Study On Influential Factors Of Displacement Efficiency Of CO₂ Flooding

As an EOR tenique. CO₂ flooding has been widely used all over the world due to its advantages of wide application scope, high displacement efficiency. low cost. etc. On the basis of the present situation and development prospect of CO₂ flooding, the minimum miscibility pressures (MMP) between CO₂ and oil in two oil samples are tested using slim-tube. The composition of oil , the purity of CO₂ and the effect of reservoir temperature on MMP are analyzed, and the methods to reduce MMP are discussed in this thesis.Through the experiments of CO₂ flooding , the parameters of recovery are tested under various pressures, gas to oil exchange ratio, produced gas oil ratio, gas injection capability, etc. The following results are obtained: as injection pressure rises, the time of gas breakthrough, the recovery at the time of gas breakthrough, the ultimate recovery, the gas to oil exchange ratio, the CO₂ injection capability are all improved, and the dissolved gas oil ratio has increased, which are caused by the changes of high-pressure physical properties of oil. the oil volume expansion, the reduction of viscosity and interfacial tension, etc. as the injection pressure increases. When certain pressure value is reached, both of the recovery increasing degree and the gas to oil exchange ratio draw down with the increase of pressure. The ultimate recovery through CO₂ flooding is higher than that through water flooding. In addition, the capability of CO₂ injection is stronger than that of water injection. The lower the rock permeability, the higher the CO₂ to oil exchange ratio. After gas breakthrough, the produced gas oil ratio is higher in the low permeability rock sample than the rock sample of high permeability. And the CO₂ injection capability of the low rock sample is lower than that of the high permeability rock sample.During the process of CO₂ injection, the precipitation amount of asphaltene is determined by the synthetic influences of precipitation and dissolution. As pressure rises, the precipitation amount shows the trend that it firstly increases and then decreases. With the asphaltene precipitation, the rock permeability reduces correspondingly.