三维裂隙岩体水力耦合多尺度分析相场模型研究

In the exploitation of geo-energy such as shale gas development using hydraulic fracturing, the fracture propagtion behaviour of fractured geologcal body under the coupled hydromechanical field is generally recognized as a key question in rock mechanics. The key objective of the proposed ressearch project is to develop and implement a robust, accurate and computationally efficient numerical framework for the modelling and optimization of future Energy Exploitation techniques.In the coarse scale model, a two-level model incoporating multiple discrete (explicit) fracutre surfaces and porous media will be developed to model the crack growth, branching and coalesence behaviour of cracks. The fluid flowing throug the crack surfaces will be modeled by Newtonian fluid. A coupled dual-phase field model accounting for the interaction from fluid and mechanical field. It will be the first phase field model to the applicant's knowledge coupling hydromechanical field for rock mechanics modelling. The advatanges of using phase field model is that the fracture geoemetry is the natural outcome of the simultion without any priori assumptions on crack path continuities, crack geometry and crack kinematics.The hydromechanical prameters such as permeability will be extracted through fine scale model. A semi-concurrent multiscalde modelling approach will be utilized to bridge the coarse and fine scale model through material consitency conditions including pressure gradient, strain tensor and fluid velocity.The measurable deliverable of the proposed project is the new theory, model and code implementation that are capable for effective, accurate and efficient fracture modelling of rock mass subjected to hydromechanical field.

如何有效控制和利用岩体在水力耦合作用下的裂隙扩展行为，是页岩气水力劈裂开采等地下能源开发中面临的核心问题，是我国能源发展中迫切需要解决的关键技术。本项目拟发展、实现和验证三维岩体裂隙扩展水力耦合多尺度分析数值模拟框架；建立显式三维宏观尺度"断裂面-多孔介质"模型，模拟流体通过断裂面之间的流动过程，以及裂隙在流-固相互作用下的扩展、分叉、贯通等力学行为；建立细观尺度水力耦合模型，发展全新的"水力耦合相场"势函数与控制方程。结合相场法（Phase field method）无需单独描述裂纹面几何形态、无需引入断裂模式假定并自然得到材料破坏过程的优势，建立细观裂隙在宏观水力边界条件下的演化分析模型，研究渗透张量等材料参数提取理论与方法；并通过压力梯度、渗流速度等一致性约束条件，建立连接宏细观岩体裂隙扩展的物理准则。本项目将最终形成一套有效、准确和可行的岩体水力裂隙分析计算理论与方法。

如何有效控制和利用岩体在水力耦合作用下的裂隙扩展行为，是能源开发中面临的核心问题，也是我国能源发展中迫切需要解决的关键技术。本项目发展、实现和验证了三维岩体裂隙扩展水力耦合多尺度分析数值模拟框架；建立了显式三维宏观尺度“断裂面-多孔介质”模型，模拟裂隙在流-固相互作用下的扩展、分叉、贯通等力学行为；建立细观尺度水力耦合模型，发展全新的“水力耦合相场”模型计算分析方法。项目完成了：1. 提出水力耦合多尺度问题的非线性破坏计算方法； 2. 基于三维图像扫描，完成了基于砂岩CT图像的岩石的三维细观几何模型及有限元模型。 对试样同时施加单轴或三轴压缩边界条件和稳态渗流边界条件，并全程提取渗透系数和轴向应变在不同时刻的结果。3. 发展了用于模拟复杂裂缝模式的相场三维算法模型，包括裂缝扩展，分叉和接合。相场模型基于应变分解弹性能量，驱动相场的演变。 然后，数值模拟进行缺口半圆弯曲（NSCB）试验和巴西劈裂试验。 随后，研究了具有多个梯形缺陷和二十个平行缺陷的岩石板中的裂缝接合。依托本项目已完成了三维动态水力裂纹扩展相场模型研究，该研究成果国际领先。同时，依托本项目发表了相关SCI论文6篇，公布程序1套，设计完成相似模型压裂实验装置1套。