Using acoustic energy in enhanced oil recovery is not a new idea but yet is categorized as an unconventional method. In previous studies at our institution, the effect of ultrasonic radiation on capillary imbibition recovery of light oil from a water wet medium was widely investigated. Upon promising results, the study was extended to more challenging cases such as oil wet matrix (with and without initial water) and heavy oil. The effects of ultrasonic intensity and frequency were also included.

Cylindrical sandstone cores were placed into imbibition cells where they contacted with aqueous phase. Each experiment was run with and without ultrasonic radiation keeping all other conditions and parameters constant. The experiments were designed to investigate how the presence of initial water saturation can affect the recovery (Swi=0 to 40%), and also how the recovery changes for different oil viscosities (35 to 1600 cp). Furthermore, the samples were tendered oil-wet by treating with dryfilm to quantify the effects of wettability. In addition, the specifications of acoustic source such as ultrasonic intensity (45 to 84 W/ sq cm) and frequency (22 and 40 kHz) were also changed. An increase in recovery was observed with ultrasonic energy in all cases. This change was more remarkable for oil-wet medium. The additional recovery with ultrasonic energy became lower as the oil viscosity increased.

The results revealed that the ultrasonic intensity and frequency are very critical on the performance. This is a critical issue as the ultrasonic waves have limited penetration into porous medium and the intensity reduces while penetrating into porous medium. This is a major drawback in commercializing this promising process for well stimulation. Hence, we designed a set-up to measure the ultrasonic energy penetration capacity in different media, namely air, water, and slurry (sand+water mixture). A one-meter long water or slurry filled medium was prepared and the ultrasonic intensity and frequency were monitored as a function of distance from the source. The imbibition cells were placed at certain distances from the sources and the oil recovery was recorded. Then, the imbibition recovery was related to the ultrasonic intensity, frequency, and distance from the ultrasonic source.

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