Iranian Journal of Chemical Engineering (IJChE)

Abstract Silica fume is a by-product of silicon metal or ferrosilicon alloys in smelters using electric arc furnaces. It consists of 85% to 95% amorphous silicon dioxide (SiO 2). Each individual particle of silica fume is spherical with average diameter 0.15-0.3 μm (100 times finer than cement particle); therefore its specific surface area is high. Silica fume particles are water wet and absorb excess water in cement slurry when cement slurry is extended by water. Silica fume thickens the cement slurry, so rheological properties are controlled by dispersants. In this paper, optimal concentration of silica fume and other additives for preparing 90 pcf cement slurry for liner cementing in one Iranian oilfield is determined. The criteria of designing slurry formulation are slurry density, rheological properties, fluid loss, free water, thickening time of cement slurry, and compressive strength and permeability of set cement. Finally, based on experimental results, the preferable slurry compositions are selected. This formulation can be used for cementing of oil and gas wells where moderate and light weight cement density is needed.

Abstract The ternary system of Portland cement-microsilica-limestone has been studied by investigating its set and strength behaviours. A number of different cementitious systems comprised of 0, 10, 15, 20, 25, and 30% limestone powder and 0, 4, 6, 8, 10, 12, 14, and 16% microsilica were designed and prepared. The cementitious systems were then characterized by determining their relative workability and measuring their initial and final setting times and also their 7- and 28-day compressive strengths using paste specimens prepared at a constant W/C-ratio of 0.38. Total 77-day shrinkage of the systems was also measured. The obtained results reveal that both 7- and 28-day compressive strengths increase with increasing microsilica up to 12% and decrease with increasing the percentage of limestone powder. A comparison of the results confirms the possibility of replacing Portland cement by a proportioned mixture of microsilica and limestone powder for enhancing the strength behaviour or producing composite cements containing relatively high proportions of limestone powder with no loss in 7- and 28-day compressive strengths compared to plain cement.