Experimental Investigation of CO2 Huff-and-Puff Enhanced Oil Recovery in Fractured Low-Permeability Reservoirs: Core-Scale to Pore-Scale

Abstract

To understand the impact of CO2 huff-and-puff on oil mobilization in tight reservoirs with varying fracture scales, we performed nuclear magnetic resonance (NMR) and microscopic visualization experiments, focusing on different fracture sizes and multi-scale fracture conditions. Our study investigates how different fracture sizes and densities influence the efficiency of CO2 huff-and-puff techniques in these environments. The results show that in scenarios with a single fracture, larger fracture apertures significantly boost oil mobilization within the fracture and the surrounding matrix. For instance, increasing the aperture from 20 μm to 70 μm improved the recovery factor by 9.20%. In environments with multiple fractures, greater fracture density enhances reservoir connectivity, and increases the CO2 sweep area, and the complex fracture model shows a 4.26% increase in matrix utilization compared to the simple fracture model. Notably, the improvement in recovery due to multi-scale fractures is most significant during the first two huff-and-puff cycles, with diminishing returns in subsequent cycles. Overall, increasing both fracture size and density effectively enhances crude oil mobilization in tight reservoirs. These findings provide valuable insights into improving the recovery efficiency of CO2 huff-and-puff techniques in tight oil reservoirs.