Abstract:

Polymer flooding is one of the important means in enhancing oil recovery. Based on the physical process of polymer flooding, the well test model of three parts composite reservoir composed of Newtonian fluid/non-Newtonian power-law fluid/Newtonian fluid was established. The Laplace transform was used to obtain the analytical solution. The analytical solution of Laplace space was inverted to the real space by using Stehfest numerical inversion algorithm, and the double logarithmic theoretical curves of well test analysis describing the seepage characteristics of polymer flooding process were obtained. According to the characteristic of the derivative curve, four typical flow stages can be identified: the pure well bore effect stage, radial flow stage of inner part, polymer part and outer part. In the radial flow stage of inner part, the double logarithmic curves of the pressure derivative is a horizontal line with the value of 0.5. The larger the radius is, the longer the horizontal line will be. In radial flow stage of polymer part, the double logarithmic curves of the pressure derivative is a line with the slope of （1-n）/（3-n）. The smaller the power law index is, the greater the slope of the derivative curve will be. In the radial flow stage of outer part, the double logarithmic curves of the pressure derivative is a horizontal line with the value of 0.5M₁₃. The model can be used to analyse the effect of polymer flooding and guide the effective interpretation of well test data in polymer flooding reservoirs.

Key words: polymer flooding, composite reservoir, power-law index, Stehfest inversion, well test analysis