Based on the characteristics of the large scope permeability distribution, and the joint action of the seepage law for both low permeability and medium to high permeability, aiming at the problem of the recovery restriction for low permeability points caused by the start-up pressure, the influence of the start-up pressure gradient of low permeability points on the sweep coefficient is studied by the numerical simulations. Also, by coupling the start-up pressure gradient and the displacement pressure distribution for the low permeability point, the correction method for the sweep efficiency is established. Result shows that the lower the reservoir permeability and the higher the permeability variation, the greater the influence of the start-up pressure of the low permeability points on the sweep coefficient. Taking the M oil reservoir in the Middle East as an example, the application analysis is carried out. When the reservoir permeability is between 5~35×10^-3 μm² and the permeability variation is between 0.6~0.8, the range of the correction coefficient is about 0.75~0.99, which in turn can correct the calculation of the sweep efficiency in the industry standards.

sweep efficiency  /  porous carbonate reservoir  /  low permeability points  /  start-up pressure gradient