Pore-Scale Transport Dynamic Behavior of Microspheres and Their Mechanisms for Enhanced Oil Recovery

Polymer microsphere transport in porous media widely appears in oil field development. However, the migration and plugging mechanisms of the microspheres at the pore-throat scale need further study. In this paper, four pore-throat and one reservoir etching models were designed to simulate the pore throat distribution with different heterogeneities and real reservoir pore structures, respectively. The pore-throat matching relationship, dynamic transport behavior, and enhanced oil recovery (EOR) mechanisms of microspheres were clarified based on the injectivity and displacement experiments. The results show that microspheres will preferentially occupy larger pores and throats, showing obvious selective plugging characteristics. Taking the absence of microspheres entering and retention in the throat as the basis for the mismatch between microspheres and pore throats, the upper limits of the matching factors of the sectional model and the axial model are 1.21 and 1.47, respectively, which is consistent with the macroscopic matching results. Microspheres have a significant liquid flow diversion effect, which can force the solution flow into the unswept small throat area and simultaneously displace blind-end residual oil and film residual oil in the swept throats. Microspheres can further increase the oil recovery by 6.85% compared with polymer flooding through three mechanisms: increasing the injection pressure, plugging dominant channels, and further dispersing the continuous remaining oil. The impact of the heterogeneity of the microsphere particle size and reservoir pore throat structure on microsphere migration and EOR effects will be a future research topic.