矿物对页岩介观裂缝扩展过程的影响及其机理

Shale has extremely low porosity and permeability, that the complex fracture grid must be created through hydraulic fracturing technology to improve the conductivity of shale gas reservoirs. However, the destruction of brittle minerals and the expansion of clay minerals in shale will affect the opening and propagation of natural and artificial fractures. Therefore, it is of great importance to study the influence of minerals on shale fracture propagation for shale reservoir reform. This project intends to conduct Mineral Liberation Analysis (MLA) through shale rock thin sections to obtain the morphology and distribution of each mineral component which includes brittle minerals and clay minerals. The mechanical parameters of each mineral were obtained by Nano-indentation test. Based on the above experimental results, a digital core model is established. Then, according to the properties of discontinuous media and the theory of rock fracture mechanics, the mechanical model of mesoscopic fracture propagation of shale regarding mineral mechanical parameters was established, through regression comparison of the uniaxial and tri-axial mechanical experiments results and computational simulation analysis. Fracture deformation in dynamic mechanics experiment was measured by Digital Image Correlation (DIC) method. Thus, the dynamic influence law of shale minerals on the mesoscopic fracture expansion process is revealed to enrich the basic theory of hydraulic fracturing technology, provide reference basis for fracturing design, and improve the productivity of shale gas.

页岩具有极低的孔隙率和渗透率，必须通过水力压裂技术，创造复杂的裂缝网格，来提高页岩气储层的导流能力。然而，页岩脆性矿物的破坏与粘土矿物的膨胀等，都会影响天然裂缝和人造裂缝的张开与延伸。因此，研究矿物对页岩裂缝扩展的影响规律，对页岩储层改造至关重要。本项目拟通过页岩岩石切片进行矿物解离度分析（MLA），获得各矿物组分（包括脆性矿物与粘土矿物）的形态及分布；通过纳米压痕试验，获得各矿物的力学参数；以上述实验结果为基础，建立数字岩心模型。然后根据非连续介质特性和岩石断裂力学理论，通过回归比对单轴及三轴力学实验与计算模拟分析结果，建立页岩介观裂缝扩展关于矿物力学参数的力学模型。通过数字图像相关（DIC）方法测量动态力学实验中的裂缝形变，从而揭示页岩矿物对其介观裂缝扩展过程的动态影响规律，丰富水力压裂技术的基础理论，为压裂设计提供参考依据，提高页岩气的产能。

页岩矿物的分布及其性质对岩土工程中页岩岩层的力学性质以及页岩气的压裂开采影响巨大。本项目围绕矿物对页岩裂缝开裂和扩展的影响，主要完成了以下三部分内容：通过MLA和纳米压痕试验，在细观空间上将矿物形态和力学性质对应上，分析了陆相页岩矿物的组分、形态分布特点，揭示了不同矿物间共同作用的规律；通过巴西劈裂、预制裂缝圆盘等的力学测试，对矿物填充的天然裂缝进行了开裂规律研究，建立了相应的力学模型，突出了层理对页岩抗拉强度和I型断裂韧度的影响；通过声发射技术监测力学测试试验，对页岩裂缝开裂和扩展的动态规律进行研究，表明具有天然裂缝试样的声发射信号大量产生于裂纹扩展贯通到天然裂缝的交点位置。研究结果对工程中遇到的页岩力学性质劣化分析和页岩气开采中的压裂设计具有一定的参考价值。.在项目执行期间，投稿了高水平学术论文两篇；申请国家发明专利一项，已授权；培养了研究生两名，本科生三名。