Improved understanding ultra-high strength gel for sealing operations: gelation kinetics and mechanism

Polymer gel has been accepted as a useful tool for solving many sealing operations such as fluid loss control, enhanced oil recovery, water and gas shutoff, wellbore integrity, and well stimulation in the upstream of petroleum industry. In a previous study, we used acrylamide (AM), N,N'-Methylenebisacrylamide (MBA), xanthan (XC) and chromium acetate (Cr3+) to obtain ultra-high strength gel (USGel). Some interesting phenomena, such as the more than 10 times increase in gel strength by 0.05% Cr3+ and the counter-conventional decrease in gel strength by inorganic particles such as layered silicate materials (LSM), silicon dioxide nanoparticles (SiO2) and laponite (RDS), have not been well explained. In this paper, the gelation kinetics and mechanism of USGel were investigated mainly by bottle, DSC, infrared spectroscopy, and environmental scanning electron microscopy (ESEM) experiments, which explained that Cr3+ significantly increased the gel strength of USGel, while inorganic particles had a negative effect on the gel strength. The experimental results showed that Cr3+ preferentially cross-linked AM and XC than MBA, and the gelation rates of Cr3+-XC and Cr3+-AM were 107% and 92.9% faster than AM-MBA, respectively. It is speculated that the triple network structure and physical entanglement formed by AM-MBA, XC-Cr3+, and AM-Cr3+ are the main reasons for significant improvement of gel strength by Cr3+, and the cross-linking competition between LSM and Cr3+ and reduction of entanglement number are the main reasons for the significant reduction of gel strength by LSM. This paper provides new insights into the preparation of ultra-high strength gels and the usage of inorganic particles.