分子自组装对缔合压裂液黏度“回复”的机理分析

Analyzing the Mechanisms of the “Recovery” of Association Fracturing Fluids Viscosity by Molecules Self-assembly

近些年,通过疏水缔合聚合物与表面活性剂复配所形成的具有"超分子结构"的缔合体系,被作为新型清洁压裂液已有相关的报道。绝大多数文章关注稠化剂的研发和性能评价,对这种缔合压裂液体系的成网机理、剪切"回复性"机理等基础研究较少。通过变剪切流变实验、环境扫描电镜、支撑剂悬浮实验,对缔合压裂液体系的成网机理、剪切"回复性"机理进行了分析研究,从可视化的角度直观地分析并阐述了分子自组装对缔合压裂液体系表观黏度"回复"的作用。分析研究结果表明,缔合压裂液的"空间网络状结构"是通过疏水支链与表面活性剂"共用"胶束、疏水缔合聚合物分子间缔合和分子间缠绕的方式形成的;剪切作用撤销以后,拆散了的表面活性剂自组装成新的"胶束"并与剪碎了的疏水缔合聚合物的疏水支链,重新自组装形成新"网络状结构";分子层间的"滑移"作用,使缔合压裂液体系新"网络状结构"处于一种"动态平衡"状态,并以新构建的"网络状结构"悬浮支撑剂。

In recent years, reports have been found of new clear fracturing fuids, a liquid system with “supramolecular structure” formulated with hydrophobically associating polymers and surfactants. Most of the reports have focused on the development and performance evaluation of the polymeric thickeners, while the mechanisms of forming molecular network and regaining viscosity through shearing of the fracturing fuids have rarely been studied. To study the mechanisms mentioned above, varied shearing rheology experiment, environmental scanning electron microscope （ESEM） experiment and proppant suspending experiment have been conducted, and the effects of molecules’ self-assembly on the two mechanisms have been visually analyzed and explained. The analytical results demonstrated that the “spatial networking structure” of the association fracturing fuid is formed through the “shared” micelles between hydrophobic molecular side-chains and surfactant molecules, inter-molecular association and inter-molecular entanglement of the hydrophobically associating polymer. When shearing of the fracturing fuid is stopped, the shear-broken surfactant molecules will form new “micelles” through self-assembly, and further re-form new “networking structure” with the hydrophobic side-chains of the shear-broken hydrophobically associating polymer. “Sliding movement” between two layers of molecules causes the new “networking structure” of the “association fracturing fuid” to be in a “dynamic equilibrium” state, and to suspend proppants with much tighter “networking structure”.