Summary Shale wells are often shut in after hydraulic fracturing is completed. Shut-in often lasts for an extended period in the perceived hope of improving the ultimate oil recovery. However, current literature does not show a strong consensus on whether shut-in will improve ultimate oil recovery. Because of the delayed production, evaluating the benefits of shut-in in improving the ultimate oil recovery is crucial. Otherwise, shut-in would merely delay the production and harm the economic performance. In this paper, we use a numerical flow-geomechanical modeling approach to investigate the effect of imbibition on shut-in potentials to improve the ultimate oil recovery. We propose that imbibition is one of the strongly confounding variables that causes mixed conclusions in the related literature. The investigation methodology involves probabilistic forecasting of three reservoir realization models validated based on the same field production data. Each of the models represents different primary recovery-driving mechanisms, such as imbibition-dominant and compaction-dominant recovery. A parametric study is conducted to explore and identify the specific reservoir conditions in which shut-in tends to improve shale oil recovery. Ten reservoir parameters that affect the imbibition strength are studied under different shut-in durations. Comparison among the three models quantitatively demonstrates that shut-in tends to improve both the ultimate oil recovery and net present value (NPV) only if the shale reservoir demonstrates imbibition-dominant recovery. A correlation among ultimate oil recovery, flowback efficiency, and NPV also shows that there is no strong relationship between flowback efficiency and ultimate oil recovery. This study is one of the first to emphasize the importance of quantifying the imbibition strength and its contribution in helping recover the shale oil for optimum flowback and shale well shut-in design after hydraulic fracturing.

中文翻译：

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关井过程中渗吸和压实对最终页岩油采收率的影响：数值研究

总结 页岩井通常在水力压裂完成后关闭。关闭通常会持续很长时间，以期提高最终石油采收率。然而，目前的文献并未就关井是否会提高最终采收率达成强烈共识。由于延迟生产，评估关井在提高最终石油采收率方面的好处至关重要。否则，关停只会耽误生产，损害经济效益。在本文中，我们使用数值流动-地质力学建模方法来研究渗吸对关井潜力的影响，以提高最终采收率。我们认为，自吸是在相关文献中导致混合结论的强烈混淆变量之一。调查方法涉及基于相同油田生产数据验证的三个储层实现模型的概率预测。每个模型都代表不同的主要恢复驱动机制，例如吸胀主导和压实主导恢复。进行了一项参数研究，以探索和确定关井有助于提高页岩油采收率的特定储层条件。研究了不同关井时间下影响自吸强度的十个储层参数。三种模型之间的比较定量地表明，只有在页岩储层表现出吸吸主导采收率的情况下，关井才能同时提高最终采收率和净现值 (NPV)。最终采油率、返排效率、NPV 也表明返排效率和最终采收率之间没有很强的关系。这项研究是第一个强调量化自吸强度的重要性及其在帮助回收页岩油以实现水力压裂后的最佳回流和页岩井关井设计方面的贡献之一。