Characterization of the dynamic heterogeneity during polymer flooding in reservoirs with stratified non-communicating layers

Heterogeneity affects the development performance greatly and, therefore, is an important property of the reservoir. The conventional method mainly takes permeability, which often does not change during the production process as the characterization parameter of heterogeneity. However. in polymer flooding, the injected polymer is more likely to enter the high-permeability zone with low resistance, which leads to the decrease of the resistance difference between the high and low-permeability zones. This non-uniform resistance due to the unbalanced distribution of polymer solution changes the heterogeneity of the reservoir dynamically, and it cannot be reflected by the current representation method. In this paper, a new parameter called "motivation coefficient" (I-P) is proposed, in which not only is the static permeability included, but also the dynamic parameters related with polymer property are taken into consideration, and the Gini coefficient of I-P (GC(IP)) is selected to represent the dynamic heterogeneity during polymer flooding. Then physical experiment and numerical simulations are done to study the variation law of dynamic heterogeneity during the polymer flooding. The results show that the dynamic heterogeneity is greatly improved after polymer injection. However, at the subsequent water flooding stage, the dynamic heterogeneity is more intensified when the whole polymer flooding process is over. Comprehensively considering the dynamic heterogeneity and development performance, the most favorable value of Gini coefficient of permeability is 0.6, and the best range of polymer concentration is from 0.1% to 0.15%. As for the slug size, large sizes are preferred if they are economically viable.