Study On Mechanism Of Enhanced Oil Recovery By Gas Injection In The Middle And Late Phases Of Condensate Gas Reservoir With High Condensate Oil Content Development

During the middle and late stages of condensate gas reservoir development,the phenomenon of intensified retrograde condensate pollution,drastically reduced effective gas permeability,low efficiency of injected gas,and low condensate oil recovery efficiency have seriously affected the efficient development of condensate gas reservoirs.Especially for those condensate gas reservoirs with high condensate content in the middle and late stages of development,these problems are even more prominent.Therefore,it is of great significance to clarify the mechanism of enhanced recovery by gas injection in late stage of development of condensate gas reservoirs with high condensate oil content and to efficiently develop condensate gas reservoirs in later stages.In view of the above,this article mainly uses the combination of indoor experiments and numerical simulation to carry out experiments and simulations of reservoir retrograde condensate damage,gas-injected phase state,and improving the recovery of condensate oil by injection of CO2 in the middle and later stages of the development of high condensate oil condensate gas reservoirs.The change of gas effective penneability for condensate gas samples with different condensate content in different seepage areas,the miscibility between CO2 gas and remaining condensate oil and the mechanism of improving condensate oil recovery by CO2 injection are mainly analyzed.Quantitatively evaluate the degree of reservoir retrograde condensate pollution in the late stage of development of condensate gas reservoirs with high condensate content,the miscible mechanism of CO2-residual condensate oil.The effect of different CO2 injection schemes on condensate recovery was effectively compared.According to the study of the above problems,the main understanding is as follows:(1)The retrograde condensation pollution evaluation experiment with high condensate oil content shows that the greater the variation of pressure drop and displacement multiplier,the greater the change of effective permeability of gas phase.The effective permeability of gas phase in the far well area(individual depletion)and the near well area(combined depletion)are more consistent,and the near-wellbore area's permeability decline is greater than in the far well area.For the same seepage area,whether it is the near well area or the far well area,the higher the condensate content,the greater the decrease in the effective permeability of the gas phase,and the more serious the retrograde condensate pollution.(2)The CO2 phase state experiment of the remaining condensate system in the formation shows that:with the increase of the injected CO2 content,the saturated pressure and the dissolved gas-oil ratio of the remaining condensate oil system continuously increase.The more the injected CO2 content,the greater the increase in the dissolved gasoline ratio,but the overall increase in the saturation pressure is not significant.(3)The CO2 phase state simulation of the remaining condensate system in the stratum shows that:with the increase of c injection volume,the remaining condensate system becomes lighter,the anti-evaporation effect of condensate increases,the saturation pressure of the system rises,the critical point of the P-T phase diagram gradually shifts to the upper left,and the critical pressure rises first and then decreases,and the critical temperature gradually decreases.When the injection of CO2 reaches 80%-90%,the phase inversion occurs,and the remaining condensate system gradually becomes a condensate gas system.(4)The CO2 fine tube experiment of residual condensate system in formation shows that:with the increase of CO2 injection and injection pressure,the degree of condensate recovery gradually increased;the higher the pressure,the higher the degree of condensate recovery and the later CO2 breakthrough.Before the breakthrough of C02,the gas-oil ratio of the system changed little,and the degree of condensate production changed greatly;after the CO2 breakthrough,the gas-oil ratio of the system rose sharply,and the recovery of condensate oil increased slowly.(5)The CO2 slimline simulation of the remaining condensate system in the formation shows:under the conditions of formation temperature(92.8?)and pressure(11MPa),the remaining condensate system is not miscible with the CO2 injection gas.In the process of multiple contact between C02 with the remaining condensate,although the heavy components in the condensate are reduced,the change is not obvious.With the injection of C02 gas,the gas phase saturation in the slim tube gradually decreases,and the oil phase saturation gradually increases.Before CO2 breakthrough,the more C02 injection,the wider the gas spread,and the longer the oil and gas transition zone;the higher the injection pressure,the shorter the oil and gas transition zone,and the closer the C02 flooding to the piston displacement,the greater the flooding efficiency.(6)For condensate gas reservoirs with high condensate content,numerical simulations of C02-enhanced condensate recovery showed that:The CO2 flooding effect of scheme 2 well network injection is better than scheme 1;the higher the CO2 injection rate,the higher the oil displacement efficiency;the higher the injection pressure,the higher the growth rate of the condensate recovery;the final condensate recovery by the bottom injection method is higher than that in the middle and top injection.