Experimental Investigation of a Polymer-Enhanced N2 Foam Performance for Enhanced Oil Recovery

The Bohai oilfield is a typical common heavy oil reservoir with high water cut after long-term water injection development. Considering the characteristics of selective plugging, polymer-enhanced foam (AOS–DYG) flooding was adopted in this study as a subsequent enhanced oil recovery (EOR) technology in the Bohai Sea. A polymer can promote foam stability by reducing the foam drainage rate and enhancing interfacial adsorption behavior. As a result of its low cost and abundant sources, nitrogen is selected as the air source of foam in this paper. The interaction between the polymer DYG and the surfactant AOS was clarified from the aspects of surface adsorption properties, surface dilated rheological properties, bulk phase rheological properties, and micromorphology. That is, the addition of polymer can increase the thickening ability of the foam-based liquid phase, the thickness of the liquid film, and the strength of the gas–liquid interface adsorption layer, all of which dramatically improve the stability of the foam. The core displacement test results further confirmed that the AOS–DYG foam displaced an excellent mobility control ability in porous media. When the foam mass (gas–liquid ratio) was 70% and the injection flow rate was 1 mL/min, the resistance factor and residual resistance factor at 2264.7 mD reached 246.11 and 127.33, respectively. With an increased core permeability, the oil displacement performance of the AOS–DYG foam increased. The enhanced oil recovery (EOR) of the 0.4 PV AOS–DYG foam in the 2547.8 mD core reached 32.19%, demonstrating an outstanding oil displacement capacity. The findings of the investigation supported the potential application of the AOS–DYG foam in EOR.