Fly ash Class C based geopolymer for oil well cementing

Abstract

For many years Portland cement has been used in oil well cementing. Even though Portland cement has been used for many years, it has several drawbacks, including operational failures and severe environmental impacts. Fly ash based geopolymer cement has been recently investigated as a low-cost, environmentally friendly alternative to Portland cement. This research develops a novel formulation of Class C fly ash based geopolymer and investigates its applicability as an alternative to Portland cement in hydrocarbon well cementing. Twenty-four variations of fly ash Class C based geopolymers were prepared, and by comparing several of their properties using API standard tests, the most favorable geopolymer formulation was determined. The effect of varying the ratios of alkaline activator to fly ash, sodium silicate to sodium hydroxide, and sodium hydroxide concentration was investigated. The selection of the formulation was based on four different tests, including rheology, density, compressive strength, and fluid loss test. Then, a comparison between the selected mix design and Portland cement was conducted using the same tests, in addition to stability tests (sedimentation test and free fluid test). Based on our results, geopolymer was found to have superior rheological and mechanical properties compared to the Portland cement. The geopolymer design, which had lower fluid loss, 93 ml after 30 min, sufficient compressive strength, 1195 psi in 24 h, and an acceptable density, 14.7 lb/gal, and viscosity, 50 cp, was further compared to the Portland cement. The higher mechanical strength of geopolymer using fly ash Class C compared to Portland cement is very promising for achieving long-term wellbore integrity goals and meeting regulatory criteria for zonal isolation.