CO2-Assisted Mitigation of Coupled Water Blocking and Retrograde Condensation Damage in Condensate Gas Reservoirs

Abstract

: This study elucidates the coupled damage mechanisms induced by retrograde condensation and water blocking in low-permeability edge-bottom water condensate gas reservoirs and develops an optimized CO 2 injection strategy for simultaneously enhancing hydrocarbon recovery and geological carbon storage. Using the K condensate gas reservoir in the Junggar Basin as a case study, nuclear magnetic resonance (NMR) measurements and long-core displacement experiments are integrated to characterize the evolution of water-lock and retrograde-condensation damage across pore and core scales and to unravel the mechanisms governing its mitigation by CO 2 injection. The results reveal a pronounced synergistic interaction between the two damage mechanisms, with their combined impact on gas-phase permeability substantially exceeding that of either mechanism acting independently. CO 2 injection effectively alleviates the coupled damage through the combined effects of miscible displacement, interfacial-tension reduction, and condensate vaporization. Building on these experimental insights, a high-fidelity three-dimensional compositional reservoir model is established to optimize an integrated CO 2 injection-production strategy. The resulting scheme comprises two cycles of CO 2 huff and puff, with an injection volume of 4000 t per cycle, followed by continuous CO 2 displacement at 240 t/d and an injection pressure of at least 24 MPa. Numerical predictions indicate that this strategy can sustain stable production for 15 years, achieving cumulative recoveries of 6.2 × 10 8 m 3 of natural gas and 3.5 × 10 4 m 3 of condensate oil, while simultaneously sequestering 1.125 × 10 6 t of CO 2 . These findings demonstrate that CO 2 injection can effectively overcome the coupled flow impairment associated with water blocking and retrograde condensation while providing a pathway toward the integrated recovery of condensate gas and geological CO 2 storage.