Silane-mediated organic–inorganic interfacial regulation improves deformation coordination and structural integrity of silica-rich oil well cement under hydrothermal conditions

Improving deformation coordination at interfacial regions is a potential strategy for maintaining the structural integrity of silica-rich oil well cement under high-temperature hydrothermal conditions. Amino silane (ASMR) was introduced to regulate organic–inorganic interfacial interactions. The macro- and micro-mechanical properties, volumetric deformation, pore structure, product evolution, surface chemical environments, strain distribution, and strength retention during extended hydrothermal curing were investigated. XRD results showed that ASMR did not fundamentally alter the principal hydrothermal product evolution path, while the TG-derived non-evaporable water estimates exhibited similar temperature-dependent evolution in both systems. XPS results indicated ASMR-derived N-containing species on the analyzed hydration-product surfaces and associated changes in the local surface chemical environment, while EDS mapping provided complementary information on the spatial occurrence of ASMR-derived N-containing species within the analyzed microstructural regions. After curing at 150, 180, and 200 °C, the strength of the blank oil well cement decreased from 50.4 MPa to 29.1 MPa, whereas the ASMR-modified system maintained a comparable strength of 29.6 MPa at 200 °C. The ultimate tensile strain increased from 678, 503, and 631 µε for the blank group to 1182, 1414, and 1378 µε for the modified group. Under 200 °C curing, the coefficient of variation of surface strain distribution after 48 h decreased from 1.33 to 0.83, and the strength retrogression rate from 2 to 28 d decreased from 40.1% to 16.6%. These results suggest that ASMR-mediated organic–inorganic interfacial regulation is associated with improved local deformation coordination, reduced expansion-induced strain localization, and mitigated strength retrogression.