Isothermal CO₂ injection into water-saturated porous media: Lattice-Boltzmann modelling of pulsatile flow with porosity, tortuosity, and optimal frequency characterization

The Lattice Boltzmann Method (LBM) is used to simulate the isothermal injection of CO₂ into a water-saturated, homogeneous porous medium. The complex multiphase flow is modeled using the 2D-pseudopotential Shan-Chen multiphase LBM. This work proposes a unique fluid-pulse technology similar to the one applied to enhance oil recovery with CO₂ sequestration. This technology is different from classical CO₂ sequestration in aquifers and, to our knowledge, has never been used before. The primary purpose is to investigate whether our LBM simulation allows the introduction of fluid-pulse CO₂ injection patterns similar to those reported in the literature on hydrocarbon reservoirs and to evaluate the benefit of using such a technique compared to classical uniform injection. First, our simulations consider a transient homogeneous flow with uniform inlet velocity to determine the natural frequency of the instabilities triggered downstream of the interstitial pore array. Then, CO₂ is injected at the inlet in a pulsating regime, varying the forcing frequency near and far from the natural frequency to determine its effect on CO₂ penetration. Results demonstrate that a pulsatile injection effectively enhances CO₂ sequestration in aquifers when forced with a characteristic frequency. However, this frequency resulting after CO₂ is injected to displace the water differed from the natural frequency preliminarily obtained from the homogeneous water flow. Injecting at the characteristic frequency has proven an effective technique for boosting CO₂ penetration into a water-saturated porous medium, with a significant enhancement estimated between 1.5 % and 16 % for a range of pulsatile amplitudes between 1 % and 10 %.