Rheological properties of Class F fly-ash based alkali-activated materials (AAMs) for oil and gas well cementing applications

Class F fly ash-based alkali activated materials (AAMs) have shown promising strength and durability properties for oil- and gas-well cementing applications. Furthermore, they provide a sustainable and cost-effective means to dispose of non-aqueous drilling fluids and replace ordinary Portland cements for cementing purposes. This paper investigates the rheological properties and thickening time behavior of AAMs prepared using four different Class F fly ashes (FA), with varying calcium oxide (CaO) contents, and sodium/potassium silicate activators. The effect of the addition of synthetic based mud (SBM) and polycarboxylate ether-based (PCE) dispersing agent on the rheology of AAMs was also quantified. Potassium silicate-based AAMs demonstrated appropriate viscosity and thickening times (4–9 h) for cementing deeper zones of oil and gas wells. Sodium silicate-based AAMs, although more viscous than potassium silicate-based AAMs, showed suitable thickening times (2–8 h) for shallow cementing jobs. Overall, it was demonstrated that AAMs could be tailored to obtain desirable rheological properties and thickening times by altering the Class F FA, varying the activating solution, and adding PCE and/or SBM.