Experimental Study on Improving Condensate Oil Recovery by CO₂ Huff and Puff in Condensate Gas Reservoirs

the application of CO₂ injection to improve the recovery of natural gas and condensate is still in the development stage. The injection mode, injection time and the interaction mechanism between CO₂ and reservoir fluid are not clear. Through the improved constant volume depletion experiment of CO₂ injection with condensate gas and the measurement experiment of oil-gas interfacial tension, a stepped incremental CO₂ injection huff and puff method is proposed on the basis of determining the maximum reverse condensate pressure, liquid volume and CO₂ condensate oil interaction mode, and the huff and puff effect and CO₂ storage ratio are evaluated by full diameter core experiment. The results show that after the condensate gas is injected into CO₂, the dew point pressure, the maximum reverse condensate pressure and the condensate volume are continuously reduced, the critical point moves to the lower left corner, the two-phase envelope area shrinks inward, and the envelope area becomes smaller. The phase mixing between CO₂ and condensate can be achieved gradually only after multiple contacts. The higher the CO₂ pressure is, the fewer contacts are required to achieve the phase mixing. The condensate recovery of four rounds of incremental CO₂ huff and puff is 1.2%, 14.4%, 25.8% and 3.6% respectively, which is 45% higher than that of natural depletion condensate. The proportion of CO₂ storage decreases with the increase of throughput times, which are 82.2%, 72.1%, 46.4% and 9.2% respectively. The optimal number of CO₂ throughput times should not exceed 3. The effect of stepped incremental CO₂ huff and puff is mainly affected by CO₂ injection pressure and core system pressure. When the CO₂ injection pressure is lower than MMP, it is not conducive to CO₂ huff and puff and storage. The research results provide a reference for the efficient development of condensate gas reservoirs and the improvement of retrograde condensate damage.