Nice work. Unsteady injection is indeed very interesting. I remember research on pulsed CO2 injection for recovery at Shell Research in early 1980's (L.de Jong ). The idea was that fast injection would promote fingering and because of this mixing.

Production would occur through the injection injection well after allowing time for mixing of the CO2 with the crude. Basically fast injection inducing fingering can if the injection is followed by a rest period to allow mixing can "stabilize" the contact front between C02 and the reservoir fluid. In case of injection in an aquifer, this will be less efficient than for oil, because the miscibility of CO2 and brine is limited. I therefore think that the CO2 sequestration problem is quite different from the enhanced oil recovery.

Thanks for your comment, Avraham. Your experience in EOR is valuable in understanding the challenges of pulsatile CO2 injection. In our case, we are focusing on water displacement and assuming a minimal mixing with the injected CO2. Thus, what we found in such conditions, as it happens in other complex dynamic systems, is that there is a characteristic frequency for which the displacement (without mixing) can be eased in up to 16% for the same injected time (less resistance from the saturated aquifer, assuming the water can be displaced elsewhere downstream). It is a theoretical work (based on CFD simulation), but I expect this brings some light to field engineers designing CO2 injection systems to envision new manners of enhancing (with less energy and less cost) the CO2 sequestration. Thanks for your feedback. It´s very appreciated!!

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

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https://doi.org/10.1016/j.tsep.2023.101949Get rights and content

Abstract

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 %.