Summary The discrete fracture network (DFN) model is widely used to simulate and represent the complex fractures occurring over multiple length scales. However, computational constraints often necessitate that these DFN models be upscaled into a dual-porosity dual-permeability (DPDK) model and discretized over a corner-point grid system, which is still commonly implemented in many commercial simulation packages. Many analytical upscaling techniques are applicable, provided that the fracture density is high, but this condition generally does not hold in most unconventional reservoir settings. A particular undesirable outcome is that connectivity between neighboring fracture cells could be erroneously removed if the fracture plane connecting the two cells is not aligned along the meshing direction. In this work, we propose a novel scheme to detect such misalignments and to adjust the DPDK fracture parameters locally, such that the proper fracture connectivity can be restored. A search subroutine is implemented to identify any diagonally adjacent cells of which the connectivity has been erroneously removed during the upscaling step. A correction scheme is implemented to facilitate a local adjustment to the shape factors in the vicinity of these two cells while ensuring the local fracture intensity remains unaffected. The results are assessed in terms of the stimulated reservoir volume calculations, and the sensitivity to fracture intensity is analyzed. The method is tested on a set of tight oil models constructed based on the Bakken Formation. Simulation results of the corrected, upscaled models are closer to those of DFN simulations. There is a noticeable improvement in the production after restoring the connectivity between those previously disconnected cells. The difference is most significant in cases with medium DFN density, where more fracture cells become disconnected after upscaling (this is also when most analytical upscaling techniques are no longer valid); in some 2D cases, up to a 22% difference in cumulative production is recorded. Ignoring the impacts of mesh discretization could result in an unintended reduction in the simulated fracture connectivity and a considerable underestimation of the cumulative production.

中文翻译：

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分析网格划分和网格对齐在双孔双渗透升级中的影响

总结 离散裂缝网络 (DFN) 模型被广泛用于模拟和表示出现在多个长度尺度上的复杂裂缝。然而，计算约束通常需要将这些 DFN 模型升级为双孔隙度双渗透率 (DPDK) 模型并在角点网格系统上离散化，这在许多商业模拟包中仍然普遍实施。只要裂缝密度高，许多分析放大技术都适用，但这种情况通常不适用于大多数非常规油藏环境。一个特别不希望的结果是，如果连接两个单元的裂缝平面未沿网格方向对齐，则可能会错误地移除相邻裂缝单元之间的连通性。在这项工作中，我们提出了一种新的方案来检测这种错位并局部调整 DPDK 断裂参数，从而可以恢复适当的断裂连接性。执行搜索子程序以识别在放大步骤期间其连通性已被错误移除的任何对角相邻单元。实施校正方案以促进对这两个单元附近的形状因子进行局部调整，同时确保局部裂缝强度不受影响。根据增产储层体积计算对结果进行评估，并分析对裂缝强度的敏感性。该方法在一组基于 Bakken 组构建的致密油模型上进行了测试。校正后的放大模型的模拟结果更接近于 DFN 模拟的结果。在恢复那些先前断开的单元之间的连接后，生产有明显的改善。这种差异在中等 DFN 密度的情况下最为显着，其中更多的裂缝单元在放大后断开（这也是大多数分析放大技术不再有效的时候）；在某些二维情况下，记录的累积产量差异高达 22%。忽略网格离散化的影响可能会导致模拟裂缝连通性的意外减少和累积产量的严重低估。在放大后更多的断裂单元变得断开（这也是大多数分析放大技术不再有效的时候）；在某些二维情况下，记录的累积产量差异高达 22%。忽略网格离散化的影响可能会导致模拟裂缝连通性的意外减少和累积产量的严重低估。在放大后更多的断裂单元变得断开（这也是大多数分析放大技术不再有效的时候）；在某些二维情况下，记录的累积产量差异高达 22%。忽略网格离散化的影响可能会导致模拟裂缝连通性的意外减少和累积产量的严重低估。