Fully 3D Simulation of Hydraulic Fracture Propagation in Naturally Fractured Reservoirs Using Displacement Discontinuity Method
Fully 3D Simulation of Hydraulic Fracture Propagation in Naturally Fractured Reservoirs Using Displacement Discontinuity Method
复制标题
使用位移不连续法对天然裂缝性油藏中水力裂缝扩展进行全 3D 模拟
DOI：
10.2118/209219-pa
复制
发表时间：
2022
期刊：
影响因子：
3.6
通讯作者：
Hangyu Li
中科院分区：
文献类型：
--
作者：
Huiying Tang;Haipeng Liang;Liehui Zhang;Hangyu Li
总结
天然裂缝的形状、尺寸和方向显著影响非常规储层（例如页岩气/油、致密气和增强地热系统）中水力裂缝的几何形状。在平面应变假设下，通过大量的数值模拟和实验分析，将水力裂缝与天然裂缝相遇后的行为概括为穿越、转向、跨越和停止。然而，在实际情况下，天然裂缝和水力裂缝的几何形状比2D模型假设的垂直和矩形形状复杂得多。对天然裂缝高度和倾角作用的实验研究揭示了一些其他现象（如，流体驱动的水力裂缝沿着天然裂缝的后侧向上传播的旁路过程），这不能在2D中被捕获。为了更好地描述不同类型裂缝之间的相交行为，在我们以前只考虑水力裂缝扩展的模型的基础上，建立了一个基于位移不连续方法（DDM）的全三维模型。提出了一种新的判断水力裂缝是否会在三维空间中穿越胶结天然裂缝的穿越判据。采用连续节点捕捉法对水力裂缝面与天然裂缝面之间的演化曲线进行协调网格的构造，只改变一小部分节点的位置，而不改变节点的连通性。利用该模型，研究了水力裂缝与不同韧性、大小、方向和数量的天然裂缝相交后裂缝几何形状的演化。由于考虑了一个额外的维度，允许裂缝在更多的方向上扩展，导致一系列复杂的裂缝几何形状。本文提出的动态网格演化方法可以促进DDM在全三维裂缝网络模拟中的发展。
Summary
The shape, size, and orientation of natural fractures significantly impact the geometry of hydraulic fractures in unconventional reservoirs, such as shale gas/oil, tight gas, and enhanced geothermal system. The behaviors after the hydraulic fracture encounters natural fractures have been summarized as crossing, diverting, step over, and stopping based on a great number of numerical and experimental analysis with plain strain assumptions. However, under practical situations, the geometries of natural and hydraulic fractures are much more complex than the vertical and rectangular shape assumed by 2D models. The experimental studies on the role of height and inclination of natural fractures have revealed some other phenomena (e.g., bypassing process that the fluid-driven hydraulic fracture propagates up the back side of the natural fracture), which are unable to be captured in 2D. To better describe the intersection behaviors among different kind of fractures, a fully 3D model based on the displacement discontinuity method (DDM) is developed on top of our previous models, which only considered the propagation of hydraulic fractures. A novel crossing criterion to judge whether the hydraulic fracture will cross the cemented natural fracture in 3D is proposed. The successive node snapping scheme is adopted to construct conforming meshes for the evolving intersected curves between hydraulic and natural fracture surfaces, which only alters the location of a small fraction of nodes without changing the nodal connectivity. With this model, the evolution of fracture geometry after the hydraulic fracture intersects with the natural fractures of different toughness, size, orientation, and number is investigated. Because an extra dimension is considered, the fractures are allowed to propagate in more directions, resulting in a series of complex fracture geometries. The dynamic grid evolution method proposed in this work can promote the development of DDM in modeling fully 3D fracture networks in naturally fractured reservoirs.