Hybrid Nano-Modified Cementitious Systems for Enhanced Oil-Well Cement Performance Under HPHT Conditions

Ibrahim Abdulwahhab Atiyah (Department of Materials Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045)
Ali A. Salman (Department of Materials Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045)
Dalia A. Rasool (Department of Materials Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045)
Ahmed S. Abbas (Department of Civil Engineering, College of Engineering, Al-Mustafa University, Baghdad 10045)
Mohammed Ali Abdulrehman (1) Department of Materials Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045, Iraq. 3) School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Nibong Tebal 14300)
Ali M. Flayyih (Department of Materials Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045)
Kadhim K. Resan (Department of Materials Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045)
Samer S. Abdulhussein (Department of Civil Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045)

Civil Engineering Journal
Vol. 12 No. 8 (2026): August

Class G oil-well cement exhibits compressive strength retrogression, high permeability, and poor chemical resistance under HPHT wellbore conditions, thereby posing risks to effective zonal isolation. This research explores hybrid nano-modified supplementary cementitious systems as a possible sustainable alternative to conventional systems. Four different modified mixes, including silica flour–fly ash–nano-silica, slag–fly ash–nano-silica, and latex–silica fume–nano-silica systems, were compared with neat Class G cement. The specimens were cured under HPHT conditions, ranging from 90 to 120 °C at 15 MPa for up to 90 days, and were also subjected to thermal cycling and CO₂/sulfate environments. They were analyzed using methods such as compressive strength testing, gas permeability testing, XRD, SEM, TGA, MIP, micro-CT, and nano-indentation. Neat cement showed retrogressive compressive strength behavior and high permeability, while the hybrid systems maintained more than 90% of their strength, developed compressive strength higher than 40 MPa, and showed lower permeability below 0.05 mD. From a microstructural perspective, portlandite depletion, refined pores smaller than 60 nm, and increased tortuosity of the pore network can explain these improved properties. The originality of this research lies in the comprehensive analysis of hybrid nano-modified SCM systems under HPHT, thermal cycling, and chemical exposure environments.