酶降解制备小分子瓜尔胶

Preparation of Guar Gum with Low Molecular Weight by Enzymatic Degradation

王世彬 张艺耀 郭建春 王德安 张永春

WANG Shi-Bin ZHANG Yi-Yao GUO Jian-Chun WANG De-An ZHANG Yong-Chun

由于压裂液中的稠化剂以大分子化合物为主，以致压裂液残渣对地层伤害严重，影响到压裂后的增产效果。降低残渣伤害最有效的办法是降低稠化剂的分子量。本文通过酶降解的方法，在较少工艺流程和无溶剂的情况下，控制温度为40~50℃、酶加量3.5 u/mL、降解2 h即可得到满足油田压裂改造需要的较小分子量瓜尔胶。降解后瓜尔胶的重均分子量为4.25×105 g/mol，压裂液黏度为27 mPa·s。瓜尔胶降解前后的红外光谱表明酶降解使瓜尔胶长链分子断裂成较小分子量的链段。小分子瓜尔胶压裂液（3.5 g/L）与有机硼交联剂交联形成的冻胶在100℃、170 s-1下连续剪切2 h后，黏度大于80 mPa·s，抗剪切性较好。该压裂液的残渣为96 mg/L，仅为普通瓜尔胶压裂液残渣的1/4。

Because of the thickeners in fracturing fluids were mainly macromolecular compound, the damage of macromolecular residues to the reservoir seriously impacted well productivity. The most effective way to reduce insoluble residue damage was to decrease the molecular weight of thickener. This paper described a method to get guar gum with low molecular weight (LMG) by enzyme degradation through simple technological process and without solvent. The reaction condition was obtained as follows: 40—50oC reaction temperature, 3.5 u/mL enzyme dosage, 2 hrs reaction time. The weight-average molecular weight of obtained LMG was 4.25×105 g/mol and the viscosity?of fracturing fluid with LMG was 27 mPa·s. The IR spectrum?of guar gum before and after degradation showed that the enzyme had broken the molecular chain which became short chain with low molecular weight. The viscosity of gel which formed by organic boron crosslinker and fracturing fluid including 3.5 g/L LMG was more than 80 mPa·s after shearing 2 hrs at 100oC and 170 s-1. The residue content of LMG fracturing fluid was 96 mg/L, which was a quarter of common guar gum fracturing fluid residue.