Gravity drainage is known as the controlling mechanism of oil recovery in naturally fractured reservoirs. The efficiency of this mechanism is controlled by block-to-block interactions through capillary continuity and/or reinfiltration processes. In this study, at first, several free-fall gravity drainage experiments were conducted on a well-designed three-block apparatus and the role of tilt angle, spacers’ permeability, wettability and effective contact area (representing a different status of the block-to-block interactions between matrix blocks) on the recovery efficiency were investigated. Then, an experimental-based numerical model of free-fall gravity drainage process was developed, validated and used for monitoring the saturation profiles along with the matrix blocks. Results showed that gas wetting condition of horizontal fracture weakens the capillary continuity and in consequence decreases the recovery factor in comparison with the original liquid wetting condition. Moreover, higher spacers’ permeability increases oil recovery at early times, while it decreases the ultimate recovery factor. Tilt angle from the vertical axis decreases recovery factor, due to greater connectivity of matrix blocks to vertical fracture and consequent channelling. Decreasing horizontal fracture aperture decreases recovery at early times but increases the ultimate recovery due to a greater extent of capillary continuity between the adjacent blocks. Well match observed between the numerical model results and the experimental data of oil recovery makes the COMSOL multiphysics model attractive for application in multi-blocks fractured systems considering block-to-block interactions. The findings of this research improve our understanding of the role of different fracture properties on the block-to-block interactions and how they change the ultimate recovery of a multi-block system.

中文翻译：

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三块系统重力排水试验与建模研究

重力泄油被认为是天然裂缝性油藏采油的控制机制。这种机制的效率由通过毛细管连续性和/或再渗透过程的块间相互作用控制。本研究首先在精心设计的三块装置上进行了多次自由落体重力排水实验，研究了倾斜角、隔板渗透性、润湿性和有效接触面积（代表块的不同状态）的作用。基质块之间的相互作用）对回收效率的影响进行了研究。然后，开发、验证了基于实验的自由落体重力排水过程数值模型，并将其用于监测与矩阵块一起的饱和度剖面。结果表明，与原始液体润湿条件相比，水平裂缝的气体润湿条件削弱了毛细管的连续性，从而降低了采收率。此外，较高的隔层渗透率会在早期增加石油采收率，同时降低最终采收率。与垂直轴的倾斜角降低了采收率，因为基质块体与垂直裂缝的连通性更大，随后会形成通道。水平裂缝孔径的减小会降低早期的采收率，但由于相邻块体之间毛细管连续性的程度更大，因此会增加最终采收率。观察到的数值模型结果与石油采收率实验数据之间的良好匹配使得 COMSOL 多物理场模型对于考虑区块与区块相互作用的多区块裂缝系统的应用具有吸引力。这项研究的结果提高了我们对不同裂缝特性对区块间相互作用的作用以及它们如何改变多区块系统的最终采收率的理解。