Borate crosslinkers are the most commonly used crosslinker in fracturing fluids. However, they exhibit lower performance at high temperature, high pressure, high water salinity, and low pH applications. Consequently, zirconium crosslinkers are utilized to address these limitations. Zirconium crosslinking chemistry is complex and depends on many factors such as pH, metal to ligand ratio, ligand order, ionic strength, and type of polymer used, which in turn influence the delay time, thermal stability and shear resistance performance.
This work evaluates the rheological performance of four different zirconium crosslinkers with a biopolymer and a synthetic polymer. The tested crosslinkers are manufactured in different chemical structures. The two polymers tested are 40 lb/1,000 gal CMHPG and 40 lb/1,000 gal synthetic polymer. The rheological performance was measured through HPHT rheometer (100 s−1 shear rate) at 200-400°F for 2 hours. The shear tolerance performance was also evaluated under a custom shear rate schedule (100-1000 s−1).
The results show significant variation in crosslinking performance due to the changes in crosslinker chemical structure and type of polymer used. Zirconium lactate and propylene glycol crosslinker shows the highest enhancement in shear and thermal stability with CMHPG based fracturing fluids. Surprisingly, the same crosslinker performed the least with synthetic polymer-based fracturing fluids. However, Zirconium triethanol amine and lactate showed significant enhancements in shear and thermal stability with synthetic polymer-based systems. The results also show and discuss the influence of systematically changing crosslinker ligand order in CMHPG and synthetic polymer-based fracturing fluids.
The work studies the influence of the zirconium crosslinker chemical structure on the rheological properties of both biopolymer and synthetic polymer-based fracturing fluids. The performance evaluation shows that delay time, shear and thermal stability can be enhanced by manufacturing the appropriate crosslinker chemical structure, thus reducing additional additives required used and saving cost.