Preliminary formulations of geopolymers for oil well cementing application using metakaolin, fly ash and granulated blast furnace slag combinations

Oil well cementing requires minimum properties in both the fresh and hardened states to ensure adequate casing support. In the context of the cement industry’s decarbonization process, there is growing interest in alternative composites that meet the same technical requirements, with suitable rheological, mechanical, and durability performance. In this study, a binary-based geopolymer containing metakaolin and fly ash, with 10% and 20% replacement by ground granulated blast-furnace slag, was evaluated for application in oil-well cementing. This approach supports sustainable development by using industrial byproducts and reducing reliance on Portland cement, thereby mitigating CO2 emissions. All geopolymer systems exhibited higher viscosity compared to the cement system; however, they retained pumpability. Incorporating slag reduced setting and thickening times, regardless of the predominant precursor. Mixtures with 80% metakaolin/20% slag reached thickening time in 47 min, while 80% fly ash/20% slag achieved a thickening time of 50 min, representing almost 48% less than the cement reference group, which took 105 min. Mechanically, only metakaolin-based systems achieved mechanical strengths between 11.50 and 16 MPa after 24 h, indicating greater practical viability, as they reached the minimum required by API SPEC 10 A at 12 h, with 2.1 MPa and 10.3 MPa, respectively. Fly ash-based systems required longer curing times and achieved lower strengths, failing to meet the required minimum.