Cyclic CO ₂ Injection Process Recovery Behavior in Classified Deep Formations

The deeply buried formation pore types were classified by using high-pressure mercury injection (HPMI) and nuclear magnetic resonance (NMR) techniques. Phase behavior analysis and slim-tube experiments were conducted to investigate the properties of crude oil systems under different CO₂ injection mole fractions, providing a theoretical basis for subsequent analysis of crude oil mobilization mechanisms. High-pressure gas injection experiments combined with NMR technology were employed to evaluate the contribution of the oil recovery factor from varying pores under different injection conditions, enabling a quantitative analysis of the microscopic distribution characteristics and influencing factors of oil mobilization during the CO₂ huff-n-puff process. Consequently, NMR <i>T</i> ₁/<i>T</i> ₂ was used to distinguish the adsorbed and free movable oil production differences during the CO₂ huff-n-puff. Notably, this comprehensive approach provides critical guidance for the application of CO₂ huff-n-puff and sequestration technologies in tight oil reservoirs.