Microscale Evaluation on the Feasibility of Foam-Assisted CO2 Sequestration in the Absence and Presence of Oleic Phase: An Integrated Microfluidic Experimental and Pore Network Modeling Study
Authors: Yang Jun , Zhao Jing , He Yanfeng , Zeng Fanhua 
Published: October 2023

Abstract
Gas channeling caused by unfavorable mobility ratio is one of the key issues that limits total storage efficiency of CO2 during geological sequestration. Foam-assisted CO2 sequestration technology is a promising game changer that significantly improves CO2 storage efficiency. The pore-scale process of foam-assisted CO2 sequestration, in the absence and presence of remaining oleic phase, is studied with microfluidic experiments, followed by the comparison with corresponding pore network model incorporated with pore filling event-based algorithm.
In this work, microfluidic investigation is carried out to study the pore-scale lamellae behavior during the foam-assisted CO2 displacement inside heterogeneous grain-based pore network. Dynamic gas storage efficiency and lamellae transport behavior of multiple injection modes are compared, including co-injection at constant flow rate, co-injection at constant pressure, and surfactant-alternating-gas process at fixed foam quality. Besides, the impacts from presence of remaining oleic phase and varying distribution of water saturation on formation of immobile foam bank and preferential flow of continuous CO2 are studied, followed by comparison with quasi-static modeling results based on pore filling event network (PFEN) algorithm.
When oleic phase is absent, the experimental results show that the mobility adjustment ability of foam during CO2 sequestration is less effective at higher water saturation because of limited frequency of lamellae redistribution, which prevents further development of immobile foam bank. As water saturation reduces with continuous gas injection, active lamellae redistribution starts to weaken the preferential CO2 flow paths, form sufficient blockage along highly permeable region, and eventually divert discontinuous CO2 flow into unvisited region saturated with water. Finally, compared with ordinary foam-free CO2 sequestration process, introduction of foam effectively improves CO2 storage rate by making CO2 flow discontinuous and less mobile, even at unfavorable liquid saturation for mass transfer of foaming surfactant. The presence of remaining oleic phase has remarkable impacts on lamellae configuration of different foam regimes. Defoaming effect of oleic phase on foam displacement is apparent, but the impact is limited at high water saturation stage at which immobile foam bank has not sufficiently developed. Adjusting injection strategy can further optimize foam performance during CO2 sequestration in the presence of residual oil at lower water saturation by balancing the competition between reestablishment of immobile foam bank and frequency of activating preferential flow of continuous CO2.
This work provides a pore-scale evaluation of representative stages during foam-assisted CO2 sequestration, which reveals in-situ lamellae behavior from the reduction of preferential CO2 flow to the formation of immobile foam bank. Experimental results have shown the detailed motion of lamellae redistribution, which eventually reveals the controlling roles of CO2 injection strategy, distribution of remaining water saturation, and presence of oleic phase during foam-assisted CO2 sequestration process.