Although, the effects of ultrasonic irradiation on multiphase flow through porous media have been studied in the past few decades, the physics of the acoustic interaction between fluid and rock is not yet well understood. Various mechanisms may be responsible for enhancing the flow of oil through porous media in the presence of an acoustic field. Capillary related mechanisms are peristaltic transport due to mechanical deformation of the pore walls, reduction of capillary forces due to the destruction of surface films generated across pore boundaries, coalescence of oil drops due to Bjerknes forces, oscillation and excitation of capillary trapped oil drops, forces generated by cavitating bubbles, and sonocapillary effects. Insight into the physical principles governing the mobilization of oil by ultrasonic waves is vital for developing and implementing novel techniques of oil extraction. This paper aims at identifying and analyzing the influence of high-frequency, high-intensity ultrasonic radiation on capillary imbibition. Laboratory experiments were performed using cylindrical Berea sandstone and Indiana limestone samples with all sides (quasi-co-current imbibition), and only one side (counter-current imbibition) contacting with the aqueous phase. The oil saturated cores were placed in an ultrasonic bath, and brought into contact with the aqueous phase. The recovery rate due to capillary imbibition was monitored against time. Air-water, mineral oil-brine, mineral oil-surfactant solution and mineral oil-polymer solution experiments were run each exploring a separate physical process governing acoustic stimulation. Water-air imbibition tests isolate the effect of ultrasound on wettability, capillarity and density, while oil-brine imbibition experiments help outline the ultrasonic effect on viscosity and interfacial interaction between oil, rock and aqueous phase. We find that ultrasonic irradiation enhances capillary imbibition recovery of oil for various fluid pairs, and that such process is dependent on the interfacial tension and density of the fluids. Although more evidence is needed, some runs hint that wettability was not altered substantially under ultrasound. Preliminary analysis of the imbibition recoveries also suggests that ultrasound enhances surfactant solubility and reduce surfactant adsorption onto the rock matrix. Additionally, counter-current experiments involving kerosene and brine in epoxy coated Berea sandstone showed a dramatic decline in recovery. Therefore, the effectiveness of any ultrasonic application may strongly depend on the nature of interaction type, i.e., co-or counter-current flow. A modified form of an exponential model was employed to fit the recovery curves in an attempt to quantify the factors causing the incremental recovery by ultrasonic waves for different fluid pairs and rock types.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractInsight into the physical principles governing the mobilization of oil by ultrasonic waves is vital for developing novel techniques of oil extraction. Various mechanisms such as peristaltic transport due to mechanical deformation of the pore walls, reduction of capillary forces due to the destruction of surface films, coalescence of oil drops due to the Bjerknes forces, oscillation and excitation of capillary trapped oil drops, forces generated by cavitating bubbles, and sonocapillary effects may be responsible for enhancing the flow of oil through porous media in the presence of an acoustic field.This paper aims at analyzing the influence of highfrequency, high-intensity ultrasonic radiation on the immiscible and miscible displacement in porous media. Capillary imbibition (co-and counter current) and viscous displacement (Hele-Shaw) experiments were performed with and without ultrasonic waves.We observed that the increase in ultimate recovery is more pronounced than the increase in recovery rate when ultrasonic waves were applied in capillary imbibition experiments.The cases yielding enhancements on displacement efficiency (higher recovery rate and lower residual oil saturation) due to ultrasonic effects were identified.To analyze the viscous displacement under ultrasonic waves, experiments were performed on Hele-Shaw models. Immiscible (for mineral oil-brine and mineral oil-surfactant pairs) and miscible (for mineral oil-pentane, mineral oilkerosene and mineral oil -2-Propanol pairs) displacement experiments were performed. Changes on the displacement fronts and patterns were observed under ultrasound. Fractal techniques were used to analyze the changes and correlate them to the intensity of ultrasonic waves.

The effect of ultrasound on flow through a capillary using the pendant drop method was investigated. Water was injected into a 0.1 mm Hastelloy C-276 capillary tube submersed into several mineral oils with different viscosity, and kerosene. The average drop rate per minute was measured at several ultrasonic intensities. We observed that there exists a peak drop rate at a characteristic intensity, which strongly depends on oil viscosity and the interfacial tension between water and the oil. The semi-quantitative results reveal that the remarkable change in the interfacial forces between oil and water could be the explanation to the enhancement of oil recovery when the ultrasonic waves are applied.