Influence of Early Hydration Process on the Hydrostatic Pressure Change of Cement Pastes at Different Temperatures.

In cementing operations, a rapid decrease in the hydrostatic pressure of cement paste is one of the main causes of early gas channeling. In response to this issue, tests were conducted on the variation in the hydrostatic pressure of cement paste over time at different temperatures (30 °C-180 °C), and it was found that the curve of its rapid decrease time point with temperature change conforms to the Boltzmann function. The relationship between the early hydration process and the microstructure of paste at 90 and 150 °C, as well as the changes in hydrostatic pressure, was studied using X-ray powder diffraction, thermogravimetry, and scanning electron microscopy. The results show that the hydrostatic pressure curve of the paste shows a trend of first stabilization and then rapidly decreasing at medium and low temperatures (30 and 90 °C). At high temperatures (150 °C), the pressure curve initially increases until stabilization, enters a stable period, and finally rapidly decreases. In the early stage of hydration induction, there is a large amount of free water between hydration products, and the hydrostatic pressure of the paste remains stable. In the process of hydrostatic pressure reduction, the microstructure of the paste develops from the particle hydration products to a "gel framework", which isolates the pressure transfer of part of the free water. During the acceleration period of hydration, the hydration products enhance the "framework" and reduce the porosity of the paste, completely cutting off the transmission of water pressure, resulting in a rapid decrease in the hydrostatic pressure of the paste. A method for predicting the rapid decrease in hydrostatic pressure of the paste was proposed using the hydration reaction process.