延长油田低渗透油藏CO2驱油适应性分析OA

CO2 flooding adaptability evaluation was carried out for Chang 6 low permeability reservoir in block X of Yanchang oilfield.The aver-age porosity of Chang 6 reservoir in the study area is 9.6%,and the average permeability is 0.94×10-3 μm2.The correlation between porosity and permeability is good,and the fractures are not developed.Chang 4+5 above Chang 6 reservoir develops 70-90 m thick mudstone ca-prock,which has the potential of large-scale CO2 displacement.Through high temperature and high pressure PVT experiment and core displace-ment experiment,the key parameters of the interaction between CO2 and reservoir fluid were determined.The results show that the C7+content of reservoir fluid is 84.626 mol%,and the gas oil ratio is 8.75 m3/m3,which belongs to the typical low gas oil ratio,low viscosity,under satu-rated black oil.CO2 injection can significantly reduce the viscosity of crude oil(by91.4%)and make the volume expansion of crude oil(ex-pansion coefficient 1.48);According to the long thin tube core displacement test,the minimum miscible pressure of the reservoir is determined to be 14.28 mpa;The CO2 solubility increases with the increase of equilibrium pressure and decreases with the increase of temperature;The oil displacement efficiency is analyzed from the injection pressure and different injection methods.The final recovery factor increases with the in-crease of CO2 displacement pressure.The recovery factor under miscible conditions is much higher than that under immiscible conditions.Com-pared with continuous gas injection,the recovery factor increase of WAG is significantly higher,up to21.54%.It is clear that Chang6 reser-voir in block X has good CO2 displacement adaptability.