An ultrasonic irradiation technique for treatment of asphaltene deposition

Abstract

The need for better understanding of asphaltene behavior in the crude oil and treatment techniques of its deposition in porous medium has been recognized but still requires extensive research and experimental activities. The ambitious goals of this study are to investigate (1) influences of using ultrasonic irradiation on asphaltene behavior in the UAE crude oil, with consideration of solvent and temperature effects and (2) influences of ultrasonic irradiation characteristics such as frequency and time interval on damaged oil permeability (due to asphaltene deposition) of carbonate reservoir rocks. To achieve the abovementioned goals, three groups of experiments using ultrasonic irradiation were carried out. In the first group, 18 identical crude oil samples of 2.47 wt.% initial asphaltene content were subjected to different time intervals of ultrasonic irradiation of 0, 5, 10, 15, 25 and 30 min and under different temperatures of 25, 40 and 60 °C, respectively. Oil viscosity was measured, and microscopic images of the centrifugated oil samples of asphaltene clusters were obtained. In the second set of experiments, 12 identical crude oil samples with different toluene concentrations of 5, 10, and 15 vol.% were subjected to four different durations of ultrasonic irradiation and under different temperatures. In the third group, seven actual carbonate core samples of damaged oil permeability due to the injection of 60 pore volumes of asphaltic crude oil were subjected to different ultrasonic time interval of 5, 10, 15, 20, and 25 min and frequencies of 10, 15 and 20 kHz, respectively. Both the oil permeability of these samples measured and the scanning electron microscope (SEM) images were carried out before and after ultrasonic irradiation treatment. The results showed that subjection of the UAE crude oil to ultrasonic irradiation decreases the size of asphaltene clusters. Consequently, this effect reduces asphaltene tendency to precipitate at 10 min or more time interval of ultrasonic irradiation. In addition, similar results were obtained with solvent effect, but with more reduction in oil viscosity. The results also indicated that the increase of ultrasonic time interval and/or frequency drastically improve(s) damaged oil permeability.