Low-density granite-based geopolymer for well cementing: The role of burnt lime in enhancing early strength

Abstract

In the pursuit of sustainable solutions within the oil and gas industry, the environmental and mechanical limitations of Ordinary Portland Cement (OPC) have led to the evaluation of more sustainable alternative materials for oilwell cementing applications. Particularly in shallow-depth cementing operations, where low-density slurries are essential to prevent formation breakdown, current solutions fall short in balancing environmental impact with the industry's performance requirements. Geopolymers, known for their reduced carbon footprint and comparable mechanical properties, have been seen as a promising alternative. However, increasing water content to lower the slurry density remains a challenge for geopolymers due to the weakening effect and prolonged reaction. The specific role of burnt lime (CaO) has the potential to enhance the early strength of low-density geopolymers yet remains under-explored for this particular case. This study aims to fill this gap by examining the effects of two different reactivities of CaO on a low-density granite-based geopolymer at low temperatures and investigate the potential of CaO to enhance the early strength of low-density geopolymers, aiming to provide a sustainable alternative to traditional cementing materials in oil well operation. The investigation consists of viscosity measurements, pumpability tests, and compressive strength evaluations. Additionally, isothermal calorimetry, TGA, XRD, and SEM were conducted to gain a deeper understanding of the behavior of each sample. Supplementary tests were conducted to evaluate the effect of varying CaO concentrations and the impact of mud contamination on the performance of low-density geopolymers. The investigation revealed that calcium oxide did not significantly impact the initial viscosity of the slurry however, it affects gelation and rate of the reaction. Short-term strength was shown to be affected by CaO at two different temperatures, yet negligible effects were seen in the long-term period for geopolymers with a high water-to-solid ratio. The findings suggest that CaO can significantly enhance the early strength of geopolymers, which are crucial properties for cementing operations in oil and gas wells. This could contribute to accelerate the possibility of geopolymers as a viable sustainable replacement for Portland cement especially in shallow and low-temperature well-cementing applications.