Multiscale Study of Deepwater Cementing Cement: Integrating Thermally-Pressurized-Hydration Coupled Prediction Models with Fractal Analysis of Microstructures

In this study, we carry out modeling, validation and mechanism analysis for the complex multi-field coupling between cement paste temperature, pressure and hydration reaction during deepwater cementing. Based on the kinetic theory of cement slurry hydration reaction, a multi-field coupling model of wellbore-temperature-pressure during deepwater cementing is established, and the numerical solution of the coupled system is realized by using the difference method. The model aims to reveal the interaction mechanism between temperature, pressure and hydration reaction during the waiting period for curing, and provide theoretical prediction tools for engineering applications. In order to verify the accuracy and reliability of the proposed model, this study introduces the environmental scanning electron microscope (ESEM) experiment and combines it with the fractal dimension analysis method to quantitatively characterize the evolution of the microstructure of the cement paste during the solidification process, which realizes the effective extraction of the pore structure and microscopic information. By comparing the numerical calculation results of the model with the experimental data, the calculation results of the proposed multi-field coupling model are in good agreement with the experimental data, and the prediction accuracy meets the requirements of engineering practice. The conclusion of the study shows that the transient temperature and pressure changes significantly affect the hydration behavior of cement paste: the hydration reaction is accelerated under high temperature and high pressure, and the heat of hydration leads to a rapid increase in the temperature of the paste, while the change of temperature and pressure also causes an increase in permeability, which exacerbates the risk of gas migration. The low-temperature environment of deep water prolongs the curing cycle of cement paste, which poses a challenge to cementing safety. This work provides a new theoretical basis for the microstructure design of cementitious materials and the evaluation of cementing safety process through a combined macro-micro research approach.