CO ₂ ‐Responsive Supramolecular Polymer–Surfactant System Enabled by Competitive Host–Guest Occupancy for Enhanced Oil Recovery in Low‐Permeab

ABSTRACT

Conventional polymer–surfactant flooding systems often suffer from poor injectivity, severe adsorption loss, and insufficient late‐stage mobility control in low‐permeability reservoirs. Herein, a CO ₂ ‐responsive supramolecular polymer–surfactant system, HXG‐BZI, was developed through competitive host–guest occupancy and pH‐triggered reconstruction. The system consists of β‐cyclodextrin‐grafted polyacrylamide, adamantane‐modified xanthan gum, and a benzimidazole‐based responsive surfactant. Before stimulation, BZI‐S preferentially occupies β‐CD cavities, weakening the host–guest network and maintaining low viscosity for favorable injectivity. Upon CO ₂ stimulation or acidification, protonated BZI‐S is released from the host sites, enabling recovery of HPAM‐CD/XG‐AD crosslinking while enhancing surfactant aggregation and interfacial activity. Characterization results confirm that the benzimidazole headgroup is the key responsive site, and acidification markedly reduces the critical aggregation concentration of BZI‐S. The HXG‐BZI system undergoes pronounced rheological and multiscale aggregation reconstruction. After CO ₂ triggering, mineral adsorption decreases by approximately 73% compared with CTAB and 68% compared with the untriggered system, while oil–water interfacial tension reaches 10 ⁻³ –10 ⁻⁴ mN·m ⁻¹ under saline conditions. Core flooding in 5 mD cores, including newly added oil displacement tests at 80°C, further confirms its transition from low‐resistance injection to high‐resistance flow regulation, providing a promising strategy for responsive chemical flooding in low‐permeability reservoirs.