Visualization of water channeling and displacement diversion by polymer gel treatment in 3D printed heterogeneous porous media

Abstract

Polymer gels are widely applied to increase the sweep efficiency in mature oil fields facing severe water channeling problems after years of water flooding. The formation of water channeling and successful polymer gel treatment are rooted in complex pore-scale displacement and diversion. Thus, accurate characterization of the pore space and direct visualization of the interior displacement processes in real reservoir rocks such as water flooding, polymer gel injection, and chase floods are crucial in determining the controlling mechanisms of water channeling and polymer gel diversion. In this study, 3D X-ray micro-computed tomography (μCT) was used to characterize the porous structures of three distinct levels in water-flooded reservoir sandstones. A heterogeneous digital model was designed, which comprised representative layers of the obtained porous structures. Then, 3D-printing technology was used to manufacture a transparent model based on the digital prototype. A series of displacement experiments were conducted in the printed model to directly visualize the flow behaviors in the actual pore geometries. In the experiments, the model was first saturated with white oil and flooded by formation water until the outlet discharged only the water phase. Then, an immediately prepared polymer gel was injected. After three days of gelation, an antidilution polymer was injected to sweep the residual oil in the model. Finally, a surfactant flooding agent was injected designed to further increase the oil recovery. The entire four-step displacement process was directly visualized, and the saturation of each injection and the oil recovery were calculated. During water flooding, preferential flooding channels formed in the highest water-flooded porous layers due to the low viscosity ratio between the injected formation water and the displaced white oil, as well as the permeability contrast in the heterogeneous model. The injected polymer gel mainly followed the preferential flooding channels because of the low resistance force in these channels. After gelation, the polymer gel blocked the main preferential channels and diverted the chase floods to nearby pores. A desirable diversion of the polymer gel highly depends on its propagation path during injection and effective blocking after gelation. Experimental visualization and displacement mechanism analysis indicate the efficacy of the flow diversion by the polymer gel treatment in the heterogeneous porous model. The results provide useful information on the displacement behavior in heterogeneous porous structures, and the conclusions apply to similarly scaled systems at the reservoir scale.