A masking method used for the boron crosslinker remained in the back flow of fracturing fluid

In order to treat the boron crosslinker remained in the back flow of guar fracturing fluid so as to recycle the back flow, the complexation of polyalcohol and α-hydroxyl carboxylate on boric acid was investigated, and three efficient ligands were screened out, including mannitol, xylitol and sodium gluconate. Then, their masking effects on residual boron crosslinker were experimentally compared. It is indicated that stable complex can be generated from boric acid and each of three ligands to inhibit effectively the boric acid from hydrolyzing into borate ion. In the process of complexing reaction, transition complex with mole ratio of 1:1 is firstly generated from the ligand and the boric acid, and then the complex of 2:1 is generated after the further reaction with the free ligand. The complexing efficiency increases gradually with the increase of ligand/boric acid mole ratio. When the mole ratio is higher or equal to 2.5, the boric acid is chelated completely. In alkaline environment or high temperature, the complex is stable and no boric acid or borate ion is released. When mannitol or sodium gluconate is used as the masking agent, the guar fracturing fluid can be prepared directly after the boron crosslinker remained in the back flow is masked effectively, and its temperature resistance, shear resistance and gel breaking performance are as good as those of the fracturing fluid prepared from clean water. This method can be used for the recycling of back flow of guar fracturing fluid.