Acoustic Stimulation for Enhanced Oil Recovery: A Review and Future Directions

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Constrained by the exhausted conventional oil and gas reservoirs and increasing world demand for energy, enhanced oil recovery (EOR) plays an important role in increasing hydrocarbon recovery from wells in maturing fields. As a physical enhanced oil recovery technology, acoustic stimulation-enhanced oil recovery is a new enhanced oil recovery technology that provides a nonthermal and light-chemical way to improve oil recovery. The advances of in situ acoustic stimulation of EOR, including the main types of recovery mechanisms, laboratory tests, numerical simulation, and field applications, have been summarized in this review. It is recognized that the improved recovery might be related to the viscosity reduction, wettability modification, interfacial tension between oil and water reduction, permeability enhancement, and mobilization of oil droplets by emulsification. Laboratory experiments shows that alone, the ultrasonic crude oil viscosity reduction rate could reach 20%–86%, while combined with chemical viscosity reducers, the viscosity reducer rate can reach 96.9%; ultrasound could reduce rock-fluid contact angle 64.73% increasing the wettability of rock and restore the permeability of low-permeability core and reached 80%–100%; field applications show that the increases of oil production rate were 50%–112% and the reduction of water cut was 4%–20%. Although laboratory research shows strong recovery potential, field applications are hindered by wellbore uncertainties, energy decay (high-frequency waves can only reach near the wellbore, and low-frequency waves cannot concentrate enough energy in the same place), reservoir complexity resulting in inefficient targeting of energy, and economics. Furthermore, the absence of a consistent quantitative relationship connecting the pore-scale to reservoir-scale performance further complicates its parameter optimization. The waveform optimization, advanced downhole tools, intelligent monitoring, and multiscale modeling with artificial intelligence are the future research directions that would lead to an accurate and efficient deployment. This summary demonstrated the great scope of acoustic stimulation EOR as a sustainable and noninvasive EOR technology, which was very informative for its large-scale expansion in complex reservoirs.