Hydration mechanism of cement in natural gas hydrate layer regulated by dodecanol @ spherulite-type calcium carbonate phase change composite materials

At present, the phase change materials used in the cementing slurry of natural gas hydrate (NGH) layer only pursue to meet the technical performance, and lack of comprehensive and in-depth research on the influence of cement hydration mechanism. In this study, a composite phase change material (FY) with spherulite-type calcium carbonate as the shell and dodecanol (DA) as the heat controlling unit was designed and prepared based on the exothermic hydration law of high early strength cement slurry. A comparative investigation was performed utilizing semi-adiabatic and isothermal calorimetry to investigate the influence of nano-calcium carbonate (NC), DA, and FY on the hydration kinetics and mechanism of cement. The hydration of cement was assessed both qualitatively and quantitatively using the XRD-Rietveld method and thermogravimetric analysis (TG/DTG). An investigation was conducted on the product evolution law and the impact of FY on the compressive strength of cement pastes. The findings indicated that FY had no impact on the cement hydration process. However, it did boost the hydration effect during the NG and I stages while weakening the hydration effect during the D stage. FY enhances the hydration process of C3S and C2S, decreases the formation of AFt, and stimulates the formation of CH and amorphous hydration products. Incorporating 0.5 wt% FY content effectively controls the release of heat produced during the hydration process of cement and ensures that the cement achieves a compressive strength of above 7.0 MPa within a period of 48 hours. The results of the experiments to evaluate the thermal stability of NGH show that G0.5 can be used to prevent the decomposition of NGH during the cementing of NGH layers. This study offers a significant theoretical and experimental foundation for the advancement and design of cementing materials and low-negative temperature cementing materials for natural gas hydrate layers. •The FY with spherulite-type calcium carbonate as shell and DA as core material was prepared.•The hydration mechanism of cement mixed with FY is NG-I-D.•FY strengthens the hydration effect of NG、I stages, but weakens D stages.•It is proved by direct experiment that FY can prevent the dissociation of NGH.