Evaluation of an Oxygen-Reduced Air Flooding Plugging System and Its Injection Method in the Honghe Oilfield

Oil recovery in a pilot test of gas flooding in the Honghe oilfield was greatly affected by the presence of fractures of various scales and the limited effect of a single plugging system. To elucidate the gas channeling behavior and identify the optimal injection method of oxygen-reduced air flooding in fractured tight oil reservoirs, foam and gel systems were selected to plug small and large fractures, respectively. Various methods of injecting oxygen-reduced air were studied through parallel core flooding tests to compare the gas channeling characteristics and changes in oil recovery during different plugging and displacement processes. Experimental methods including Waring blender, scanning electron microscopy, temperature resistance evaluation, and plugging performance and core flow evaluation were used in this study. The experimental results showed that the optimized FC-2 foam had the best foaming ability and half-life for the gas/liquid ratio of 1:1 and the mass fraction of 0.3%. In addition, the prepared gel had a complex and dense three-dimensional network structure, and the plugging rate was 98.17%. Finally, a displacement experiment showed that the combination of water, gel, FC-2 foam plugging system, and 5% oxygen-reduced air had the best plugging effect and gave the highest oil recovery. Compared with injecting oxygen-reduced air only, oil recovery from the small fracture core, large fracture core, and parallel core were improved by 19.71, 14.66, and 17.53%, respectively.

Automated summary

This study investigated the gas channeling behavior in fractured tight oil reservoirs during oxygen-reduced air flooding and evaluated the effects of different plugging and displacement processes on oil recovery. Experimental results showed that the optimized foam and gel systems effectively plugged fractures and improved oil recovery. The combination of water, gel, FC-2 foam plugging system, and 5% oxygen-reduced air had the best plugging effect and highest oil recovery.