Study On Recovery Mechanism Of L4 Fault Block Condensate Gas Reservoir Enhanced By Injecting Natural-Gas Rich In CO₂

The current formation pressure of L4 fault block is attenuated seriously,a large amount of condensate in the formation has not been produced,it is necessary to carry out measures to improve the recovery of condensate.The L21 fault block adjacent to the L4 fault block,is a natural gas reservoir rich in CO2.By reinjection L21 gas to the L4 fault 'olock can improve the remaining oil recovery.It also achieved the comprehensive utilization of L21 fault block formation fluid.This paper aims to clarify recovery mechanism of L4 fault block condensate gas reservoir enhanced by injecting natural-gas rich in CO2.The study includes the fluid phase characteristics of the L4 fault block condensate gas reservoir and the gas phase characteristics of different parts of the oil and gas reservoir;The minimum miscibility pressure test of the remaining oil in the formation and the residual oil seepage characteristics;the numerical simulation was carried out to evaluate the application effect of L4 fault block injection of CO2 natural gas to improve condensate recovery for 2 injection and 3 mining schemes.Through above research,the following results and understanding have been achieved:(1)Based on fault block near-critical saturated condensate gas reservoir,phase analysis?mix characteristics?oil displacement efficiency?practical application to improve condensate recovery method;(2)The phase characteristics of fluids in CO2-rich natural gas reservoirs show that the dew point is lower than general condensate gas reservoirs,and the dark brown haze phase characteristic of critical opalescence occurs.At present,gas injection in the formation condensate gas system can reduce the saturation pressure thus reduce the formation anti-condensation damage.At present,the formation condensate system is rich in CO2 natural gas,which can achieve a good capacity expansion expansion effect,which is conducive to enhance oil recovery by miscible flooding;(3)The displacement experiment shows that when the injection pressure is greater than the minimum miscible pressxure,the injection of CO2 rich natural gas can greatly increase the recovery of residual oil in the formation;it is also found that the extended displacement multiple can occur at the injection end in the near miscible pressure interval.Condensate gas flooding mixed phase to improve oil displacement efficiency;compare with the vapor gas flooding phase pressure zone,the recovery of the near-miscible pressure zone displacement can be increased after prolonging the flooding multiple;(4)The simulation application shows that the natural gas rich in CO2 has a wide spread area and strong dissolving ability in the formation,which can effectively achieve the mixed phase,and the double mechanism of evaporation-extraction under the action,effectively increase the degree of formation condensate recovery.