AI-Aided Design of Carbonated Ductile Well Cement for Enhanced Recovery.

The long-term integrity of wellbores in enhanced oil recovery and enhanced gas recovery is critically dependent on the mechanical resilience of the cement sheath against tensile subsurface loads. This study developed a series of mix designs for ductile well cements using American Petroleum Institute Class H cement, silica flour, and fly ash and reinforced with polyethylene fibers to address the inherent brittleness of traditional oil well cements. The mechanical behavior and microstructural evolution of the composites were evaluated under normal/ambient and carbonation (10% CO2) curing conditions using uniaxial tensile testing, thermogravimetric analysis, and X-ray diffraction. Results indicated that PE fiber reinforcement transformed the failure mechanism from brittle fracture to ductile strain hardening, achieving a peak tensile ductility of 6.3% in the ternary blend after 7 days of normal curing. Carbonation curing accelerated hydration kinetics and matrix densification through extensive calcite precipitation, resulting in a CO2 uptake of 17.4 wt % by 28 days. While matrix densification limited the strain capacity to approximately 4%, carbonation curing stabilized the strain-hardening behavior across all test ages, effectively preventing the late-age embrittlement observed in air-cured specimens. An interpretable supervised machine learning framework was further employed to establish quantitative links between hydration and carbonation-driven microstructural evolution and the resulting strength and ductility. These findings demonstrate that fiber-reinforced Class H composites offer huge potential to improve zonal isolation and circular economy viability in CO2-rich subsurface environments.