Macro-micro matching limits of polymer microspheres with pore throats in enhanced oil recovery

Polymer microspheres can continue to migrate through the pore throats by the elastic deformation after plugging pore throats， achieving deep profile control and flooding in reservoirs. The successful application of polymer microspheres hinges on their excellent match with the reservoir， necessitating the study of their macroscopic core scale and microscopic pore-throat scale matching relationships. First， two sizes of polymer microspheres （MG-1 and MG-2） were synthesized， and injectivity experiments were conducted through long different permeability cores with intermediate pressure measurement points. The macroscopic matching characteristics between polymer microspheres and pore throats were identified through the three-stage pressure gradient curve patterns. Second， the pore-throat models were used to carry out microfluidic displacement experiments of polymer microspheres to evaluate the microscopic matching characteristics of polymer microspheres with pore throats based on their entry and retention status in throats at different scales. The matching patterns between polymer microspheres and cores can be divided into three types： end-face plugging， matching， and direct passage. Based on the pressure difference at the ends of the polymer microsphere injection and the subsequent water flooding， the upper limit of the macroscopic matching coefficient between MG-1 and pore throats was determined to be 1.3 to 1.4， with the optimal matching coefficient being 0.8 to 1.0. The microfluidic displacement results show that microspheres need to be under a certain pressure to enter smaller pores and throats. The maximum matching coefficients for MG-1 to enter and retain in cross-sectional and axial models are 1.21 and 1.47， respectively， corresponding to the optimal matching coefficient and upper limit of microscopic matching between MG-1 and pore throats. The macro-micro matching characteristics of polymer microspheres with pore throats are highly consistent. The error is caused by the high-pressure gradient in microfluidic displacement and the end-face effect in core flooding. Considering the macro and micro matching characteristics comprehensively， the optimal matching coefficient for MG-1 with pore throats is around 1.0， with an upper limit of about 1.4. The experimental results show that it is feasible to use microfluidic displacement experiments to replace complex core flooding experiments to evaluate the matching of polymer microspheres with pore throats.