致密储层岩体渗流-损伤-断裂机制与压裂模拟研究

The complexity of hydraulic fracturing in tight reservoirs is due to the complex mechanisms of fractured rock damage and fracture induced by water pressure and the interaction between hydraulic fractures and multiscale fractures, which leads the great challenges in fracturing design based on numerical simulation. The purposes of this project are: to understand the mechanisms and features of water flow-fracture propagation-rock damage and failure based on a series of triaxial, fracture failure and permeability experiments. Then summarize the relationship between key variables and propose reasonable assumptions to construct a seepage-damage-fracture model for fractured rock, which is suited for hydraulically fractured analysis; to integrate the upscale finite element method and its basic algorithms into the classical fluid-solid coupling finite element framework with the statistical theory and the constructed constitutive model to build the parallel computing platform to model hydraulic fracture in tight reservoir; to in-depth reveal the laws and the mechanisms of hydraulic fracture propagation based on both laboratory- and field-scale numerical simulations and physical experiments. Expected results of the project can provide some guides for the design and evaluation of hydraulic fracture of tight reservoir.

致密储层压裂复杂性的根源在于水力引起裂隙岩体损伤断裂的复杂机制，以及水力裂缝与不同尺度裂隙的相互作用，并给基于模拟的压裂设计带来极大挑战。项目首先通过开展岩样的三轴实验、断裂破坏试验和渗透性试验，掌握水体流动-裂隙扩展-岩体损伤破坏的机制及特征，总结关键指标量间的关系，并引入合理假设，建立适用于致密储层压裂分析的裂隙岩体渗流-损伤-断裂模型。然后，将升尺度算法纳入到传统流固耦合有限元计算框架，结合统计理论和建立的裂隙岩体本构模型，形成致密储层压裂模拟方法，并并行工具化实现。最后，通过实验室尺度和场尺度的数值模拟与物理试验相结合地揭示水力压裂裂缝扩展规律和机理。项目预期成果可为致密油气储层压裂的设计和效果评价提供参考依据。

致密储层压裂过程涉及复杂的裂隙岩体损伤断裂机制，以及水力裂缝与原生裂隙间的相互作用问题。本项目针对裂隙岩体中的流体流动和固体变形特点，结合多场耦合协同机理，对致密储层在水力作用下的流固耦合及损伤断裂问题进行了深入的研究。项目首先开展了岩样的三轴试验和断裂破坏试验，验证了所提基于全应力应变曲线的岩体脆性指标在不同岩石种类、不同围压条件下的适应性，探究了弹性模量、泊松比和围压等岩石力学参数对岩体脆性的影响。在传统流固耦合有限元计算框架的基础上，引入时间步长积分方法和两种空间离散化稳定策略，提出了全新的无条件稳定的低阶显式多时间尺度有限元公式，建立了适用于致密储层的流固全耦合分析模型，基于连续-非连续方法，结合裂纹任意增量扩展技术，建立了一种基于该方法的流固全耦合模型，并并行工具化实现。最后，为探究储层压裂过程的裂缝扩展规律，分别研究了岩石力学参数和水力压裂工艺参数对水力裂缝起裂和扩展过程的影响。项目所得成果可为致密油气储层压裂的设计和效果评价提供参考依据。