Experimental study on enhanced oil recovery in deepwater carbonate reservoirs via reinjection of high-CO2 produced gas
In one deepwater carbonate M reservoir,the gas-oil ratio is as high as 200～350 m3/m3,and the produced gas contains over 40%CO2.To reduce carbon emissions and fully utilize the high-CO2 produced gas to enhance oil recovery efficiency,this study conducted continuous gas injection,water flooding,and water alternating gas(WAG)injection,experiments under simulated reservoir conditions.It further analyzed the oil displacement efficiencies of different displacement methods and the impacts of core heterogeneity,gas injection rate,and injection pressure changes on the effectiveness of WAG injection.The results indicate that WAG injection achieves the highest oil displacement efficiency,up to 71.88%,followed by continuous gas injection at 56.83%.These are respectively 29.8 and 14.75 percentage points higher than water flooding,which has an oil displacement efficiency of 42.08%.Core heterogeneity,gas injection rate,and injection pressure significantly influence the oil displacement effectiveness of WAG injection.Greater core heterogeneity leads to poorer water control and delayed gas breakthrough,resulting in lower displacement efficiencies.Injection gas at a rate higher than the optimal level can cause premature gas breakthrough,ultimately reducing recovery.Additionally,maintaining injection pressure within the miscible displacement conditions is beneficial for improving oil displacement efficiency.This study provides a basis for utilizing high-CO2 produced gas in deepwater carbonate reservoirs through WAG injection to enhance oil recovery.
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