CO2 utilization and sequestration in Reservoir: Effects and mechanisms of CO2 electrochemical reduction

Owing to the harmful consequences of the greenhouse effect, mankind has reached a consensus to reduce CO 2 emissions. CO 2 utilization and sequestration is considered the most feasible solution for realizing an effective and economical sequestration of CO 2 . Herein, CO 2 -enhanced oil recovery (EOR) is a representative strategy owing to its tremendous sequestration capacity and reasonable economic viability. However, the low sequestration stability and the accompanying secondary disasters have hindered its wider application. Considering this, a novel CO 2 utilization and sequestration technology, i.e., CO 2 electrochemical reduction (CO 2 RR)-EOR technology was proposed and its effects and mechanisms were studied. First, a SnO 2 catalyst that can be used in the coreflooding experiments was synthesized and its efficiency on CO 2 RR was evaluated. Then, coreflooding experiments using the SnO 2 catalyst were conducted to study the influence of CO 2 RR on the CO 2 sequestration and oil recovery. Next, contact angle and interfacial tension were measured to analyze the effect of the CO 2 RR on the CO 2 -crude oil-brine-rock interaction. Finally, the CO 2 RR-EOR mechanism was proposed. Multiple experiments revealed that the low-cost and easy-synthesis SnO 2 catalyst, which was characterized by the 3-dimensioned hierarchical and porous structure, was in the high efficiency and strong stability. Coreflooding results illustrated that the CO 2 RR remarkably enhanced CO 2 sequestration and oil recovery. At the optimal cell potential of 3.75 V, the CO 2 sequestration efficiency and oil recovery were as high as 75.93% and 43.8%, respectively, which are much higher than those (50.56% and 37.9%, respectively) achieved in conventional CO 2 flooding. Contact angle and interfacial tension results indicated that the CO 2 RR has a significant impact on the CO 2 -crude oil-brine-rock interaction. At the optimal cell potential, the crude oil-contact angle and the interfacial tension were 36.2° and 8.9 mN/m, respectively, which are much lower than those (64.6° and 16.4 mN/m, respectively) achieved in conventional CO 2 flooding; the CO 2 -contact angle was 52.2°, which too is much larger than that (31.7°) achieved in conventional CO 2 flooding. In this technology, the CO 2 RR converts the injected CO 2 into formate to sequestrate itself, and meanwhile alters the CO 2 -crude oil-brine-rock interactions, resulting in enhanced CO 2 wettability and consequently increases CO 2 trapping and retention; causing the weakened oil wettability and the enhanced oil-brine interaction, and finally enhances oil recovery. CO 2 RR-EOR can be a novel, efficient, and economically-viable CO 2 utilization and sequestration technology, which provide a feasible option for the future industrial CO 2 emission reduction.