The relationship between the time-varying law of the hydrostatic pressureof cement slurry and the early hydration process

Annular channeling has seriously troubled deep oil and gas exploitation, and the reduction of hydrostatic pressure of cement slurry in the waiting stage is considered one of the main causes of early annular channeling. However, at present, there is still a lack of sufficient research on and understanding of the relationship between the time-varying law of hydrostatic pressure of cement slurry and the early hydration process in different well sections, especially in high-temperature well sections. Therefore, in this paper, a hydrostatic pressure measurement experiment of cement slurry at low temperature (50–90 °C) and high temperature (120–180 °C) was carried out using a self-developed hydrostatic pressure measurement device of cement slurry. Then, the cement slurry cured at 90 °C for 1–8 h was sampled by the freeze-drying method, and XRD and TG experiments were carried out. The results show that the hydrostatic curves of low and high temperatures both show a trend of rapid increase first, then remain stable, and then decrease rapidly. With an increase in temperature, the time of the stable and falling segments of the hydrostatic curve of the cement slurry gradually decreases. By fitting the rapid pressure drop time points of cement slurry at different temperatures, it can be determined that the rapid pressure drop time and temperature show a functional relationship. The XRD and TG results of different curing times at 90 °C were analyzed. It can be seen that in the early stage of the hydration induction period, the connection between cement particles is not close, and the hydrostatic pressure of the cement slurry column remains stable. As the hydration process enters the acceleration period, the cement particles crosslink with each other through hydration products to form a bridge structure, and the hydrostatic pressure of the cement paste begins to decrease. This shows that the pressure drop time can be controlled by regulating the hydration process to provide theoretical guidance for cement slurry preparation and slurry column design in cementing engineering.