No abstract

Geopolymer material has a potential to function alongside Portland Cement as an efficient cementitious material for well cementing and plug & abandonment applications. Geopolymer material requires retarding agents to be displaced into the well while considering the properties required to maintain efficient zonal isolation through superior mechanical properties. Chemical admixtures affect the material structure and can, in some cases, jeopardize material integrity if not engineered properly to suite downhole conditions. The present article shows the effect of Zn2+ and K+ species have as retarding agents on slurry, mechanical, and microstructural properties. The approach has been carried out to obtain a preliminary overview of how retarding agents can behave in mix design slurries where eventually sealing performance was examined. Samples were cured and examined for periods of 1, 3, 7, 14, and 28 days at downhole conditions. The results obtained confirm a retardation effect by the addition of Zn2+ and K+ species and some shortcomings in early strength development due to a poisoning mechanism by Zn2+ species. This phenomenon indicates the formation of Ca-Zn phase that can hinder the nucleation of the geopolymeric gel structure. No significant effects were observed on the microstructural development throughout the curing period. The effect of Zn2+ species was also observed in increasing threshold for hydraulic sealability. It may be concluded that the tested retarding agents require furthermore development to minimize shortcomings in mechanical properties specifically early strength development.

In this paper, the impact of temperature and admixture-based salts on the mechanical and rheological properties, and composition of geopolymers was studied. Neat geopolymer and Class-G cement, manufactured by Dyckerhoff, were used as reference samples at elevated temperatures. To enhance the additive properties of the geopolymer slurry, a combination of K and Zn was examined with a variety of K:Zn ratio ranging from ∼0.15 to ∼0.25. The workability of samples was tested by using an atmospheric consistometer, while other rheological properties were examined by running fluid loss test, and rotational viscometer test. The sample with the best workability was cured for 1, 3, and 7 days at bottomhole static temperatures of 70 and 80°C and pressure of 140 MPa where the mechanical properties were examined by ultrasonic cement analyzer and uniaxial compressive strength test. X-ray diffraction was used to analyze the composition of samples at different curing times and temperatures. The obtained results showed that the salt derivative admixtures have a significant impact on the oligomerization and polycondensation phases, where it distinctively elongated the setting time, enhanced strength, and strength development. On the other hand, the temperature effect was clearly observed by reducing rheological properties, while maintaining similar mechanical properties.

Geopolymers are the most promising alternative to Ordinary Portland Cement for oil-well cementing and well abandonment. To that end, the slurry needs a required pumping time ensured by the addition of retarders. Although zinc has been widely known to prolong the setting time of geopolymers, its mechanism of action has yet to be fully elucidated. It is herein hypothesized that zinc ions impede the first stages of silicate oligomerization (Si–O–Al), culminating in longer setting times. Pumping time measurements showed that Zn(NO3)2 delayed the setting time by 5 h in comparison to the zinc-less sample. DFT calculations revealed Si(OH)4 to react with [Zn(OH)4]2− via a barrierless transition state, evidencing a kinetic ground for the retardation effect. Additionally, Raman spectroscopy corroborated the DFT results by showing that Q3 species in the proposed mechanism are formed more rapidly in the presence of zinc ions than in its absence.

Examination of alternative cementitious material cured under elevated temperatures is essential to qualify their applicability in field operations. Geopolymers rise as an alternative for Ordinary Portland Cement in oil and gas applications due to its lower carbon footprint and raw material availability. Using chemical admixtures is crucial to engineer geopolymer material for displacement and to maintain well integrity and zonal isolation under elevated temperature and pressure. In this study, the rheological and mechanical properties of rock-based geopolymers, developed for utilization at elevated temperatures, have been examined with the addition of chemical admixtures to test their performance under operational conditions. Neat Class-G cement, by Dyckerhoff, was used as a reference sample for comparison at elevated conditions. The effect of Zn2+, K+, Na+ and Ca2+ species was examined on geopolymer properties. Samples were cured for 1,3, and 7 days at bottomhole static conditions. Properties examined in this study include workability, fluid loss, and viscosity for slurry properties. On the other hand, sonic strength, uniaxial compressive strength, and tensile strength were examined throughout the curing periods. The obtained results exhibited an enhancement in overall properties with an increase in workability and overall strength of the material while considering the poisoning effects from the usage of Zn2+ species. It was concluded that the combination of Na+ and Ca2+compensated the poisoning effect foreseen by the addition of Zn2+ species in geopolymer systems.