With recurrent calls for a reduction in carbon emissions, geothermal (GT) energy has received increasing attention in recent years as a prominent source of clean energy. With current drilling technology, GT wells are being constructed in extremely challenging temperature environments, which could reach more than 600°F (315°C) in situ. However, GT well-cementing technology has not changed much over the past few decades, with ordinary Portland cement (OPC) still being the primary choice of cementing material. OPC has several drawbacks, including brittle behavior, shrinkage upon setting, poor bond strength to formation and casing, susceptibility to an acid gas attack, temperature-induced strength retrogression, and low tolerance toward drilling fluid contamination. These factors could lead to a poor cementing job, thus compromising well integrity and not ensuring proper zonal isolation for the life of the GT well. Thus, there is a need to develop an alternative material that is compatible with the GT environment and able to provide long-term zonal isolation. With a low carbon footprint, self-healing ability, and low shrinkage sensitivity, geopolymers or alkali-activated materials could be a suitable option to augment or even replace OPC. Some of the previous studies on geopolymers have shown that they could be a potential candidate for oil and gas well cementing and civil engineering applications, with some being stable at very high temperatures [up to 1,470°F (800°C)]. Geopolymers are formed by mixing an aluminosilicate source such as fly ash (FA) with an alkali-activating solution, such as sodium or potassium hydroxide or silicate.
The aim of the study reported here is to demonstrate the applicability of geopolymers for GT well cementing. An experimental investigation was carried out to understand the behavior of geopolymer formulations made from FA, metakaolin (MK), and blast furnace slag in a high-temperature environment. The material properties such as porosity, viscosity, thickening/pump time, compressive strength, tensile strength, and bond strength were tested in the laboratory. It was found that geopolymer can be formulated to have the desired rheological properties with adequate pump time and resistance to drilling fluid contamination. In addition, the formulations can exceed the required compressive and tensile strength for GT cementing operations, while obtaining excellent bond strength values. These findings indicate that geopolymers are well-suited to provide long-term zonal isolation in high-temperature GT wells.