分形裂缝中VES压裂液-颗粒多相流动及多尺度动态耦合机理

VES fracturing fluid is a new high-efficient and clean fracturing fluid. Proppants migration by fracturing fluid in fracturing fracture determines ultimate fracture formation and oil and gas recovery. There is a strong coupling between rheological properties of microscale micelles in VES fracturing fluid and macroscale multiphase flow behavior. The dynamic coupling mechanism is not only the way to accurately describe VES fracturing fluid-particles multiphase flow behavior but also the key to acquire the method to control particles migration. The research employs multiscale method to conduct experimental study on VES fracturing fluid-particles multiphase flow in fractal fracture and dynamic microscale structure of micelles based on visualization method, and elucidate the mechanism of influence of rheological properties of microscale micelles on macroscale flow. Dissipative Particle Dynamics method is employed to simulate rheological properties of fracturing fluid based on finite volume grid. Real-time stress-strain constitutive relations in entire fluid field are obtained and coupled with momentum equation, through which multiscale model and simulation method are built. The relationship between VES fracturing fluid-particles flow pattern and rheological properties of fracturing fluid and fracture characteristics is analyzed. Control methods of flow pattern and rheological properties of fracturing fluid are obtained. The research will not only provide support for predicting fracturing fluid-particles multiphase flow and controlling rheological properties of fracturing fluid but also enrich the research connotations of fluid-particles multiphase flow.

VES压裂液是一种新型高效清洁压裂液，压裂液携颗粒在裂缝中运移效果决定裂缝最终形态和油气采收率。在复杂裂缝形态和强壁面效应下，VES压裂液中微尺度胶束流变特性与宏观多相流动行为强烈耦合，其动态耦合机理既是准确描述VES压裂液-颗粒多相流动的前提，也是寻求控制颗粒运移手段的关键。本项目采用多尺度研究方法，基于可视化方法对分形裂缝中VES压裂液-颗粒多相流动特性以及动态胶束微观结构进行实验研究，阐明微观胶束流变特性对宏观多相流动的影响机理；基于有限体积网格，采用耗散粒子动力学方法模拟流体流变特性，获得实时全场离散应力-应变本构关系，与动量方程耦合，建立多尺度模型及数值模拟方法；分析VES压裂液携颗粒多相流型与流体流变性质、裂缝特征的相关关系，获得流型和压裂液流变性质调控方法。本项目的实施，既可为压裂裂缝中压裂液-颗粒多相流动预测及压裂液流变性质调控提供依据，又有望丰富流体-颗粒多相流研究内涵。

VES压裂液是一种用于油气藏开发的新型高效清洁压裂液，压裂液携支撑剂颗粒在地层压裂裂缝中运移和沉降效果显著影响裂缝最终形态和油气采收率。VES压裂液的复杂流变特性与宏观多相流动行为强烈耦合，其动态耦合机理既是准确描述VES压裂液-颗粒多相流动的前提，也是寻求控制支撑剂颗粒运移手段的关键。本项目采用实验和数值模拟方法研究了VES压裂液-颗粒两相运动特性，获得了VES流体的粘弹性对颗粒在其中沉降和运移特性的影响规律，揭示了VES流体-颗粒两相流动的多尺度耦合机理。首先基于流变学实验和数值模拟开展了VES压裂液的宏观流变性质研究，获得了溶液粘弹性和剪切-拉伸响应特性。采用颗粒尺度直接数值模拟方法，基于宏观粘弹性流体本构模型，获得了流体流变参数对颗粒受力特性的影响规律，建立了粘弹性流体中颗粒曳力的数学模型，在此基础上基于不同的粘弹性流体本构模型，构建了颗粒在粘弹性流体中沉降的数学模型，揭示了流体粘弹性和流道几何约束等条件对颗粒沉降运动状态的影响规律。采用考虑表面活性剂蠕虫状胶束溶液中微尺度胶束断裂和重构的VCM本构模型，获得了胶束的断裂和重构对流动状态以及颗粒曳力的影响规律，揭示了低雷诺数下流体流动及颗粒沉降不稳定产生的原因。同时开展了复杂形态裂缝内压裂液-颗粒两相流动的实验和数值模拟研究，获得了压裂液流变性质对裂缝内流体-颗粒两相流动流型的影响规律。本项目的实施，既可为压裂裂缝中压裂液-颗粒多相流动预测及压裂液流变性质调控提供依据，又有望丰富流体-颗粒多相流研究内涵。