Multifunctional Boronic Acid Crosslinker for Fracturing Fluids

摘要

Boron-crosslinked guar-based fluids are widely used in hydraulic fracturing applications and, unlike metal-crosslinked fluids, they are tolerant of high-shear conditions and often result in superior fracture conductivity because of better post-fracture cleanup. Guar is a natural polymer that contains insoluble residues, which can cause fracture conductivity damage. To help minimize this damage, lower-concentration polymer crosslinked fluids have been developed (18 to 20 lbm/1, 000 gal). This approach is limited to polymer loadings above the polymer critical overlap concentration (C*). Below this concentration, unstable crosslinked gels are likely. The development of a new technology that permits the use of crosslinked guar at concentrations near or below C*is presented in this paper, as well as initial results obtained from field testing. Well-behaved crosslinked fracturing fluids have been formulated at guar concentrations at 8 to 10 lbm/1, 000 gal with this technology. This new technology is based on the use of a water-soluble long chain polymer that includes boronic acid moieties, which can crosslink guar polymer below C*concentration. The chemistry of this polymeric crosslinker and the resulting gels are similar to that of conventional borate crosslinkers. Synthesis and optimization of the polymeric boronic acid crosslinker is presented, along with rheology and conductivity studies. This new technology provides the fracture design engineer with a new crosslinked fluid system that can reduce the potential for conductivity loss resulting from fracturing fluid damage by reducing the amount of guar gum (and insoluble residue) required to fracture a well by half or more.