Carbon dioxide (CO2) displacement and storage are the most viable technologies for achieving carbon neutralization and enhancing low-permeability reservoir recovery. The current research focused on the evaluation of CO2 storage capacity and mechanism under different geological conditions but ignored the problem of CO2 storage time being too long. When CO2 was injected into the stratum for geological burial, it mainly existed in the form of geological structure burial in the initial stage of injection (within several decades), and the safety was relatively low. In the middle stage of injection (within 100 years), it changed from geological structure burial to bound storage and gradually to dissolved storage, and the safety was relatively good at this time. In the later stage of injection (thousands of years), the storage forms were mainly dissolved storage and mineralized storage, and the safety was the highest. Therefore, through laboratory experiments, studying how to improve CO2 mineralization and storage speed and shorten the CO2 storage time using chemical agents is of great significance.
Based on the actual CO2 storage technology in reservoirs, a CO2 storage experimental device under formation temperature and pressure conditions was independently built, and multimedia-assisted CO2 storage experimental research was conducted. The precipitation of potassium carbonate through the utilization of the ethanol + KOH solution system enabled CO2 capture and carbonization. The reaction process in the solution system was affected by the ethanol concentration, resulting in different CO2 carbonization amounts with the change in the ethanol concentration. Simultaneously, the precipitation-generated potassium-based acid salt could undergo a reaction with water to facilitate ethanol regeneration. This paper utilized experimental methods to investigate the CO2 capture efficiency of the ethanol + KOH system, real-time monitoring of ethanol content in the solution, and identification of the optimal ethanol concentration for the formation temperature. The solution was supplemented with KOH, followed by the utilization of regenerated ethanol from the solution’s carbonization reaction for subsequent carbonization, enabling the determination of the maximum CO2 capture capacity of the ethanol + KOH system. The CO2 burial experiment was conducted using a high-temperature and high-pressure core displacement device after injecting the ethanol + KOH solution. The characteristics of CO2 mineralization under different permeability/porosity conditions were discussed.
The research results indicated that the 96% ethanol + 3-g KOH solution demonstrated effective CO2 capture, resulting in an average precipitation of 4.56 g per capture. Simultaneously, following the saturation of the core with the 96% ethanol + 3-g KOH solution, CO2 injection was conducted to induce sediment formation, resulting in a reduction in core permeability of approximately 16.01%. After CO2 mineralization and burial, the average porosity of the low-permeability core decreased by 7.07%, and the porosity change rate was positively correlated with porosity. The results of the CO2 storage experiment indicated that after the action of the 96% ethanol + 3-g KOH solution, CO2 could be effectively captured in the form of precipitates in the reservoir, with the largest degree of capture in medium to large pores. Compared with formation water, the composite solution studied in this paper can improve the CO2 storage efficiency by 30%. The 96% ethanol + 3-g KOH solution can accelerate the CO2 precipitation process in the reservoir and shorten the mineralization and storage time of CO2 in the reservoir.
This study proposed a new method to increase CO2 storage capacity by injecting a KOH + ethanol solution into a formation to improve CO2 mineralization and storage efficiency. Moreover, it realized the effective integration of the chemical industry and petroleum engineering disciplines and provided a new research approach for carbon peaking and carbon neutrality.
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