Microscopic plugging adjustment mechanism in a novel heterogeneous combined flooding system

In this study, novel pre-crosslinked gel particles were synthesized to form a new heterogeneous composite system with a weak alkaline-surfactant-polymer (ASP) system. The microscopic visualization model is used for oil flooding and macroscopic core flooding experiments and advanced testing methods to describe the microscopic morphology of the pre-cross-linked gel particles and their retention state in the porous medium, revealing the microscopic plugging mechanism of the novel heterogeneous composite system in the porous medium. Scanning electron microscope images showed a uniform force on the pre-crosslinked gel particle network structure during the stressing process, with no mechanical weak points and improved tensile properties. The maximum pressure induced by the pre-cross-linked gel particles passing through the 0.5 mm diameter pore plate was 4.8 times higher than that of the conventional bulk particles. The elasticity factor of the pre-cross-linked gel particles was eight times higher than that of the conventional body expansion particles. Adding pre-cross-linked gel particles to the composite system improves the interfacial tension stability and effectively reduces the amount of chemicals under the same interfacial tension level. In a three-tube parallel core flooding experiment, the final heterogeneous composite flooding recovery after polymer flooding was 7.3% higher than that of ASP. The heterogeneous composite flooding system improves the recovery of crude oil after polymer flooding by blocking pore flow steering, wetting reversal, co-emulsification, and poly merging oil zone mechanisms. Thus, the implementation of heterogeneous composite flooding after polymer flooding can achieve the synergistic effect of blocking the dominant seepage channel and improving the oil washing efficiency, which can significantly improve the degree of remaining oil utilization. To clarify the microscopic blocking mechanism of the heterogeneous composite system, it is important to guide the development of post-polymer flooding composite flooding technology and research its microscopic flooding mechanism.