压裂返排液中残余硼交联剂掩蔽方法

为处理胍胶压裂返排液中存在的残余硼交联剂，达到返排液重复利用的目的，通过考察多元醇和α-羟基羧酸盐对硼酸的络合作用，筛选出了甘露醇、木糖醇、葡萄糖酸钠等3种高效配体，并对比了其掩蔽残余硼交联剂的应用效果。实验结果表明:3种配体与硼酸在常温下均可形成稳定络合物，能有效抑制硼酸水解成硼酸根离子；在络合反应过程中，配体均与硼酸先生成摩尔比为1:1的过渡态络合物，再进一步与游离配体反应生成2:1络合物；随配体/硼酸摩尔比增大，络合效率逐渐提高，当摩尔比不小于2.5时，硼酸能被完全络合；络合物在碱性和高温条件下均具有较高稳定性，不会释放硼酸或硼酸根离子。利用甘露醇和葡萄糖酸钠为掩蔽剂，对返排液中残余硼交联剂进行有效掩蔽后可以直接配制胍胶冻胶压裂液，其耐温耐剪切能力和破胶性能与清水配制压裂液相当，可用于胍胶压裂返排液的重复利用。

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.