Hydration and degradation mechanism of sodium hexametaphosphate chemically bonded material under CO2 sequestration

Abstract

CCUS (Carbon Capture Utilization and Storage) technology is considered the most economical and feasible technology to significantly reduce CO2 emissions. The sealing integrity, especially degradation resistance, of cementing cement sheaths in CO2 sequestration wells plays an essential role in the efficient and long-term safe storage of CO2. This work applied various analytical methods to study the phosphate chemically bonded materials prepared by incorporating different dosages of phosphate into high alumina cement at 50 °C. Results show that the maximum slurry strength was achieved at the sodium hexametaphosphate dosage of 3%. The higher dosage of sodium hexametaphosphate generated more C-A-P-H gel phases in the cement matrix. The increase of capillary force caused by C-A-P-H gel during degradation will cause the cement stone to change from passive intrusion of CO2 to spontaneous imbibition, which deepens the intrusion of CO2. However, the C-A-P-H gel does not participate in the degradation reaction and prevents the degradation of the hydration products by CO2, thus not causing a reduction in the mechanical strength of the cement stone.