The Damage Caused by Particle Migration to Low-Permeability Reservoirs and Its Effect on the Seepage Capacity after CO 2 Flooding.

CO₂ flooding technology is an effective technical means for tertiary oil recovery in high water cut reservoirs. Using an existing well pattern to inject CO₂ is an economical and feasible development method under low contemporary oil prices. Although the particle migration caused during the displacement process will block the pore throat of the rock, the injection of CO₂ can effectively reduce the CO₂ injection pressure, and the dissolution that occurs during the injection process improves the seepage capacity of the fluid as a whole. In this study, assessments of particle migration and plugging after CO₂ flooding and evaluations of rock dissolution by CO₂-aqueous solution were carried out, and the variation characteristics of the relative permeability curve before and after displacement were evaluated, further explaining the influence of CO₂ flooding on reservoir seepage capacity. The results show that, in the process of CO₂ injection, the injection pressure decreases under different injection rates. After CO₂ flooding under oil conditions, the core permeability loss was 43.8%, and after cleaning with toluene and anhydrous ethanol, the core permeability recovery was 24.3%, indicating that the particles were bound by crude oil during the migration process and accumulated into clusters, resulting in blockages. Although there was a certain degree of blockage, the CO₂-aqueous solution mainly reacted with chlorite and released Ca²⁺, Mg²⁺, and Fe²⁺ ions. The concentration of Ca²⁺ increased by 157.43%, the concentration of Mg²⁺ decreased by 43.33%, and the concentration of Fe²⁺ decreased by 50.47%, indicating that, although the generated MgCO₃ and Fe₂O₃ blocked the pore throat of the rock, the overall dissolution effect of CO₂ on CaCO₃ was stronger, and the overall seepage capacity of the fluid was improved. To a certain extent, this technique can improve the water injection capacity and the effect of subsequent water flooding. [ABSTRACT FROM AUTHOR]