Effect of Subsurface Microseisms on the Motion of Dispersed Droplets in Pores

Abstract

Human-induced seismicity has drawn substantial attention in recent years. The effect of seismicity on subsurface structures has been studied extensively. However, the effect of seismicity, especially microseismicity, on surrounding immiscible fluids is rarely investigated. In porous media with two or more immiscible fluids, different amplitudes of vibration induced by seismicity have distinct effects on the dynamic behavior of the fluids. Three types of pore-scale models are prevalent for analyzing the motion of immiscible droplets. The underlying assumptions and accuracy of these models are compared in this study in both the frequency and time domains. The frequency domain analysis shows that resonance can be addressed in all three of the models; the frequency response curves, however, present significant differences, which are attributed to the missing physics considered in some models. Time domain analysis is performed in both small-amplitude and large-amplitude oscillation. The nonlinearity in large-amplitude oscillation is attributed to the constricted geometry of the capillary tube. Although the term "large-amplitude" is used in this study, the corresponding amplitude is still within the amplitude range of microseisms. The momentum balance model is identified as the most accurate oscillatory model so far in comparison with computational fluid dynamics simulations. In addition, the potential approach to incorporate this pore-scale model in seismic wave attenuation analysis is found to be possible. The frequency correction function and structural factor are calculated to embed the momentum balance model into Biot's poroelastic model. The resonance of the dispersed phase can also be addressed theoretically in porous media of random packed spheres.