Seyed Hasan Hajiabadi

Silica, a predominant metal oxide and fundamental component of the Earth’s crust, exerts significant influence on diverse geochemical and industrial processes through its interactions with water. This study delves into the surface modification of bentonite clay, as a naturally occurring aluminosilicate source, via treatment with varied concentrations of Al(NO3)3, as a novel surface modification approach, and H2 SO4, as a control technique. The obtained results elucidated important alterations in micro-scale surface characteristics, colloidal stability, and rheological behaviour of the aqueous solutions derived from the modified bentonite samples. Zeta potential analyses showed shifts from a stable colloidal solution in untreated bentonite to heightened instability following aluminium nitrate (and acid) treatment(s). In addition, micro-scale surface analyses employing scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and Fourier-transform infrared (FTIR) revealed significant changes, encompassing heightened degree of coagulation, caused by intensified neutralization, and diminished swelling capacities induced by surface modifications. EDS analysis validated cation exchange processes and intensified agglomeration with Al(NO3)3 treatment. Furthermore, the stability and rheological behaviour of resulting aqueous fluids demonstrated reduced stability in Al(NO3 )-treated samples, comparable to acid-treated samples, indicative of hydrophobic surfaces post-treatment. The findings highlighted the effectiveness of the applied treatment technique, emphasizing practical implications for surface-treated bentonite utilization in different environments. However, observed variations influenced by ion type and concentration prompt the imperative for further research to unveil specific mechanisms of treatment approaches on aluminosilicate systems. This endeavour contributes to advancing comprehension and optimization of silicate performance across diverse applications.

Rock-based geopolymers (GPs) offer a promising alternative to Ordinary Portland Cement (OPC) for wellbore systems due to the scalability, availability, and chemo-physical properties of their precursors. However, their performance in CO2 geosequestration, especially under thermal shocks from injecting cold pressurized CO2 into hot subsurface environments, remains under-explored. This study evaluates the thermal shock response of a granite-based GP designed for CO2 geosequestration. Thermal shocks were induced by rapidly cooling hot GP samples (maintained at 200°C) through immersion in either cold tap water or NaCl brine (5°C). Control samples were immersed in water or brine at room temperature for 2 minutes, followed by 10 hours of drying at room temperature. Macro-scale effects were assessed through measurements of porosity, mass loss, and uniaxial compressive strength (UCS), while microstructural changes were analyzed using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results showed minimal alterations in mass and porosity for water-exposed control samples, with a 5% reduction in compressive strength. Control samples exposed to brine showed increased mass by 11.4%, decreased porosity by 44%, and enhanced compressive strength by 4.7%. Thermal cycling with water-quenching resulted in a 1.4% mass increase, 4.7% porosity decrease, and 26% compressive strength decline. In contrast, thermal cycling with brine quenching led to a 9.3% mass increase, 27.3% porosity reduction, and a 9% compressive strength decrease. Micro-scale analyses of the samples quenched in brine revealed the formation of calcium/sodium/potassium aluminosilicate hydrate (C,N,K)-A-S-H gels, new minerals (particularly zeolites), and NaCl precipitation. In addition, EDS analyses indicated ion diffusion, with Na+ ion penetration being more significant in brine-exposed samples at higher temperatures. Moreover, XRD analyses showed relatively higher crystallinity in NaCl-exposed samples, correlating with improved mechanical properties due to new mineral formations and pore-filling NaCl precipitation. In summary, the study confirms the durability of the granite-based GP system under thermal shocks and brine exposure, attributed to mineralogical alterations and alkali-enriched gel formation, which mitigate the negative effects of thermal stresses and maintain mechanical performance.

Wellbores used in underground production and storage activities, including carbon capture and storage (CCS), are typically sealed using sealants based on Ordinary Portland Cement (OPC). However, leakage along these seals or through them during CCS operations can pose a significant threat to long-term storage integrity. In this review paper, we explore the potential of geopolymer (GP) systems as alternative sealants in wells exposed to CO₂ during CCS. First, we discuss how key parameters control the mechanical properties, permeability, and chemical durability of GPs based on different starting materials as well as their optimum values. These parameters include the chemical and mineralogical composition, particle size, and particle shape of the precursor materials; the composition of the hardener; the chemistry of the full system (particularly the Si/Al, Si/(Na+K), Si/Ca, Si/Mg, and Si/Fe ratios); the water content of the mix; and the conditions under which curing occurs. Next, we review existing knowledge on the use of GPs as wellbore sealants to identify key knowledge gaps and challenges and the research needed to address these challenges. Our review shows the great potential of GPs as alternative wellbore sealant materials in CCS (as well as other applications) due to their high corrosion durability, low matrix permeability, and good mechanical properties. However, important challenges are identified that require further research, such as mix optimization, taking into account curing and exposure conditions and available starting materials; the development of optimalization workflows, along with building larger data sets on how the identified parameters affect GP properties, can streamline this optimization for future applications.