Performance evaluation of low-grade calcined clay as a supplementary cementitious material for sustainable oil-well cementing

This study investigated the use of low-grade calcined clay (CC) as a supplementary cementitious material (SCM) for oil-well cementing to improve sustainability without compromising performance. High Sulfate Resistant (HSR) Class G cement was partially replaced with 10–80% CC by weight of cement (bwoc). Uniaxial compressive strengths under both distilled water and in synthetic formation water (FW) curing, life cycle CO₂ emissions, and environmental impact were assessed and compared to those of control slurry prepared with pristine class G cement (100% class G cement without calcined clay replacement). The specimens were cured at 70°C in distilled water and FW. Results revealed that up to 60% CC replacement maintained comparable strength to the control slurry in distilled water, whereas 40% CC provided the maximum compressive strength in FW. Optimal performance occurred at 50% CC, achieving a 28% strength increase under FW curing. Life cycle assessment showed a 46.3% reduction in CO₂ emissions and a 58% lower environmental impact factor. The results indicate that CC can significantly enhance the mechanical performance and sustainability of oil-well cements in saline environments.