Quantifying the Pore Throat Mobilization Characteristics in Volatile Reservoirs via In Situ NMR Technology: Implications for CO2-Enhanced Oil Recovery

Integrating enhanced oil recovery (EOR) with geological carbon storage presents a dual-strategy solution for sustainable hydrocarbon production and greenhouse gas emission mitigation. CO2 flooding, particularly under miscible conditions, is a pivotal technology in this endeavor. This study employs advanced in situ nuclear magnetic resonance (NMR) imaging to visually and quantitatively investigate the pore-scale mechanisms of CO2 flooding in fractured carbonate rocks from a Kazakhstan oilfield. By establishing a novel correlation between NMR data and pore throat size distribution, we quantify the lower limit of pore throat mobilization—a key parameter for evaluating storage and displacement efficiency. Results show that miscible CO2 flooding significantly reduces this limit to the submicron scale (0.1 μm) in matrix rocks, dramatically improving oil recovery from small pores. However, fracture networks dominate fluid flow, leading to early gas breakthrough and severely limiting CO2 penetration and miscible displacement in the matrix. The study provides pore-scale insights for optimizing CO2 injection strategies to maximize both hydrocarbon recovery and CO2 storage potential in complex carbonate formations. The study elucidates the microscopic mobilization mechanisms and remaining oil distribution patterns during CO2 flooding in volatile reservoirs. Moreover, it represents an environmentally friendly methodology for mitigating greenhouse gas emissions.