Characteristics of Asphaltene Deposition and Formation Damage Mechanisms in Heavy Oil Under Different CO2 Dissolution Concentrations

Asphaltene deposition is a key issue constraining the field application of CO2 flooding, yet the deposition characteristics and formation damage mechanisms under different CO2 dissolution concentrations remain unclear. In this study, the asphaltene deposition behavior of heavy oil under different CO2 dissolution concentrations was systematically investigated under realistic reservoir conditions. Static deposition experiments and core flood tests were performed to quantitatively characterize the deposition amount, particle size distribution, and the extent of permeability impairment. The results show that the asphaltene deposition amount increases monotonically with CO2 dissolution concentration, reaching 2.12 wt.% at 50 m3/m3. The particle size increases significantly with increasing CO2 dissolution concentration, with the mean diameter increasing from 0.70 μm to 6.72 μm at 50 m3/m3. Based on a pore-scale evaluation model correlating deposition thickness with permeability impairment, the deposition effect was quantitatively assessed. According to the model, permeability loss reaches 59% when the deposition thickness attains 20% of the pore radius. Low-permeability cores exhibit significantly higher sensitivity to asphaltene deposition, with permeability reduction reaching 52.3% at 50 m3/m3 CO2, compared to only 20.8% in high-permeability cores. This disparity is attributed to the smaller pore throat radii, higher specific surface area, and more complex pore structures of low-permeability formations. This study provides a quantitative theoretical framework for predicting asphaltene-induced formation damage and optimizing CO2 injection strategies in heavy oil reservoirs.