Study On Mechanism Of CO 2 Enhanced Oil Recovery By Volatile Oil In Hua 3 Fault Block

After years of depletion development,Hua3-fault block volatilization oil reservoir currently exists the problems of high reservoir pressure decline,low pressure level,fast productivity decrease,and high natural and comprehensive decline etc.Since the volatilization oil reservoir is under low development degree and possesses high remaining reserves,it is more important to promote further research on oil recovery improvement mechanism of gas injection of Hua3-fault block oil filed development,especially oil recovery improvement of C02 injection.Through researching the fluid phase of Hua3-fault block volatilization oil reservoir stratum,research on oil recovery mechanism of gas injection and feasibility research on numerical simulation of oil reservoir gas injection are conducted to explore the reasonable development way of Hua3-fault block volatilization oil reservoir.Following knowledge is gained through relative research:Hua3-fault block volatilization oil reservoir is the kind of light reservoir of relatively high gas in high-temperature and normal-pressure.Currently,the oil reservoir is under depletion development and has high pressure decline,largely increased gas-oil ratio and decreased productivity.So maintaining the formation pressure above the bubble pressure helps to increase the recovery.It can be seen from Hua3-fault block volatilization oil reservoir C02 and N2 injection MMP research.The differential pressure of stratum pressure and dew point pressure is relatively larger.In depletion development,when the stratum pressure is lesser than bubble point pressure,the crude oil will volatilize.And the fluid liquid measure line is relatively dense.When the pressure decrease is small,the fluid liquid decrease is obvious.The Hua3-fault block volatilization oil reservoir can reach the miscible-phase displacement effect under 21.OOMPa when injecting CO2,while the pressure shall be 31.75 to reach miscible-phase displacement when injecting N2.Only by reaching CO2 to reach miscible-phase displacement under stratum pressure.The main mechanisms of gas injection to improve oil recovery are mutually soluble extraction,extraction,dilatation and extension,viscosity and concentration reduction.It can be seen from core displacement experiment that the Hua3-fault block volatilization oil reservoir can reach miscible-phase under 22MPa when injecting CO2 and has better development effect.The difference of oil recoveries when injecting CO2 under higher pressures is small.Injecting N2 displacement under 35.2MPa pressure has 20.887%lesser oil recovery than CO2.Thus,the CO2 injection can greatly enhance oil recovery.Injecting parameters selection is conducted based on reserve matching and historical matching,and demonstration to the influence of development way,gas injection well network,single-well's mean gas injection speed,total CO2 injection volume,and pressure maintaining level of CO2 displacement stratum aspects on development effect is conducted.The best development method is selected and the accumulative oil production of recommended plan is 392896x104m3.Through this mathematical model research,it can be found that the un-extraction degree of this plan in prediction stage is 35.23%,15.56%than depletion development(19.67%).The oil saturation is the minimum after the ending of gas displacement plan simulation.The gas displacement plan is significantly better than water displacement plan that gas injection can maintain a stable stratum pressure and decrease the large number of degassing in volatilization oil reservoir.As a result,the Hua3-fault block volatilization oil reservoir can be injected with CO2 to realize miscible-phase displacement and improve oil recovery based on stratum condition and practical situation.