Investigating the use of class C flyash-based geopolymer cement as a potential alternative to Portland cement to seal CO₂ storage wells

Capturing emitted carbon dioxide from the source of emission and storing it underground is one effective way to reduce the amount of CO2 in the atmosphere and is called carbon capture and storage (CCS). For the successful CCS project, it is necessary to ensure long term storage of injected CO2 inside these selected reservoirs. Portland cement used to cast wells in these reservoirs degrade in CO2 environment and can create migration path for leakage of CO2. The aim of this study was to provide a comprehensive review about the problem, to propose a new geopolymer cement as an alternative to Portland cement, optimize geopolymer slurry for oil well cementing operations and compare the performance of both cement in CO2 environment. The chemical alterations of cement and its effect on the mechanical properties of the cement was analyzed and discussed. Additives used till now with cement to obtain CO2 resistant cement were discussed. Optimization of geopolymer cement slurry using different alkaline activator to flyash ratios, sodium silicate to sodium hydroxide ratios and sodium hydroxide concentrations was performed. The aim of this study was to obtain a formulation of class C flyash-based geopolymer slurry that can be used in oil well cementing purposes. The result concluded that optimized geopolymer slurry has higher strength, lower fluid loss, no free fluid and rheological properties same as Portland cement. Optimized geopolymer cement and Class H Portland cement were then exposed to CO2 environment at two different phases of CO2 for different duration. Variations in the density, strength, and surface of the cement cores were analyzed and compared. Class C flyash-based geopolymer performed better in CO2 environment than Portland cement. --Abstract, page iv