New Lightweight Cement Formulation for Shallow Oil and Gas Wells

The use of lightweight pozzolanic aggregates as partial replacement of cement results in low-density cement systems. Such systems ensure effective zonal isolation in zones where low equivalent circulating densities are required. However, low pozzolanic materials, such as fly ash and ground granulated blast furnace slag (GGBFS), have poor early-age strength development and long set times, especially when used in high volume, that is, exceeding 50% by weight of cement. The objective of this study is to develop a lightweight oil- and gas-well cement recipe with enhanced properties employing the synergism that exist among fly ash, GGBFS, and silica fume. The experimental work was per laboratory procedure outlined by American Petroleum Institute. Portland class G cement and the aluminosilicate materials were admixed in water to form a 13.5 ppg slurry. Chemical admixtures were used to facilitate the dissolution of reactive components in the pozzolanic materials and the hydration process. The experimental investigations were done at 150 ^°F and an ambient pressure of 1500 psi. The newly developed lightweight recipe exhibited excellent rheological and mechanical properties, having a wait-on-cement time for about 4 h and a 24 h sonic strength of 3116 psi, at 150 ^°F and 1500 psi. The thickening time was approximately 4 h (70 Bc). This slurry will be ideal in zones that would require a low hydrostatic slurry column and rapid gel strength development.