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 ShanChen 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 %.