Abstract
CO2 geological sequestration is the most realistic and feasible technology to ensure large-scale carbon emission reduction to achieve the global carbon capping and carbon neutrality goals, and the leakage risk assessment of the sequestration system is the basis of safe sequestration. However, at present, leakage risk assessment mainly focuses on the simulation and research of ultra-long-term (more than 1000 years) storage process, and few scholars has studied the impact of development operations, such as CO2 huff-n-puff, on caprock leakage risk. In this paper, a numerical model of CO2 huff-n-puff that incorporates gas adsorption/desorption, diffusion, and hydrochemical reaction is established, and the leakage risk of caprock during CO2 huff-n-puff in tight reservoir is evaluated. The model's reliability is verified by matching with the production history and CO2 mole fraction of commercial software. Finally, the effects of parameters, including adsorption/desorption, diffusion, hydrochemical reaction, caprock permeability, caprock-to-reservoir thickness ratio, and CO2 injection rate on leakage risk of caprock during CO2 huff-n-puff, are analyzed. The results show that after 15 consecutive cycles of huff-n-puff operations, the escape ratio of CO2 in the caprock is less than 2%, and the injection rate of each cycle is 1 × 105 m3/d for 120 days. It is proved that huff-n-puff operation improves the recovery of tight gas reservoirs and has little effect on the sealing efficiency of caprock sealed for a long time in the later stage. This work provides a theoretical basis for the leakage risk assessment of CO2 geological sequestration after development operations.
Published Version
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