Based on the measurement results, the effect of interfacial properties of water and heavy oil on emulsion stability is discussed in detail
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