Abstract: Most of the marine sandstone oil fields in the western part of the South China Sea have entered the middle-and high-water cut stage. The permeability of these reservoir changes constantly under the long term scouring effect. Because it is difficult to quantitatively characterize and predict the dynamic variation in permeability of oil reservoirs during the extraction process by core displacement experiments, we analyzed the dynamic variation pattern of reservoir permeability during a waterflooding process. In this study, the flux at the preferred surface is used as an index to characterize the reservoir scouring strength. By analyzing the mechanism associated with the change in permeability and adapting it to rationalize the temporal variation in permeability of production and testing wells during the oil reservoir extraction process, we derived a logarithmic prediction formula that describes the change in permeability with varying surface flux. We further applied the equation in a wider range of applications and expanded the applicability of the logarithmic correlation. Finally, a high-ratio oil displacement experiment is designed and performed to validate the accuracy and scientific merits of the proposed logarithmic relationship between permeability and surface flux. This logarithmic relationship was found to work well in practical applications during the later stages of oil extraction in oil fields with high water content in the western part of the South China Sea.

Key words: marine sandstone oil fields, surface flux, scouring strength, temporal variation of permeability, high-ratio oil displacement experiment