水力压裂支撑剂运输与裂纹扩展的数值研究

Hydraulic fracturing is a major and successful technology in industrial exploration of shale gas. In the operation, solid proppant particles flow with fracturing fluids into fractures, playing an important role in preventing crack closure and maintaining the conductivity of fracture network. The supporting performance of the proppants in the fracture network has a significant impact on shale gas productivity. This proposed project is aimed to establish a coupled particle-fluid-solid numerical model, which can be utilized to computationally analyze the transport mechanism of proppants in the fracturing fluids and their interaction with fracture propagation. In the developed model, the Discrete Element Method (DEM), Computational Fluid Dynamics (CFD), and Extended Finite Element Method (XFEM) are used to simulate the motion of proppants, flow of fracturing liquids, and propagation of rock fractures, respectively. The three numerical schemes DEM/CFD/XFEM are coupled to model the interaction of proppants, fracturing liquids, and rocks. The results obtained from this project will reveal the effects of proppant properties, fracturing liquid properties, and crack size on the transport of proppants, and establish a fracture model considering the interaction between proppant-liquid two-phase flow and rock fracturing behavior. Therefore, the selection and transport control of the proppants can be theoretically guided for the optimization of proppant supporting performance and the improvement of efficiency of shale gas exploration.

水力压裂是开采页岩气的重要技术手段，操作中固体支撑剂颗粒随压裂液进入裂纹，起到阻止裂纹闭合、保持缝网导流性的重要作用。支撑剂对整个缝网的支撑效果将直接影响页岩气产量。本项目旨在建立颗粒-流体-固体耦合问题的计算模型，通过数值模拟分析支撑剂在压裂液中的运输机制，以及支撑剂-压裂液两相流动与岩石断裂行为的耦合影响。在所发展的计算模型中，离散单元法（DEM）、计算流体动力学（CFD）和扩展有限单元法（XFEM）分别用来模拟支撑剂颗粒的运动、压裂液的流动和岩石裂纹的扩展；颗粒、压裂液和岩石之间的相互作用通过以上三种数值方法的耦合来实现。本项目的研究结果将揭示支撑剂颗粒属性、压裂液性质、裂纹尺寸等因素对支撑剂流动特性的影响规律，建立考虑支撑剂-压裂液两相流动与岩石断裂耦合作用的断裂力学模型，为支撑剂的选取和运输行为控制提供理论指导，以实现最优支撑效果，提高页岩气开采效率。

水力压裂是开采页岩气的重要技术手段，固体支撑剂颗粒随压裂液进入裂纹，起到阻止裂纹闭合、保持缝网导流性的重要作用。本项目基于耦合的离散单元法（DEM）、计算流体（CFD）和浸没边界（IBM）方法，建立了颗粒-流体-固体耦合的数值模型，实现了对支撑剂-压裂液在裂纹中两相流动的数值模拟。在所发展的计算模型中，DEM、CFD和IBM分别用于模拟颗粒、流体和固体边界。利用发展的数值方法和计算程序，研究了颗粒-流体的两相流动过程，揭示了支撑剂在裂纹中的输运机制，系统阐释了颗粒材料性质与流动速度对支撑剂输运特性的影响规律，为水力压裂中选择合适的支撑剂颗粒提供了一定的依据。在球形颗粒的基础上，进一步模拟了柔性纤维颗粒，及其热传导过程，为研究包含复杂支撑剂和多物理现象的水力压裂过程提供了一个有效工具。