Research on the Construction and Performance of Low-Density Cement Slurry Systems for Deep and Ultra-Deep Well Cementing

Cementing long intervals in deep and ultra-deep wells faces numerous challenges. For instance, high bottom hole temperatures lead to poor cement slurry stability and long-term strength decline. The large length of the cementing interval results in a significant temperature difference, making the top of the cement column prone to excessive retardation. Moreover, the low bearing capacity of the open hole section causes easy leakage problems. To solve these problems a low-density cement slurry system suitable for high-temperature and large-temperature difference conditions with not declining long-term strength was successfully developed. This system was achieved by selecting high-temperature and high-pressure resistant light-weight materials, high-temperature anti-decline materials, and high-temperature resistant additives, and conducting an optimized design for close packing. The density of this system ranges from 1.40 to 1.50 g/cm3. Under the conditions of 160 °C and 140 MPa, it exhibits good high-temperature stability, with no free fluid and a density difference between the top and bottom of ≤0.03 g/cm3. Its thickening time can be linearly adjusted. The fluid loss is less than 50 mL. In a large-temperature difference environment with a top temperature of 60 ℃, it gains strength within 24 h, and the compressive strength exceeds 3.5 MPa after 48 h. After 30 days of curing at astatic temperature of 180 ℃ for the slurry, no strength decline is observed. Considering all its performance indicators, this system meets the technical requirements for ultra-high temperature cementing and provides strong technical support for deep and ultra-deep well cementing projects.