The Mechanism Of Improving The Recovery Of CO 2 In The Late Stage Of The Development Of The Bailian Condensate Gas Reservoir

The condensate gas reservoir of BaiLian has been in the later development of depletion, in the stage of the natural energy is nearly exhausted and production will be stopped or intermittent, so it needs to supplement the formation energy to enhance oil recovery. This research scientific significance lies in exploring the mechanism that condensate gas reservoir in later development of injecting CO2/N2to improve the condensate oil recovery. This research focuses on the dynamic characteristics of condensate gas reservoir which was put into production since the development; the special phase behavior of gas condensate reservoir original fluid in the early development; the special phase behavior of injecting CO2/N2into the remaining condensate oil and gas system/condensate oil system under present reservoir conditions; the MMP of residual oil system by CO2/N2injection at present temperature and pressure; Then, the three dimensional numerical simulation models were used to evaluate the mechanism of CO2/N2injection for enhancing the recovery of condensate oil. Through the research, the following conclusions are obtained.(1) According to the dynamic production data of the block4of the BaiLian condensate gas reservoir, it has entered the depletion period. The exploitation of condensate oil is difficult. Some wells have accumulated fluid and need to supply the formation energy.(2)Constant volume depletion (CVD) experiment and simulation show that when the system pressure drops to the dew point pressure (26.58MPa) below, the formation began to precipitate condense oil, after the system of Constant volume depletion,the P-T ternary phase diagrams is broadened and shifted to the right than before. The critical point is to the right deviation. It is showed that the formation fluid properties convert from condensate reservoir to volatile oil reservoir.(3)The condensate system of residual gas and CO2/N2expansion experiment and simulations show that the expansion factor of residual oil and gas condensate system are higher than the CO2infusion. It shows that CO2is compatible with the formation fluid system better.(4)Residual condensate gas reservoir/residual condensate system CO2/N2phase dynamic characteristics simulation study shows that CO2/N2injection can make the formation fluid to the light direction. But the N2effect is quite poor and not easy to invert for condensate gas system, so the choice of gas injection miscible flooding EOR should give priority to CO2.(5)CO2/N2residual condensate system minimum miscible pressure tubes of experimental test and numerical simulation shows that the minimum miscibility pressure of CO2-residual condensate system less than that of N2,and the minimum miscibility pressure is less than the original formation pressure. Therefore, CO2and residual condensate in the formation could make the miscible flooding.(6)Three dimensional numerical simulation study of CO2flooding injection shows:only considering single factor conditions, injection pressure, injection quantity or injection rate increases, the recovery degree of condensate oil will be higher. However, taking the rate of oil and gas channeling and other factors into account, the final optimization of gas injection rate, reasonable injection volume and pressure are90000m3/day,0.8HCPV and26MPa.