基于蛛网仿生模型的纳米材料复合清洁压裂液新方法和机理研究

Due to the low friction, no residues, and low damage to the formation, clean fracturing fluid has attracted a large amount of attentions, especially in the fracturing and production of unconventional oil and gas reservoirs with very low permeability. However, the thermal stability of clean fracturing fluid is generally low. How to increase the thermal stability is always a great challenge. To this issue, based on the cobweb bionic model, this project prepares the functional nanomaterials composite clean fracturing fluids with better thermal stability. The molecular simulation technique is used to design the molecular structure of functional nanomaterials, which can clarify the structure-property law of molecular headgroups and properties of nanomaterials. The functional nanomaterials with low cost and high stability are synthesized through the chemical modified method using silica nanoparticles as the base materials. After mixing with viscoelastic surfactants, the functional nanomaterials composite clean fracturing fluids with high stability can be constructed due to the strong molecular interactions. The synergistic interaction laws between functional nanomaterials and viscoelastic surfactants are illustrated. The cobweb bionic mechanism is clarified. Based on this project, a novel nanomaterial composite clean fracturing fluid suitable to unconventional oil and gas reservoirs can be developed. This can provide the thesis foundation and technical guidance for the effective production of national unconventional oil and gas reservoirs.

清洁压裂液具有摩阻小、无残渣、对地层伤害小等特点备受关注，特别是在渗透率极低的非常规油气藏储层压裂开发中有着巨大的潜力，但目前普遍存在耐温性差的难题。针对这一难题，本项目基于蛛网仿生模型，研制耐温性好的功能纳米材料复合清洁压裂液。利用分子模拟技术设计功能纳米材料分子结构，阐明分子官能基团与功能纳米材料性能之间的构效规律，以纳米二氧化硅为基质材料，借助化学接枝改性方法制备功能纳米材料，通过与黏弹性表面活性剂产生强烈的分子间相互作用力，构筑耐温性能好的纳米材料复合清洁压裂液，揭示功能纳米材料和黏弹性表面活性剂分子间的协同增效作用机理，阐明蛛网仿生机制，形成适用于非常规油气藏的纳米材料复合清洁压裂液新方法，为我国非常规油气藏高效开发提供理论基础和技术指导。

清洁压裂液具有摩阻小、无残渣、对地层伤害小等特点备受关注，特别是在渗透率极低的非常规油气藏储层压裂开发中有着巨大的潜力，但目前普遍存在耐温性差的难题。针对这一难题，本项目创新功能纳米材料作为“链接点”提高清洁压裂液网络结构和耐温性能的理念。首先以廉价易得的SiO2纳米颗粒为基质材料，利用化学改性的方法研制了分散性好、稳定性高的功能纳米材料。基于蛛网仿生模型，合成了长碳链多羟基黏弹性表面活性剂，并以低浓增黏为指标构筑了功能纳米材料复合清洁压裂液体系，并对其压裂液性能、热力学特性和流变特性开展了研究，研究结果显示纳米复合清洁压裂液体系具有易破胶、低残渣、低伤害、耐温耐剪切性好、携砂性强等特点。借助显微粒子测速技术（PIV）和可视化微观孔喉模型，对比研究了牛顿流体、聚合物压裂液和纳米复合清洁压裂液在孔隙介质中的流动特征，研究结果显示，牛顿流体无弹性特征及拉伸作用形变，其流动呈“抛物线型”速度场分布；聚合物压裂液由于长链分子间缠绕产生的结构强度会被拉伸作用诱导产生强汇聚流型；纳米复合清洁压裂液易在拉伸-剪切双重作用下产生破裂-重组的动力学特性，速度场分布会呈现出三种模式，分别是远孔位置处的“抛物线型”、近孔位置处的“马鞍型”及入孔位置处的“U型双峰”汇聚速度场分布。进一步揭示了纳米颗粒复合清洁压裂液的协同增效作用机理和蛛网仿生机制，纳米颗粒表面存在着由表面活性剂分子包覆的双层结构，可与表活剂胶束头部相结合形成桥接点，构建一种新的“蛛网式双重网状结构”，从而进一步提升清洁压裂液的增粘效果及耐温性能。并探究了压裂液破胶液的高效渗吸排油机制，降低界面张力、强化油滴变形和剥离能力提升的同时，纳米颗粒吸附降低了表面粗糙度，减小了流动阻力，多重作用协同增强渗吸排油效果。通过本课题的研究，形成了纳米复合清洁压裂液新方法，为我国非常规油气高效压裂开发提供技术支持，对提高我国石油天然气开采行业的国际竞争力、促进行业科技水平进步具有非常积极的作用。