Research of Chemical Additive-Assisted CO2 Huff-n-Puff for Enhanced Heavy Oil Recovery

Carbon Capture, Utilization and Storage (CCUS) is a critical decarbonization technology, and CO2-enhanced oil recovery (CO2-EOR) effectively combines CO2 geological storage with crude oil production, especially for high-difficulty heavy oil reservoirs. To overcome viscous fingering and early gas channeling in conventional CO2 huff-n-puff, this study focused on chemical additive-assisted CO2 huff-n-puff for cold heavy oil production in the Gudong reservoir. Through screening and optimization, 0.5% HY-2 foaming agent and 0.5% SR-1 viscosity reducer were identified as optimal, showing stable performance and strong synergy with CO2. High-temperature high-pressure experiments indicated the suitable CO2 injection volume is 0.15–0.2 PV, the optimal injection sequence is chemical solution followed by CO2, and the technology is applicable for crude oil viscosity below 3000 mPa·s. The 0.5% HY-2 + 0.5% SR-1 system enhanced oil recovery to 45.07%, 14.4% higher than pure CO2 huff-n-puff, while the 0.5% SR-1 single-agent scheme achieved 42.13% recovery with better economics. The main mechanisms include emulsification and viscosity reduction, gas mobility control, and expanded sweep efficiency, supplemented by CO2 dissolution, oil swelling, and elastic drive. Field tests in four wells showed an average daily oil increase of 2.7 t per well and a total incremental oil of 1748.6 t, with a CO2 storage rate of 80.4% and an input-output ratio of 8.02:1. This study verifies the technical and economic feasibility of chemical-assisted CO2 huff-n-puff, providing support for its field application and a practical route for heavy oil EOR and carbon reduction coordination.