Due to the existence of bedding planes in shale oil reservoirs, the complexity of crack networks created by conventional hydraulic fracturing (HF) technology is limited, resulting in low oil production. In this paper, a fatigue loading method was proposed to increase the complexity of the cracking network. The propagation behaviors of small cracks were investigated and compared under both monotonic and fatigue loading conditions by using SEM in-situ three-point bending tests. In addition, the influences of local micro mineral aggregates and stress ratios (R = 0.1, 0.3 and 0.5) on the propagation behavior of small fatigue cracks (SFCs) in shale were quantitatively evaluated. The SEM in-situ fatigue tests demonstrated the effectiveness of fatigue loading in enabling SFC to propagate through the bedding plane and increase crack network complexity from a micro perspective. A fitting exponential formula of the stress intensity factor range threshold ΔKth and stress ratio R was obtained. This study assists us in deeply understanding the influence of micro mineral aggregates and stress ratio on the SFC propagation mechanism and its implications for HF design in shale oil reservoirs.

中文翻译：

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应力比和局部微矿物聚集体对含层理面页岩中小疲劳裂纹扩展的影响


由于页岩油储层中存在层理面，传统水力压裂 （HF） 技术产生的裂缝网络的复杂性受到限制，导致石油产量低。本文提出了一种疲劳加载方法，以增加开裂网络的复杂性。采用 SEM 原位三点弯曲试验，对单调和疲劳载荷条件下小裂纹的扩展行为进行了研究和比较。此外，定量评价了局部微量矿物聚集体和应力比 （R = 0.1、0.3 和 0.5） 对页岩中小疲劳裂纹 （SFC） 扩展行为的影响。SEM 原位疲劳测试证明了疲劳载荷在使 SFC 能够通过层理平面传播并从微观角度增加裂纹网络复杂性方面的有效性。得到应力强度因子范围阈值 ΔKth 和应力比 R 的拟合指数公式。本研究有助于我们深入了解微矿物聚集体和应力比对页岩油储层SFC传播机制的影响及其对HF设计的影响。