Experimental study on pore-scale mechanisms of ultrasonic-assisted heavy oil recovery with solvent effects.

Production from heavy asphaltenic oil reservoirs poses several challenges that require new and innovative techniques for improved production and recovery. The main objective of this study is to experimentally investigate the influences of ultrasonic waves and solvent on oil viscosity, asphaltene precipitation behavior, and recovery of a heavy asphaltenic crude oil. This study is divided into two main parts. In the first part, crude oil samples were subjected to ultrasonic radiation with a frequency of 20 kHz and varying output powers (30, 60, and 100 W) for various durations. The viscosity of each oil sample was measured immediately after stopping ultrasonic radiation and also after 24 h of irradiation. An optimum time for ultrasound radiation was determined when the cooled-down radiated oil reached a minimum viscosity. We then measured the viscosity of the ultrasonically treated oil samples blended with a solvent (i.e., n-heptane) to assess the synergetic effect of ultrasonic radiation and solvation on the oil viscosity. In the second part, the application of ultrasonic radiation on the asphaltene aggregates and oil recovery was examined using solvent flooding in a transparent porous medium. Four sets of experiments were undertaken where the solvent was injected into the micromodel saturated with the untreated and ultrasonically treated oil free from or blended with the solvent. The results showed that ultrasonic treatment decreased the size of asphaltene aggregates and consequently reduced the viscosity of the crude oil. As a result, the suspension of asphaltene in the ultrasonically treated oil increased and reduced its tendency to precipitate at the optimum radiation time. Furthermore, the results indicated that the combined use of ultrasound and solvent had the greatest reduction in the oil viscosity compared to the untreated crude oil with ultrasonic waves or solvent. • The joint effect of ultrasonic radiation and solvent on viscosity and asphaltene aggregation of crude oil was investigated. • A synergy in viscosity reduction was found when the solvated crude oil was subjected to ultrasonic radiation. • The flooding tests showed that ultrasonic radiation locally decreased the size and precipitation of asphaltene aggregates. • The ultrasonicated oil was displaced more efficiently on the local pore space. • Considerably lower asphaltene precipitation was found when the radiated oil was displaced by the solvent. [ABSTRACT FROM AUTHOR]