Experimental Study on Heat Transfer During Cement Slurry Hydration Using a Full-Scale Integrity Device

The integrity of the cement sheath and its interfacial bonding with the casing and formation are critical for zonal isolation in oil and gas wells. During cement hydration, heat released by chemical reactions induces thermal expansion of the casing, which may compromise the cement-casing interface bonding strength. This study constructed a full-scale wellbore assembly using 244.5 mm and 139.7 mm diameter casings, with cement slurry pumped into the annular space. A Fiber Bragg Grating (FBG) sensing system was employed to continuously monitor the temperature propagation and casing deformation dynamics throughout the hydration period. Experimental results revealed that annular gaps of 40 mm and 21 mm corresponded to maximum hydration-induced peak temperature rises of 18 °C and 8 °C, respectively. Under adiabatic conditions, the peak temperature rise reached 18 °C, compared to 9 °C in ambient conditions. Furthermore, for cement slurry with densities of 1.90 g/cm3 and 1.45 g/cm3, the recorded maximum temperature elevations were 18 °C and 10 °C, respectively. Strain optical fibers mounted on the inner casing enabled real-time quantification of external surface deformation. Specifically, under adiabatic conditions, a 9 °C temperature rise induced 8.5 μm of circumferential expansion on the casing outer surface, a direct manifestation of thermal-mechanical coupling effects. These systematic experimental findings quantify the thermal-mechanical coupling mechanisms during cement hydration, establish a robust experimental framework for characterizing hydration behavior under full-scale wellbore conditions, and thereby provide actionable guidelines for optimizing cement-casing bonding quality and ensuring long-term wellbore integrity in complex downhole environments.