Study On Phase Behavior Characteristics Of Impure CO₂ Near Miscible Flooding In QHD 29-2 Reservoir

CO₂ flooding has become a win-win strategy to improve oil recovery and achieve greenhouse gas storage at home and abroad.It is of great significance for the study of near miscible pressure interval and the characteristics of the fluid phase state of CO₂near miscible flooding.Taking the QHD 29-2E reservoir as an example,this topic will carry out the study of the minimum miscibility pressure and phase state characteristics and the control technology of the offshore oil reservoir with high CO₂ production gas re-injection.By means of multiple group of slim-tube test?encryption test points?,combined with numerical simulation?ECLIPSE component model?and other technical means,respectively from the recovery ratio of engineering field and interfacial tension angle of physical chemistry field,the near miscibility is defined clearly.The comprehensive determination method of the lower limit of near miscible pressure interval is established.On this basis,control measures of CO₂ near miscible flooding can not be realized from the angle of adjusting injected gas composition,so as to provide the technical reserve for the high efficiency development of offshore oil reservoir for the impure CO₂ near miscible flooding.The results of the study are as follows:?1?The method of determining near miscible pressure interval based on IFT and oil displacement efficiency is used to calculate the CO₂ purity of 100%,85%,80%,70%,55%,40%and 24%of near miscible pressure interval for the 1 segments of the target reservoir.The near miscible pressure interval of 100%CO₂ is[26.52-32.9]MPa.?2?Under the formation condition?31.96MPa?,the CO₂ purity interval of the near miscible flooding in the target reservoir is 64-100%,so the near miscible displacement can be realized when the purity of injected gas CO₂ is higher than 64%.?3?The purity of CO₂ in injected gas is reduced by 10%,to ensure that gas flooding in the well section is a near miscible drive,and about 2.5%of the intermediate component?C₂-C₆?should be added to balance the influence of the impurity gas mixing on the near miscible pressure range.