Abstract:

The pore utilization characteristics of CO₂ during shale oil displacement are a crucial indicator for evaluating its effectiveness in enhancing shale oil reservoir recovery rates. Therefore, experiments on supercritical CO₂ displacing shale cores were conducted in the laboratory, and nuclear magnetic resonance（NMR） online core scanning technology was used to study the pore utilization characteristics and patterns of CO₂ displacement in shale oil reservoirs. The results indicate that immiscible flooding by supercritical CO₂ mainly develops the oil in shale pores with radius of 0.1~3.0 μm, but the oil content in pore radius less than 0.008 μm actually increases. The analysis shows that CO₂ brings shale oil from large pores into small pores through pressure difference and diffusion effect in the shale layer and makes oil undergo adsorption and retention. After a displacement time of five hours, the recovery rate of shale oil by CO₂ displacement reached 35.7%, indicating a relatively effective oil displacement result.

Key words: supercritical CO₂, shale oil, nuclear magnetic resonance, pore development characteristic, oil recovery