Cyclic CO₂ Injection Process Recovery Behavior in Classified Deep Formations

Area of Science:

• Petroleum Engineering
• Geoscience
• Reservoir Engineering

Background:

• Deeply buried formations present challenges in characterizing pore types.
• Understanding crude oil behavior under CO2 injection is crucial for enhanced oil recovery.
• CO2 huff-n-puff is a key technology for mobilizing oil in tight reservoirs.

Purpose of the Study:

• To classify deep formation pore types using integrated HPMI and NMR techniques.
• To investigate crude oil phase behavior and mobilization mechanisms under varying CO2 fractions.
• To quantitatively analyze oil mobilization during CO2 huff-n-puff in tight oil reservoirs.

Main Methods:

• Classification of pore types using high-pressure mercury injection (HPMI) and nuclear magnetic resonance (NMR).
• Phase behavior analysis and slim-tube experiments to study crude oil systems with different CO2 mole fractions.
• High-pressure gas injection experiments coupled with NMR to evaluate oil recovery from various pore types under different injection conditions.
• NMR T1/T2 analysis to differentiate adsorbed and free movable oil production.

Main Results:

• Successful classification of deeply buried formation pore types.
• Established a theoretical basis for analyzing crude oil mobilization mechanisms under CO2 injection.
• Quantified the oil recovery factor contribution from different pores during CO2 huff-n-puff.
• Distinguished between adsorbed and free movable oil production using NMR T1/T2.

Conclusions:

• The integrated HPMI and NMR approach effectively characterizes pore types and oil mobilization.
• CO2 huff-n-puff performance in tight oil reservoirs is quantitatively understood.
• Provides critical guidance for applying CO2 huff-n-puff and sequestration technologies in tight oil reservoirs.