Effects of C3A and C3S with gypsums on the hydration of oil well cement under hydrothermal curing

Tricalcium aluminate (C 3 A) and tricalcium silicate (C 3 S) with gypsums play an important role in the hydration of oil well cement. This study aims to assess the influence of C 3 S and C 3 A with various gypsums on the hydration of oil well cement at 30, 50, and 80 °C through the analyses of hydration heat evolution by isothermal calorimetry analysis, setting and thickening times, strength, and hydration products by X-ray diffraction. The result reveals that C 3 A hydrates, in the presence of gypsums, rapidly at 80 °C to produce the C 3 AH 6 phase leading to higher heat evolution. The conversion of AFt to AFm is observed in oil well cement paste at 50 °C. An increase in C 3 A leads to an increase in compressive strength and a decrease in permeability at 80 °C. An increase of C 3 S leads to the reduction of cumulative heat evolution and early compressive strength before 28 d. Gypsums shorten cement setting and thickening times opposite to the commonly known retardation effect due to the lower content of C 3 A and its acceleration on C 3 S hydration. Dihydrate and hemihydrate gypsums show a greater promotion effect on strength at 30 and 50 °C, while anhydrous gypsum presents a greater enhancing effect at 80 °C. Gypsum increases the permeability while the others show an unobvious effect at 80 °C.