Effect of Aging on Class G High Sulfate-Resistant Oil Well Cement Under High Relative Air Humidity

Previous research on cement aging mainly focuses on construction cement, exploring the mechanisms through which aging conditions affect cement properties. However, the impact of aging on oil well cement remains understudied. Aging of cement under high-humidity conditions leads to significant alterations in its properties, indicating that the cement formulation needs to be adjusted to reduce the negative effects during cementing operations. The effect of aging on particle size, mineral composition, and early hydration behavior of oil well cement after 0, 7, 14, and 28 d at 90% relative humidity (±3%RH) and 25 °C (±2 °C) was investigated. The results showed that, during the aging process, the uptake of H2O and CO2 from the surrounding atmosphere by cement leads to slight hydration. This process was associated with a reduction in the specific surface area and surface energy. The contents of hydration products ettringite (AFt) and calcium hydroxide (CH) increased, whereas the amounts of C3S and C3A decreased. Consequently, the early hydration rate of cement decreased along with a reduction in the cumulative heat release. As the aging time increased, the compressive strength and thickening time of the cement pastes decreased, and the rheological properties deteriorated. Under the experimental temperature and humidity conditions, the permissible aging time without significant deterioration should not exceed 7 d, with a maximum permissible aging time of 14 d.