Borate-crosslinked fluids were once restricted from high temperature applications, but advances have improved them for use in temperatures to 300°F. The polymers most often used in these fluids are guar and HPG (Hydroxypropyl Guar). The crosslink obtained by using borate is reversible and is triggered by altering the pH of the fluid system. The reversible characteristic of the crosslink in borate fluids helps them clean up more effectively, resulting in good regained permeability and conductivity. In addition to good cleanup properties, with the proper composition, borate fluids provide good proppant transport, stablefluid rheology, and low fluid loss. The use of borate-crosslinked fluids has increased significantly over the last decade, and HPG-borates show great potential for high permeability applications.
The overall purpose of crosslinking polymers with metals is to increase the viscocity and further improve the rheology of the fluid.