压裂返排液中瓜胶浓度检测及分子结构解析

压裂返排液中的主要成分是瓜胶，其有效含量的确定以及分子结构的变化对于返排液后续的处理具有指导作用。利用瓜胶的化学性质建立了采用蒽酮比色法检测返排液中瓜胶浓度的方法，建立的标准曲线线性相关性为0.999 2，回收率在96.5%～101.1%之间，方法重现性高，准确可靠。同时利用凝胶色谱（GPC）与飞行时间质谱联用的技术（LC/Q-TOF-MS）解析了压裂返排液中瓜胶的分子量和分子结构的变化过程。结果表明，凝胶色谱测量瓜胶分子量的标准曲线线性相关性为0.995 5，玛湖地区使用的瓜胶的相对分子质量约为84万，随返排时间的增加返排液中大分子瓜胶显著减少，加入氧化破胶剂后瓜胶的B-O键优先断裂，瓜胶生成聚二醇络合物。 

Concentration Detection and Molecular Structure Identifcation of Guar Gum in Fracturing Flowback Fluids

The main component in fracturing flowback fluids is guar gum, the detection of its effective content and the change of its molecular structure are of importance in subsequent treatment of the flowback fluids. Based on the chemical properties of guar gum, anthrone colorimetry has been selected for use in detecting the concentration of guar gum in fracturing flowback fluids. The linear correlation coeffcient of the standard curve established is 0.999 2, and the percent recovery is between 96.5% and 101.1%. This method has a high repeatability and is accurate and reliable. Using GPC and LC/Q-TOF-MS method, the changing of the molecular weight and molecular structure of the guar gum in the fracturing flowback fluid was identifed. It was found that the standard curve linear correlation coeffcient of using GPC to measure the molecular weight of guar gum was 0.995 5. The relative molecular weight of the guar gum used in Mahu area was about 840,000, and the content of the high molecular weight guar gum in the flowback fluids was decreasing obviously with time. The B-O bond in the molecules of guar gum can be broken preferentially by adding oxidizing gel breaker, and the guar gum is then turned into PEG complex.