Remediating Caprock Integrity of Deep Saline Aquifers for Safe CO2 Geological Storage Using a CO2-Responsive Hybrid Gel with Delayed Gelation Time and Rock Adhesion

Abstract The long-term caprock security of geological CO2 storage in deep saline aquifers is threatened by the pressure buildup at caprock-reservoir interfaces. Conventional sealants often fail to reconcile injectability, deep propagation, and permanent sealing. This paper proposes injecting a CO2-responsive, long-term-stable, and flowable sealants into the overlying aquifer to create an impermeable flow-diverting barrier. The objective of this work is to design and fabricate this type of novel sealants and evaluate the performance in caprock remediation. Stiffen polysilicic acid (P(H2SiO3) was incorporated into soft AM/AMPS matrices to develop a CO2-responsive organic-inorganic hybrid P(AM-AMPS)-P(H2SiO3)/TA gel through dual-site stepwise cross-linking, with catechol-rich tannic acid (TA) providing robust caprock adhesion. The resulting P(AM-AMPS)-P(H2SiO3)/TA gel exhibited a gelation time of 350 h, a compressive strength of 4.06 MPa, and a caprock adhesion of 40.00 kPa. The P(AM-AMPS)-P(H2SiO3)/TA gel maintained integrity when exposed to 12.0 MPa scCO2 over 120 days. The CO2 breakthrough pressure drop gradients of the P(AM-AMPS)-P(H2SiO3)/TA gel were 54.0 MPa/m in fractures apertures of 1.0 mm, approximately 6.74-9.85 times higher than that of the reported sealing materials for CO2 leakage remediation. Continuous CO2 injection test showed that the P(AM-AMPS)-P(H2SiO3)/TA gel maintained a persistent CO2 pressure drop of 2.70 MPa over 30 days by firmly adhering to the subsurface-caprock and caprock-reservoir interfaces.