Numerical analysis of dispersion, attenuation, and seismic effects in a porous rock saturated with three-phase immiscible fluids

Abstract

Multiphase flow in porous rock is of great importance in the application of many industrial processes, including reservoir delineation, enhanced oil recovery, and CO₂ sequestration. However, previous research typically investigated the dispersive behaviors when rock saturated with single or two-phase fluids and conducted limited studies on three-phase immiscible fluids. This study investigated the seismic dispersion, attenuation, and reflection features of seismic waves in three-phase immiscible fluid-saturated porous rocks. First, we proposed the calculation formulas of effective fluid modulus and effective fluid viscosity of multiphase immiscible fluids by taking into account the capillary pressure, reservoir wettability, and relative permeability simultaneously. Then, we analysed the frequency-dependent behaviors of three-phase immiscible fluid-saturated porous rock under different fluid proportion cases using the Chapman multi-scale model. Next, the seismic responses are analysed using a four-layer model. The results indicate that the relative permeability, capillary pressure parameter, and fluid proportions are all significantly affect dispersion and attenuation. Comparative analyses demonstrate that dispersion and attenuation can be observed within the frequency range of seismic exploration for a lower capillary parameter α₃ and higher oil content. Seismic responses reveal that the reflection features, such as travel time, seismic amplitude, and waveform of the bottom reflections of saturated rock and their underlying reflections are significantly dependent on fluid proportions and capillary parameters. For validation, the numerical results are further verified using the log data and real seismic data. This numerical analysis helps to further understand the wave propagation characteristics for a porous rock saturated with multiphase immiscible fluids.