Abstract It is important yet challenging to effectively and accurately predict the recovery of fractured reservoirs. Among numerous fractured reservoir simulation models, the embedded discrete fracture model (EDFM) is the most outstanding one for it incorporates the discrete fractures into structured grids of the matrix, which precisely describes the arbitrarily distributed fractures while not increasing the gridding and calculation complexity. However, the current EDFM still possesses drawbacks for its structured grid shows poor adaptivity to irregularly shaped reservoirs, and also causes a sharp pressure gradient between the matrix and fractures and weakens the simulation accuracy. To conquer the drawbacks of the current EDFM, an unstructured quadrangular grid-based EDFM (UnQ-EDFM) is proposed in this paper. In this model, a frontal Delaunay quadrangular grid is adopted that could perfectly adapt to irregular reservoir boundaries without increasing the grid number and gridding complexity; besides, local grid refinement could be achieved flexibly in anywhere of the reservoir, which effectively alleviates the simulation error while not adding too much calculation. Based on the UnQ-EDFM, the production of a multi-stage hydraulic fractured well in irregular shaped naturally fractured shale gas reservoir is simulated, the simulation results under different types of grids are compared. Furthermore, an optimization framework that applies WOA as the optimization algorithm and NPV as the objective function is constructed, the hydraulic fractured well in the above-mentioned reservoir is optimized and the reliability of the UnQ-EDFM is testified through thousands of times of simulation. The results of simulation and optimization demonstrate the reliability and superiority of the UnQ-EDFM over the traditional structured grid-based EDFM, for it adapts to complex-shaped reservoirs, maintains high simulation accuracy, and reduces simulation time, simultaneously. The UnQ-EDFM proposed in this paper severs as an efficient tool and contributes to the precise and efficient simulation for the fractured reservoirs’ development.

中文翻译：

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基于非结构化四边形网格的高效嵌入式离散断裂模型

摘要 有效准确地预测裂缝性储层的采收率具有重要意义但也具有挑战性。在众多裂缝性储层模拟模型中，嵌入式离散裂缝模型（EDFM）最为突出，它将离散裂缝纳入矩阵的结构化网格中，在不增加网格化和计算复杂度的情况下，精确描述任意分布的裂缝。然而，目前的EDFM仍然存在缺陷，其结构网格对形状不规则的储层适应性差，并且在基质和裂缝之间造成急剧的压力梯度，削弱了模拟精度。为了克服当前EDFM的缺点，本文提出了一种基于非结构化四边形网格的EDFM（UnQ-EDFM）。在这个模型中，采用正面Delaunay四边形网格，在不增加网格数和网格复杂度的情况下，可以完美适应不规则的储层边界；此外，可以在储层的任何地方灵活地实现局部网格细化，有效地减轻了模拟误差，同时又不增加过多的计算量。基于UnQ-EDFM对不规则形状天然裂缝性页岩气藏多级水力压裂井的生产进行了模拟，比较了不同类型网格下的模拟结果。进一步构建了以WOA为优化算法、NPV为目标函数的优化框架，对上述油藏水力压裂井进行了优化，并通过数千次模拟验证了UnQ-EDFM的可靠性。仿真和优化结果证明了UnQ-EDFM相对于传统的基于结构网格的EDFM的可靠性和优越性，因为它适应复杂形状的储层，保持较高的仿真精度，同时减少了仿真时间。本文提出的UnQ-EDFM作为一种有效的工具，有助于对裂缝性储层的开发进行精确、高效的模拟。并同时减少模拟时间。本文提出的UnQ-EDFM作为一种有效的工具，有助于对裂缝性储层的开发进行精确、高效的模拟。并同时减少模拟时间。本文提出的UnQ-EDFM作为一种有效的工具，有助于对裂缝性储层的开发进行精确、高效的模拟。