动荷载下页岩裂隙多尺度演化试验与理论研究

More attentions are paid on the multi scale evolution of shale fractures, its simulation method and the engineering application of the shale in this project, the load including different loading rates. The compression failure experiment of fractured shale specimen is carried out by using the MTS equipment, the impact tests are carried out by using the multi-function SHPB system, and the hydraulic fracturing tests are carried out by using the three axis model test system. The fracture’s initiation, length and propagation is monitored by using the ultra-high speed photography, the scanning electron microscope (SEM) and X-ray computed tomography machine (CT). With the help of the 3D digital image correlation method, the fracture network’s evolution is analyzed and the loading rate dependence characteristics is studied. Furthermore, by comprehensive application of the reconstruction of the rock with fracture network, the numerical rock sample with fractures is built, and the fractures multiscale evolution is simulated by the numeral manifold method and the meshless method. Finally, the relation between the fracture network’s evolution and the differential stress field and the loading rate is analyzed. The increase production method and the optimized fracturing design measures of the production wells is presented. The objective of this project will provide the theoretical explain of the shale fractures’ evolution and numerical simulation technique, which is very valuable in the production of the shale gas and the coalbed methane mining engineering.

本项目紧密围绕页岩不同应变率动载条件下裂隙多尺度演化和数值仿真方法开展深入细致的研究。通过开展裂隙页岩试样压缩破坏实验、冲击实验和水力压裂模拟试验，综合运用X射线CT扫描技术、扫描电镜（SEM）、高速摄影仪和三维数字图像相关技术（3D-DIC），观测裂隙扩展、演化和和裂隙网络生成规律，分析裂隙断裂参量的率相关性；在此基础上，应用裂隙三维重构技术、多尺度模型整合和数值流形与无网格法相结合方法，开发页岩水力压裂的多尺度计算与仿真技术，分析局部应力场变化和加载率对裂隙网络形成及渗透的影响规律，获得水力压裂页岩的水力性质，进而结合页岩气开发工程，提出水力压裂井的增产优化设计思路和方法。项目研究成果有助于岩石力学与非常规能源开发学科的发展，对于页岩气、煤层气开发和增产措施研究均具有重要意义。

项目通过室内试验、现场试验、理论模型研究以及数值仿真等研究手段，重点研究动荷载下岩石裂纹扩展、裂隙演化规律及其数值仿真方法与技术。项目综合运用霍普金森压杆试验系统、扫描电镜、高速摄影仪和3D-DIC技术，开展了类岩石材料预制裂隙试样、裂隙煤岩、预制裂纹页岩的单轴压缩、巴西劈裂、冲击加载、循环加载等试验与分析，获得了裂纹起裂、演化规律和与加载速率的相关性，并获得裂纹分布和扩展对试样强度、破坏模式的影响规律；根据页岩室内试验研究成果，建立了综合考虑化学势变形、流体与应力耦合的本构关系；为解决模拟复杂断裂网络生成过程中效率低、收敛性差的问题，提出了一种基于全耦合扩展有限元的快速模拟方法；通过采用颗粒流开展含层理试样的三维压缩破坏仿真，得到了含层理试样破坏过程裂纹的起裂、扩展和演化规律。研究成果成功应用于某高速公路隧道工程及油气井井壁稳定性分析。