Traditional polymer flooding technology has been widely used and obtained remarkable effect of increasing oil. However, in its later stage, the "entry profile inversion" phenomenon occurs inevitably, which seriously affects the development effect. To solve this problem, the micro-nano oil-displacement system has been developed in recentlt years. Due to its excellent performance and advanced mechanism, it can slow down the process of profile inversion, and achieve the goal of expanding swept volume and enhancing oil recovery substantially.

This novel system consists of micro-nano particles and carrier fluid. When migrating in porous media, it shows the unique motion feature of "trapping, deformation, migration", which froms Effective plugging and increases injection pressure. Meanwhile, carrier fluid is forced to enter the small pore with remaining oil, which increases oil production. Therefore, in this paper, reservoir adaptability evaluation, migration characteristics of micro-nano oil-displacement system (MNS) is tested by using the microfluidic technology and 3D Printing technology. On this basis, by adopting CT tomography technology, its oil displacement mechanism is further explored. Furthermore, the typical field application case is analyzed.

Results show that, the appearance of MNS is spherical particles, and it has good expansibility. Based on the reservoir adaptability test results, the matching relationship chart between MNS particle size and reservoir rock pore throat size can be obtained, which laid a good foundation for field trail scheme design. From micro experiments, MNS particles are prone to come into the larger pore with low flow resistance, which forms bridge blockage. Working together with carrier fluid, they can significantly enhance crude oil recovery. Furthermore, by adopting CT scanning devices, the percolation law of MNS in porous media and micro oil displacement mechanism is analyzed. During the experiment process, MNS particles presents the motion feature of "migration, trapping, and deformation", to realize deep fluid diversion and expand swept volume. From 3D macro experiment, MNS has strong transport ability in the core pore and good shear resistance. Lastly, two typical application cases are introduced and analyzed, which all obtained great success.

Through interdisciplinary innovative research methods, the performance evaluation, oil displacement mechanism and field trail of MNS is explored, which proves its progressiveness and superiority. The research results provide theoretical basis and technical support for this technology to enhance oil recovery significantly.

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