Synthesis and Evaluation of Self-Decomposing and Recrosslinking Gel for Controlling CO ₂ Gas Channeling and Leakage in Deep Fractures

Gels have been developed to plug gas channeling and leakage problems during CO2 flooding and storage. Single materials are insufficient to plug cracks of different scales. This work overcomes the shortcomings of water-absorbing and swelling particles that are difficult to enter the interior of microcracks for plugging. Utilizing the novel temperature-sensitive cross-linkers polyethylene glycol diacrylate (PEGDA) and chromium acetate (CrAc) to form a composite cross-linking agent, and introducing the hydrophobic monomer butyl acrylate (BA), a gel particle capable of decomposition and recrosslinking underground was synthesized. This can enter the interior of microcracks and recrosslink to form a mechanically stable blocky gel, thereby controlling CO2 leakage and gas channeling. Experimental results show that the successful synthesis of D-RPPG and the introduction of characteristic elements were confirmed by Fourier transform infrared (FT-IR) and energy dispersive spectrometer (EDS), while swelling kinetics prove that the recrosslinking property only occurs above 65 °C. When 2% D-RPPG + 0.14% PEI + 0.02% nano-SiO2 are added, the gel strength is H, and the viscosity is still 486.4 mPa·s at high shear rates. It exhibits good stability after 60 days in a CO2 environment, and the increased viscoelasticity endows it with the ability to expand, deform, migrate, and plug in microfractures. After gelation in the core fractures, the breakthrough pressure gradient of CO2 increased to 12.2 MPa/m, and the oil recovery rate increased by 21.25%. All the work shows that D-RPPG has good application prospects in the field of multistage control of CO2 capture, utilization, and storage (CCUS) in fractured reservoirs.