CO2 Conformance Control and Carbon Storage Performance of Particle Gels in Fractured Reservoirs Using Nuclear Magnetic Resonance Methods

Summary Particle gels, as high-efficiency materials for large flow channels like fractures, demonstrate significant potential in controlling CO2 channeling and enhancing carbon sequestration during CO2 flooding in fractured reservoirs. While preformed particle gels (PPGs) and flexible particles (FPs) represent two prevalent conformance control agents, their comparative performance in CO2 diversion remains poorly understood. This study evaluated these two structurally distinct particle gels through static swelling tests, rheological analyses, fracture transport/plugging experiments, and core dynamic plugging tests. Nuclear magnetic resonance (NMR) was also used to elucidate the microscale mechanisms of CO2 channeling control and sequestration enhancement. Results show that PPGs exhibited a swelling ratio of 36.15 in brine but underwent dehydration after 7-day CO2 exposure. In contrast, FPs exhibited no aqueous swelling but demonstrated a CO2-induced expansion ratio of 1.13 with reduced viscoelasticity. Both gels maintained excellent injectivity (> 1 mm fractures, i.e., >0.0394 in fractures) when brine-transported though coreflooding confirmed FPs’ superior CO2 channeling control capability. Innovatively, NMR T2 analysis provided pore-scale evidence of enhanced carbon sequestration mechanisms, FPs created stronger fracture blockages with less core matrix damage (e.g., avoiding water blocking caused by PPG dehydration), enabling FP selection as the optimal CO2 conformance agent. Notably, storage modulus (G’) showed no direct correlation with plugging strength. This work established a theoretical framework for selecting optimal particle gels to mitigate CO2 channeling and enhance carbon storage efficiency in fractured reservoirs.