裂缝在非均匀岩层内扩展机理研究

薄差储层有效开发的关键问题是明确水力裂缝在砂/泥岩界面上的扩展特性. 为了分析裂缝在砂/泥岩界面上的扩展机理, 以ABAQUS 为平台, 利用扩展有限元框架下的分离裂缝模型模拟了裂缝在砂/泥岩界面上的扩展过程, 该模型提出预设虚节点法, 通过在位移的插值函数中引入附加增强项, 实现裂缝扩展独立于网格边界, 获得了裂缝通过砂/泥岩界面的扩展规律. 并采用白光散斑实验对低渗透储层砂/泥岩界面的裂缝扩展进行了实时跟踪, 裂缝扩展过程与数值模拟过程吻合较好, 说明扩展有限元法是定量分析裂缝扩展的有效手段, 同时分析了裂缝穿过界面扩展的影响因素.

THE MECHANISM OF CRACK EXTENSION IN NON-UNIFORM ROCK

A clear understanding of the extension of hydraulic fractures on the sandstone-mudstone boundary is the key issue of effectively developing the thin and poor reservoir. In order to simulate the extension property of the fractures on the sandstone-mudstone boundary, with ABAQUS as a platform, the fracture extension process on the sandstone-mudstone boundary is simulated using the separated fracture model with the extended finite element framework. A preset virtual node method is proposed, to make the fracture extension independent of the grid boundary and the extension evolution on the sandstone-mudstone boundary is obtained through the introduction of additional enhancements in the interpolation function of displacement. The fracture extension on the low permeability reservoir sandstone-mudstone boundary is also tracked in real-time by using the white light speckle experiment. The extension process is in good agreement with the numerical simulation, which indicates that the extended finite element method is an effective means of quantitative analysis for fracture extension, and the fracture extension process on the boundary is also studied.