返排液残余稠化剂对循环利用的影响

Effect of Residual Thickener on the Recycling of Flow-back Fluid

为研究瓜尔胶压裂液破胶和循环使用的影响因素,从返排液中残余稠化剂和交联剂性能变化、存在状态以及含量等方面入手,研究残余稠化剂和交联剂对返排液重复配制压裂液性能的影响机理。结果表明,随着破胶时间或破胶剂加量的增加,瓜尔胶压裂液破胶液黏度降低、抽滤时间减少,小分子比例增加;酶破胶具有选择性,破胶后甘露糖与半乳糖的比例保持不变;氧化破胶不具选择性,随破胶时间延长,半乳糖含量下降,分子结构发生变化,侧链半乳糖限制主链甘露糖形成螺旋能力减弱,瓜尔胶水溶性降低,形成絮状沉淀;破胶液中残余稠化剂含量对瓜尔胶溶胀的影响较小,但由于破胶液中长链瓜尔胶分子之间嵌入了小分子交联体,长链间缠绕和交联受到影响,导致压裂液耐剪切能力下降;多次循环破胶液中,小分子比例增加,破胶液黏度大于返排液黏度要求,循环利用返排液时必须控制残余稠化剂糖含量在0.2%以下。

In order to study the influencing factors on the breaking and recycling of guar gum fracturing fluid,the influence mechanism of residual thickener and crosslinking agent on the performance of fracturing fluid prepared by flow-back fluid was studied,from the aspects of performance change,existence state and content of residual thickener and crosslinking agent in flow-back fluid.The results showed that with the increase of breaking time or dosage of breaking agent,the viscosity of guar gum fracturing fluid and the extraction time decreased,and the proportion of small molecules increased.The enzymatic breaking was selective,and the ratio of mannose to galactose remained unchanged after enzymatic breaking.The oxidative breaking was not selective.With the extension of breaking time,the content of galactose decreased,and the molecular structure changed.Galactose side chain limited the helical formation ability of mannose main chain,which led to the decrease of water solubility and the formation of flocculent precipitate.The influence of residual thickener content on the swelling of guar gum was small,but the entangling and crosslinking between long-chain guar gum molecules were affected because of the small molecule crosslinking between long-chain guar gum molecules,which led to the decrease of shear resistance of fracturing fluid.The proportion of small molecules increased in multiple cycles of breaking solution,and the viscosity of breaking solution was greater than that requirement of flow-back solution.The sugar content of residual thickener should be controlled below 0.2%when the flow-back solution was recycled.