CO2-responsive system for preventing gas channeling during CO2 flooding in low permeability reservoirs

At present, CO₂ flooding is extensively used in low-permeability reservoirs to enhance oil recovery (EOR). However, due to the serious heterogeneity of the formation, the gas is prone to escape along large pores during CO₂ flooding. Conventional CO₂ anti-channeling systems have some defects such as poor stability, weak retention capacity and inferior plugging effect. Therefore, it is critical to develop a novel type of CO₂ anti-channeling system for low-permeability reservoirs. Herein, four kinds of systems with amine groups are tested to identify the most effective CO₂-responsive system, which consists of poloxamer, dimethylaminoethyl acrylate, nano carbon powder, acrylamide and initiator. Subsequently, physicochemical properties of the optimum system are researched systematically by rheological experiments, CO₂-responsive processes and structural characterization. The results indicate that the viscosity of the system increases from 4.2 mPa s to approximately 67.8 mPa s as a result of increasing temperature and CO₂ injection. Meanwhile it can be reversibly cycled between low viscosity and high viscosity by alternately introducing and removing CO₂, which indicates the gas response behavior of the system is reversible. Furthermore, the plugging performance and EOR are evaluated using low permeability cores. The experiments demonstrate that the system can effectively restrain gas channeling and enhance recovery factor by as high as 22 % - significantly outperforming conventional water-alternating-gas (WAG) flooding which provided only a 10.62 % enhancement under comparable conditions. We expect our work can provide a new system and method for CO₂ anti-channeling in low-permeability reservoirs.