Percolation Mechanism and Cross-Scale Coupling Mechanism of Micro-Nano Dispersion Systems

Abstract Although polymer flooding technology has been widely applied and demonstrated remarkable effectiveness in oil recovery enhancement, the "injection profile inversion" phenomenon inevitably emerges during its later stages, significantly impairing development efficiency. To address this challenge, the Micro-Nano dispersion system has been developed as a novel enhanced oil recovery (EOR) technique in recent years. Owing to its superior performance and innovative mechanism, this system can effectively slow down the evolution of profile inversion while achieving deep fluid diversion and expanding swept volume. The Micro-Nano dispersion system consists of solid particles and a carrier fluid. After entering porous media, it exhibits the characteristic behavior of "plugging large pores while leaving small pores open." First, experimental techniques such as microfluidics (lab-on-a-chip), low-field nuclear magnetic resonance (NMR), combined with pore-scale microscopic physical simulations and three-dimensional macroscopic physical simulations, are employed to elucidate the reservoir adaptability, transport and migration behavior, and microscopic particle migration mechanisms of the Micro-Nano dispersion system in porous media, as well as to reveal the microscopic mechanisms responsible for flow resistance enhancement. Subsequently, based on three-dimensional physical simulations and theoretical analysis, the fluid diversion capability and synergistic enhancement mechanisms of the Micro-Nano dispersion system in heterogeneous reservoirs are quantitatively characterized. Furthermore, typical field application cases are analyzed. The results demonstrate that the Micro-Nano dispersion system exhibits excellent performance and favorable transport behavior in porous media. Reservoir adaptability evaluation reveals a clear matching relationship between particle size distribution and core pore-throat characteristics, which provides a solid theoretical and practical basis for the design and optimization of field application schemes. Microfluidic experiments are conducted to investigate the microscopic particle migration mechanisms within pore throats. The results indicate that, during the injection of the Micro-Nano dispersion system into core samples, particles preferentially migrate into and selectively plug larger pores in high-permeability layers. Consequently, the carrier fluid is effectively diverted into smaller pores and low-permeability regions to displace the remaining oil. This cooperative interaction between particles and carrier fluid enhances sweep efficiency while avoiding permanent pore blockage or damage to the reservoir. Macroscopic physical simulation experiments further confirm that the Micro-Nano dispersion system can effectively regulate fluid flow paths, strengthen deep profile control, and ultimately improve oil recovery. Moreover, when combined with other oil displacement agents, the incremental oil recovery can be further enhanced due to synergistic effects. Finally, this flooding technology has been successfully applied in multiple oilfields. Using interdisciplinary and innovative research methods, the oil displacement mechanisms and field performance of the Micro-Nano dispersion system are investigated, demonstrating its technological advancement and superiority. The results provide a solid theoretical basis and technical support for significantly enhancing oil recovery.