Influence of zirconium crosslinker chemical structure and polymer choice on the performance of crosslinked fracturing fluids

Commonly used borate crosslinkers produce weak fracturing fluids at high temperature, high pressure, high salinity, and low pH conditions. Accordingly, zirconium crosslinkers were developed to address these shortcomings. Zirconium crosslinking chemistry is complicated and depends on many factors such as pH, ionic strength, ligand type, ligand order, and ligand to metal ratio. This work evaluated the rheological performance of four commercial zirconium crosslinkers with a polysaccharide and a polyacrylamide. The tested crosslinkers are manufactured with similar zirconium content but differ in ligand type and ligand order, producing different crosslinker chemical structures. The rheological performance was assessed using an HPHT rheometer at 93-204 degrees C for 1.5 h. Shear tolerance performance was evaluated under shear rates of 40 s(-1)-1000 s(-1). The results showed substantial variation in crosslinking performance due to the differences in the crosslinker chemical structure and type of polymer used. Zirconium lactate and propylene glycol crosslinker exhibited the greatest enhancement in shear and thermal stability with the polysaccharide-based fracturing fluid. Remarkably, the same crosslinker performed the least with the polyacrylamide-based fracturing fluid. However, Zirconium triethanolamine and lactate demonstrated considerable improvements in shear and thermal stability with the polyacrylamide-based system. The work unravelled the influence of the zirconium crosslinker ligand type and ligand order on the rheological properties of both tested polymers. The performance evaluation showed that shear resistance, crosslinking delay, and thermal stability could be improved by utilizing the appropriate crosslinkers. The enhancements ultimately reduce additional additives required, prevent screenouts, and save cost during field treatments.