Thermo- and CO2-triggered viscosifying of aqueous copolymer solutions for gas channeling control during water-alternating-CO2 flooding

Water-alternating-CO 2 gas (WAG) flooding is a common technique to enhance oil recovery via improving CO 2 sweep efficiency, but serious gas channeling may still occur, especially in reservoirs with strong heterogeneity, due to a poor blocking capacity of aqueous slugs to the “channeling” pathway induced by their low viscosity. Herein, a copolymer whose aqueous solution viscosity can be increased by both heat and CO 2 was developed and added into the aqueous slug to control gas channeling and increase oil recovery during enhanced WAG processes. The copolymer was synthesized by grafting poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) onto the triblock copolymer, Pluronic F127, PEO 100 -PPO 65 -PEO 100 . The aqueous copolymer solutions can be thickened/gelled by heating due to the formation of micelles as the physical cross-link and their entanglements even at a concentration as low as 0.2 wt%, and viscosified by bubbling CO 2 thanks to expanded copolymer coils caused by electrostatic repulsion-induced chain extension of protonated PDMAEMA chains. Notably, thermo- and CO 2 -triggered viscosifying can work synergistically and they are completely reversible upon cyclically heating/cooling the copolymer solutions and bubbling/removing CO 2 into/from the aqueous phase, respectively. In WAG flooding tests using two parallel cores, gas channeling was mitigated by blocking high-permeability cores due to in-situ thermo-induced gelation and CO 2 -triggered thickening of copolymer slugs, thus diverting chase fluids into unswept low-permeability cores and enhancing 21–22% total oil recovery than the conventional and HAPM-enhanced WAG modes. Importantly, owing to the characteristics of low initial viscosity, single component, and thermo-gelation, this dually-responsive copolymer possesses high injectivity and satisfactory gelation control. This work could enlighten the design of novel dual/multiple stimuli-thickening polymers used for channeling control and enhanced oil recovery.