Study on Microscopic Distribution Characteristics of the Remaining Oil in Polymer-Flooded Reservoirs

Polymer flooding is an effective enhanced oil recovery (EOR) technology used in Daqing Oilfield. Microscopic distribution of remaining oil in polymer-flooded reservoirs is more complicated in comparison with waterflooded reservoirs. In this paper, UV excitation, frozen section-laser confocal technology, and three-dimensional reconstruction technology were employed to investigate the distribution law and occurrence state of the microscopic remaining oil in polymer-flooded Daqing Oilfield. With these methods, the occurrence states of the microscopic remaining oil distribution in different washing degrees and displacement locations were analyzed, and the remaining oil distribution before and after polymer flooding was compared quantitatively. The changes and microscopic distribution characteristics of crude oil components in the process of polymer flooding were clarified, and the relationship between clay minerals and the microscopic remaining oil distribution was discussed. Based on the statistical analysis of experimental results, the remaining oil of the free state decreases gradually, while the remaining oil of the bound state increases as the washing degree increases. In addition, the remaining oil in the distributary line is more enriched than the mainstream line after polymer flooding. Compared with waterflooding, the remaining oil of the free state becomes more, while the remaining oil of the bound state becomes less after polymer flooding. The frozen section-laser confocal experimental results also indicate that the proportion and distribution characteristics of the remaining oil components have been changed, and heavy components increase while light components decrease in the polymer-flooded stage. This research performs the quantized characterization and detailed analysis of remaining oil systematically and lays the foundation for remaining oil prediction and potential tapping in polymer-flooded reservoirs.