Abstract The results of a systematic, micro-scale experimental investigation on two-phase gas/brine flow through proppant-packed fractured shale samples under increasing effective stresses of up to 5000 psi are presented in this paper. We use a miniature core-flooding apparatus integrated with a high-resolution X-ray micro-CT scanner to perform the flow experiments. Geomechanical deformation and its impact on displacement mechanisms governing fluid transport within the packed fractures are studied at the pore scale under certain flow and stress conditions. These conditions were carefully designed to represent reservoir depletion and transport of water through such media. Since proppant grains are placed to maintain the long-term conductivity of the induced fractures, they significantly influence the geomechanical and multi-phase flow behavior of these conduits during reservoir depletion. We particularly examined the effectiveness of modified resin-coated sand (compared to a basic white sand) in maintaining the hydraulic conductivity of induced fractures. Significant bullet-like embedment and proppant crushing under severe stress conditions were found to be the shortcomings of these proppants, respectively. We then developed a methodical framework to design improved proppants with a similar mechanical strength to the host shale rock to withstand these drawbacks. Sphericity, roundness, and size of the proppant grains also impacted the critical properties of the constructed pore space such as pore size distribution and pore-throat aspect ratio. Such parameters control pore-scale gas-to-brine and brine-to-gas displacements within the hydraulic fractures. We specifically studied the non-wetting phase trapping and its subsequent impact on reduction of available pore space for other fluids to flow. It was found that trapped gas globules are very likely to deform within the medium and redistribute/reconnect under a higher effective stress. For the first time, wettability alteration of the proppant pack from water-wet to oil-wet was observed in a gas/brine fluid system. Wettability alteration occurred non-uniformly and was thought to be due to deposition of the shale organic matter released after significant proppant embedment. Such wetting characteristics aggravate multi-phase trapping within the fractures, which in turn leads to dramatic reductions in effective gas permeability. This study is concluded with a set of recommendations that can be used to effectively maintain the productivity of propped fractures for extended period of time.

中文翻译：

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页岩气藏支撑剂填充裂缝：变形、润湿性和多相流效应的原位调查

摘要 本文介绍了在有效应力高达 5000 psi 的情况下，通过支撑剂填充的裂隙页岩样品的两相气/盐水流的系统、微尺度实验研究结果。我们使用与高分辨率 X 射线微 CT 扫描仪集成的微型岩心溢流装置来进行流动实验。在一定的流动和应力条件下，在孔隙尺度上研究了地质力学变形及其对控制填充裂缝内流体输送的位移机制的影响。这些条件经过精心设计，以代表水库枯竭和水通过此类介质的输送。由于放置支撑剂颗粒是为了保持诱导裂缝的长期导流能力，在储层枯竭期间，它们显着影响这些管道的地质力学和多相流动行为。我们特别研究了改性树脂包覆砂（与基础白砂相比）在维持诱导裂缝导水率方面的有效性。发现在严重应力条件下明显的子弹状嵌入和支撑剂破碎分别是这些支撑剂的缺点。然后，我们开发了一个有条不紊的框架来设计具有与宿主页岩相似的机械强度的改进支撑剂，以承受这些缺点。支撑剂颗粒的球形度、圆度和尺寸也会影响构建的孔隙空间的关键特性，例如孔径分布和孔喉纵横比。这些参数控制着水力裂缝中孔隙尺度的气-盐水和盐水-气置换。我们专门研究了非润湿相捕获及其对其他流体流动可用孔隙空间减少的后续影响。发现被困气球很可能在介质内变形并在更高的有效应力下重新分布/重新连接。首次在气体/盐水流体系统中观察到支撑剂充填层的润湿性从水湿变为油湿。润湿性改变发生不均匀，被认为是由于支撑剂大量嵌入后释放的页岩有机质沉积所致。这种润湿特性加剧了裂缝内的多相圈闭，进而导致有效气体渗透率显着降低。