The recovery of unconventional natural gas is a potential solution to the increasing worldwide energy demand and therefore plays a crucial role in the global energy landscape. However, the rapid reduction of production often experienced during the initial recovery phase of unconventional natural gas resources is a major concern. Therefore, an advanced understanding of realistic fracture characteristics and flow behaviour in hydraulically fractured shale and siltstone formations has become a subject of interest. This paper reports on the adoption of 3-D synchrotron imaging, 3-D fracture surface scanning, and statistical analysis to study the fracture morphology and characteristics of hydraulically induced fractures. The fractures generated in siltstone specimens exhibited fracture surfaces with high surface roughness (Joint Roughness Coefficients (JRCs) of 9–12) compared to shale formations (JRCs of 1.3–1.7). In addition, whatever the type of formation, hydraulic fracturing generates fractures with varying fracture profiles and fracture complexities. 3-D synchrotron imaging was utilized to measure the tortuosity of fractured specimens. Flow behaviour in proppant-filled fractures was studied to evaluate the influence of different proppant concentrations, fracture tortuosities, and confining stresses. Importantly, for low-proppant concentrations and high confining stress levels, the severity of fracture tortuosity determines the overall flow behaviour in fractures. The results reveal that fracture permeability increases by a magnitude of 20.62 and 28.4 darcy, when fracture tortuosity varied from 8.4 to 3.8 and 7.4 to 3.2, respectively. Furthermore, an increase of proppant concentration from 40 to 80% proppant coverage increased fracture permeability by a magnitude of 40.81 darcy, whatever the tortuosity of the fracture. 3-D synchrotron imaging of fractured permeability-tested specimens detected the greater crushing of proppants in low proppant-concentrated fractures than higher proppant-concentrated fractures.

非常规天然气的回收是解决日益增长的全球能源需求的潜在解决方案，因此在全球能源格局中发挥着至关重要的作用。然而，在非常规天然气资源的初始回收阶段经常出现产量的快速下降是一个主要问题。因此，深入了解水力压裂页岩和粉砂岩地层中的真实裂缝特征和流动行为已成为一个令人感兴趣的主题。本文报道了采用3-D同步加速器成像、3-D裂缝表面扫描和统计分析来研究水力致裂缝的裂缝形态和特征。与页岩地层（JRC 为 1.3-1.7）相比，粉砂岩试样中产生的裂缝显示出具有高表面粗糙度（联合粗糙度系数（JRC）为 9-12）的裂缝表面。此外，无论何种类型的地层，水力压裂都会产生具有不同裂缝剖面和裂缝复杂性的裂缝。3-D 同步加速器成像用于测量断裂试样的曲折度。研究了支撑剂填充裂缝中的流动行为，以评估不同支撑剂浓度、裂缝曲折度和围压的影响。重要的是，对于低支撑剂浓度和高围压水平，裂缝曲折的严重程度决定了裂缝中的整体流动行为。结果表明，裂缝渗透率增加了 20.62 和 28.4 达西，当骨折曲折度分别从 8.4 到 3.8 和 7.4 到 3.2 变化时。此外，支撑剂浓度从 40% 增加到 80% 的支撑剂覆盖率使裂缝渗透率增加了 40.81 达西，无论裂缝的曲折度如何。裂缝渗透率测试样本的 3-D 同步加速器成像检测到支撑剂浓度低的裂缝中支撑剂的破碎程度高于支撑剂浓度高的裂缝。