Effect of Ultrafine Calcium Silicate on the Mechanical Properties of Oil Well Cement-Based Composite at Low Temperature

A low-temperature environment will reduce the hydration rate of oil well cement-based composites, resulting in the slow development of mechanical strength, which cannot meet the requirements of cementing operations. In order to improve the early strength of cement paste under low temperature, the influence of ultrafine calcium silicate powder on the rheological properties, water loss, thickening time and permeability of oil well cement-based composites was evaluated. The compressive strength, flexural strength and impact strength of cement paste with different contents of ultrafine calcium silicate were studied. The hydration process and microstructure of cement paste were analyzed by hydration heat measurement system, X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental results show that the ultrafine calcium silicate has a certain impact on the rheology and thickening time of cement slurry, and dispersants and retarders are required to adjust these properties when it is used. The ultrafine calcium silicate can improve the stability of cement slurry and reduce water loss and permeability. In addition, under the condition of curing at 20 °C for 24 h, the compressive strength, flexural strength and impact strength of cement paste with 8% ultrafine calcium silicate content increased by 243.0%, 278.5% and 66.3%, respectively, compared with the pure cement paste. The hydration of cement slurry is accelerated by ultrafine calcium silicate, the hydration temperature is enhanced and the heat release of hydration is increased. The ultrafine calcium silicate improves the formation degree of hydration products and makes the structure of cement paste more compact. The research results help to design a low-temperature and early-strength cement slurry system.