Experimental Investigation of Silica Fume as a Cement Extender for Liner Cementing in Iranian Oil/Gas Wells

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 (SiO2). 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.