A calculation method for waterflood recovery factor of oilfields developed by early polymer flooding

Displacement characteristic curve method is an important method to calibrate the recovery factor of oilfields, and it can be used in early polymer flooding oilfields to calculate their recovery factor of polymer flooding. At present, there is no evaluation criterion for the development effects of early polymer flooding oilfields. To deal with this situation, the main factors influencing the characteristic parameters of the linear section of displacement characteristic curve were analyzed, and the relative permeability curves measured in water flooding and polymer flooding experiments and the Type A displacement characteristic curve were combined. And accordingly, the slope-intercept numerical relationships of linear section of displacement characteristic curve under polymer flooding and water flooding conditions were derived, and the formula for calculating the waterflood recovery factor of early polymer flooding oilfields was established. It is shown from the case calculation results that waterflood recovery factor can reach 29.14%, which is 15.07% lower than that of early polymer flooding. The main factors influencing the calculation accuracy of this method are the assumption of constant producing reserves and the viscosity difference between the polymer solution during the laboratory measurement of relative permeability curves and the one in the real strata.