Pressure-transient analysis of CO2 flooding based on a compositional method

•A compositional transient flow model of CO2 flooding is presented.•The transient pressure characteristic of CO2 flooding is analyzed.•The CO2 flood front can be found via the pressure derivative curve.•A numerical well test interpretation method can be established based on the model.

To find a reliable and inexpensive method to estimate miscibility and other reservoir parameters, as well as to monitor the CO2 flood progress, this paper proposed a transient flow model based on a compositional model that considers the wellbore storage effect, skin factor and multiple-contact processes. The model solution is obtained with the finite volume method and by performing pressure transient analysis. The results demonstrate that the pressure derivative curve of the swept area radial flow rises first and later declines slightly; the pressure derivative curve of the unswept area radial flow rises first and later becomes flat. The CO2 flood front can be recognized when the derivative curve begins to rise after it declines slightly in the swept area radial flow regime. A numerical well test interpretation method can be established based on the model used in this paper to estimate the permeability, miscibility, and formation damage and to monitor the CO2 flood progress.