基于气泡尺度的携砂VES-CO2泡沫液在裂缝中的多相流动与颗粒运移机制

Hydraulic fracturing is one of highly efficient development technologies for low permeability reservoir. It has an important strategic significance for improving oil and gas production and ensuring energy security. The development of foam fracturing fluid is an important achievement of fracturing technology. However, because of the diversity of foam structure, the study of traditional sand-carrying fracturing fluid flowing in the fracture mainly focuses on the macroscopic settling properties of particles, and the obtained conclusions related to the evolution properties of macroscopic foam rheology and particle settling velocity are widely different. Consequently, it is difficult to guide the field application of foam fracturing. Therefore, the project, as for clean and efficient VES-CO2 foam fracturing fluid, will reveal mechanism of multiphase flow and particle migration of sand-carrying VES-CO2 foam fracturing fluid, based on the multi-dimensional and multi-scale spatial structure of this sand-carrying foam in the fracture. First of all, the spatial structure which is composed of particles and VES-CO2 foam of different values of foam quality and bubble size is investigated. Then the multiphase physical model that shows the “wet foam fluid and solid particles” is established on the bubble scale. Secondly, the interaction between bubble and particle phases in the flowing sand-carrying foam is explored. Dynamic influences of this interaction between phases, the fracture wall and its size on local foam structure and mechanical parameters are comprehensively investigated, and then the influence mechanisms of these factors on particle sedimentation and migration are revealed. This topic will further enrich theoretical system of the multiphase fluid dynamics. It also provides theoretical foundation for design and effect analysis of VES-CO2 foam fracturing in the development of low permeability reservoir.

水力压裂是低渗油气藏高效开发技术之一，对提高我国油气产量，保证能源安全具有重要战略意义。泡沫压裂液的发展是压裂技术的一项重要成就，但由于泡沫结构的多样性并且传统携砂液在裂缝中流动的研究以宏观颗粒沉降特性为主，所得宏观泡沫流变和颗粒沉降速度演变特性的结论迥异，难以指导泡沫压裂现场应用。为此，本项目针对清洁高效的VES-CO2泡沫压裂液，拟立足于裂缝中携砂泡沫的多维多尺度空间结构，揭示其多相流动与颗粒运移机制。首先研究颗粒与不同泡沫质量和气泡尺寸的VES-CO2泡沫组成的空间结构，建立基于气泡尺度的“湿泡沫流体+固体颗粒”的多相物理模型；其次探究流动的携砂泡沫中气泡相与颗粒相之间的交互作用，综合考察相间作用、裂缝壁面和尺寸对局部泡沫结构和力学参数的动态影响，揭示这些因素对颗粒沉降与运移的影响机理。本课题将进一步丰富多相流体动力学的理论体系，也为VES-CO2泡沫压裂设计及压后分析提供理论依据。

水力压裂是低渗油气藏高效开发技术之一，对提高油气产量，保证能源安全具有重要战略意义。泡沫压裂液的发展是压裂技术的一项重要成就，但由于泡沫结构的多样性并且传统携砂液在裂缝中流动的研究以宏观颗粒沉降特性为主，所得宏观泡沫流变和颗粒沉降速度演变特性的结论迥异，难以有效指导泡沫压裂现场应用。本课题针对清洁、高效的VES-CO2泡沫压裂液，采用实验和数值模拟研究结合，首先搭建了矩形裂缝中泡沫流动实验平台，研究了不同宽度的裂缝中VES-CO2泡沫压裂液的结构特性、多相流动与动态的支撑剂沉降特性，发现携砂泡沫的临界沉降流速随支撑剂比例的增加呈现先减小后增大，并且在泡沫质量为0.75-0.8，泡沫流体的动态携砂性能最强，并获得了多因素影响的携砂泡沫流体的临界沉降流速表达式；其次，基于实验观察，采用Surface Evolver数值模拟方法构建了不同接触角和不同泡沫质量下可变形的准平衡泡沫模型，获得了裂缝中二维泡沫的结构及剪切流变特性，发现泡沫结构的平均配位数随液体份额的增加可分为3个不同区域，展现了配位数线性变化区的斜率与薄膜接触角之间的线性关系，并且发现泡沫屈服应力与泡沫质量呈幂律关系，与薄膜之间的接触角的余弦值呈线性关系；第三，采用Surface Evolver数值模拟方法建立了“湿泡沫流体+固体颗粒”的数值计算模型，多尺度阐明了裂缝中流动泡沫相与颗粒相之间的动态结构演变与沉降受力之间的关系，揭示了泡沫压强变化是引起泡沫中多颗粒沉降时呈现的加速和受阻现象的内在本质原因。最后，分别基于静态泡沫表面能最小和变形泡沫薄膜的受力平衡理论，采用Surface Evolver数值模拟方法和Morse-Witten理论构建了三维干泡沫和湿泡沫数值模型。以上研究结果丰富了多相泡沫物理学的内容，为VES-CO2泡沫压裂设计及压后分析提供理论依据，也可为三维泡沫流动、泡沫能源材料开发等提供重要的模型参考。