Evaluation of Class F fly ash-based alkali-activated materials for Civil and Petroleum Engineering applications

Advancements in technology have allowed oil, gas and geothermal well construction in into progressively more challenging subsurface environments, with deeper depths, higher temperatures and pressures, etc. With this progress arises the need for well cementing solutions that can perform better than ordinary portland cement (OPC), with an ability to better handle high pressure / high temperature (HPHT) conditions while possessing a more tolerant chemical composition to drilling mud contamination. Faulty cement jobs due to poor performance of OPC have allowed for the occurrence of micro annuli, putting many wells at risk of a well integrity failure. Such a failure compromises zonal isolation, which can in turn lead to high costs for repair that have not typically been factored into operating budgets. Likewise, civil infrastructure durability has become a key concern for much of the United States due to aging structures and the deterioration of OPC concrete with time. While performance concerns pose a significant risk, the CO₂ emissions associated with OPC production are also at the forefront of concerns about climate change. The topic of this report is alkali-activated materials (AAM) or geopolymers, produced from fly ash, which are currently investigated for use as OPC alternatives. They are of interest because suitable strengths and rheological behaviors have been observed when these materials are subjected to elevated temperatures or mud contamination. To understand the effects of various activators and fly ash compositions on geopolymer formulations, a variety of tests have been conducted at different temperature and pressure conditions. These tests include measurements of rheological behavior, set time, unconfined compressive strength (UCS), tensile strength, and bond strength. As a result of this testing, it has been shown that geopolymers exhibit desirable rheological profiles and set times for a variety of different applications. Their compressive strength was also shown to be equivalent to - or greater than - OPC for most formulations. Furthermore, their tensile strengths and bond strength profiles were often found to be better than OPC. Ultimately, with this research, geopolymers are shown to be viable and appropriate alternatives to OPC for both the oil, gas and geothermal well construction as well as the civil infrastructure industry. An added benefit of geopolymers is that the base material is a waste material, with no further release of CO₂ in manufacturing. Thus, there is the opportunity to utilize a new material for cementation purposes that outperforms OPC while decreasing environmental impacts.