Abstract:Tight reservoirs are typically developed through large-scale hydraulic fracturing to effectively connect natural fractures, which significantly influence CO? huff-n-puff oil recovery. To clarify the characteristics of oil mobilization under different fracture conditions in tight reservoirs, CO? huff-n-puff nuclear magnetic resonance (NMR) experiments were conducted for varying fracture apertures, along with micro-visualization experiments under multi-scale fracture conditions. The effects of fracture aperture and fracture density on CO? huff-n-puff performance were systematically investigated. The results show that in the case of a single fracture, increasing the fracture aperture enhances the mobilization of crude oil in both the fracture and surrounding matrix. When the fracture aperture increased from 20μm to 70μm, recovery improved by 9.20%. Under multi-scale fracture conditions, increasing fracture density enhances reservoir connectivity and expand the swept volume of CO2. Compared to simple fracture model, complex fracture model improved matrix oil mobilization by 4.26%. The enhancement in recovery factor primarily occurs during the first two huff-n-puff cycles, with the incremental oil recovery effect diminishing in subsequent cycles. Increasing fracture aperture and fracture density effectively improve matrix oil mobilization in tight oil reservoirs. The research can provide valuable guidance for improving CO2 huff-n-puff recovery rates in tight oil reservoirs.