Maximization of oil mobility within a hydrocarbon reservoir for elastic wave-based enhanced oil recovery

Elastic wave-based enhanced oil recovery (EOR) has been proposed and used as a low-cost EOR method. Strong wave motions were reported to be able to mobilize oil still remaining in previously bypassed zones. This paper discusses the feasibility of inducing resonance-like wave motion within an oil reservoir in order to maximize wave-based EOR. To this end, a novel mathematical algorithm was developed to determine the optimal conditions of wave sources that can maximize the wave motion within an oil reservoir while minimizing, if desired, the vibrational disturbance in the neighboring formations. The optimized wave sources can generate strong wave motion within an oil reservoir, thereby potentially allowing the oil ganglia trapped in rock pores to overcome the strong capillarity between the droplets and the rock matrix. Numerical experiments were conducted to identify the unknown optimal time signal information of wave sources that can lead to the maximum kinetic energy or maximum acceleration within an oil reservoir. These numerical experiments consider realistic geometries and material properties of a hydrocarbon reservoir, as well as multiple wave sources located on the ground surface. We demonstrate that optimized time signals can result in constructive interference of wave motion within a targeted hydrocarbon reservoir. We show that such signals can be either monochromatic, where the excitation frequency corresponds to one of the discrete reservoir amplification frequencies, or can even be transient. Overall, when the formation's characteristics are known, our method allows one to prescribe the necessary waveforms that maximize particle motion within the reservoir.