Early Age Properties of Alkali-Activated Cement and Class G Cement under Different Saturation Conditions in Oil Well Applications

This experimental study evaluates the early-age properties of one-part alkali-activated cement (AAC) and class G cement (GC) under three subsurface curing conditions of water, brine, and carbon dioxide (CO2)-saturated water. The novel one-part AAC used in this study consist of fly ash and slag as the mineral precursors activated by a waste glass/sodium hydroxide-based solid alkali activator. The fresh and hardened properties of AAC and GC were characterised using rheology, strength, and microstructural tests. AAC showed relatively lower flow and setting time than GC under ambient conditions. Both the yield stress and plastic viscosity of AAC were reduced at elevated temperatures. AAC showed comparable strengths under water, higher strengths under brine, and lower strengths under CO2 saturation conditions compared to GC. Microstructural tests of GC evidenced the precipitation of chloride salt and leaching of Portlandite under brine conditions. A higher total porosity of AAC was reported with poorly crystalline calcium carbonate deposits under CO2 saturation. The early strength of one-part AAC should be improved by using suitable additives before their use for oil well-cementing, especially in CO2-rich conditions. (C) 2020 Elsevier Ltd. All rights reserved.