Numerical and Experimental Studies of Particle Settling in Real Fracture Geometries
Numerical and Experimental Studies of Particle Settling in Real Fracture Geometries
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DOI：
10.1007/s00603-016-1100-3
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发表时间：
2016-09
影响因子：
6.2
通讯作者：
Pratanu Roy;Wyatt L. Du Frane;Y. Kanarska;S. Walsh
中科院分区：
文献类型：
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作者：
Pratanu Roy;Wyatt L. Du Frane;Y. Kanarska;S. Walsh
支撑剂是水力增产作业的重要组成部分，通过保持裂缝孔径来提高导流能力。虽然正确的放置是确保支撑剂有效发挥作用的必要组成部分，但人们对支撑剂在天然岩石裂缝中的运输行为知之甚少。特别是，随着公司追求涉及新型支撑剂的新支撑策略，需要更准确的支撑剂行为模型来帮助指导其部署。模拟泥浆规模的支撑剂行为的主要困难在于，传统上用于表示大规模泥浆行为的连续体模型在裂缝几何形状中的适用性不强。颗粒传输模型通常基于与水力压裂操作中发现的裂缝相同规模或更大的代表性体积，使得它们不适合对这些类型的流动进行建模。在缺乏第一原理方法的情况下，需要经验闭合关系。然而，即使是这样的经验闭合关系，在没有对颗粒水平上的支撑剂行为的准确理解的情况下也难以导出。因此，需要能够探测亚断裂尺度的现象的实验和模拟。在本文中，我们提出的结果，从实验和数值研究调查支撑剂的行为在子裂缝水平，特别是颗粒分散在支撑剂沉降过程中的作用。在实验研究中，三维打印技术被用来准确地再现颗粒流动池内的断裂Marcellus页岩样品的拓扑结构。通过在透明塑料树脂中重建表面，可以直接真实的跟踪裂缝内的支撑剂运动，而不需要X射线成像。通过使用透明和不透明支撑剂类似物的混合物，进一步增强颗粒追踪。伴随的数值研究采用高保真三维颗粒流模型，能够明确表示的颗粒，裂缝表面和间隙流体流。这两项研究都揭示了颗粒沉降过程中的大尺度涡旋运动。在大多数情况下，这种行为是独立的裂缝拓扑结构，而是由下沉颗粒和上涌间隙流体之间的相互作用驱动。这种运动导致大量的颗粒分散，明显大于传统浆料模型的预期。颗粒和流体之间的竞争还导致颗粒朝向裂缝壁的重新分布，这对于支撑剂沿着裂缝的输送具有重要意义。
Proppant is a vital component of hydraulic stimulation operations, improving conductivity by maintaining fracture aperture. While correct placement is a necessary part of ensuring that proppant performs efficiently, the transport behavior of proppant in natural rock fractures is poorly understood. In particular, as companies pursue new propping strategies involving new types of proppant, more accurate models of proppant behavior are needed to help guide their deployment. A major difficulty with simulating reservoir-scale proppant behavior is that continuum models traditionally used to represent large-scale slurry behavior loose applicability in fracture geometries. Particle transport models are often based on representative volumes that are at the same scale or larger than fractures found in hydraulic fracturing operations, making them inappropriate for modeling these types of flows. In the absence of a first-principles approach, empirical closure relations are needed. However, even such empirical closure relationships are difficult to derive without an accurate understanding of proppant behavior on the particle level. Thus, there is a need for experiments and simulations capable of probing phenomena at the sub-fracture scale. In this paper, we present results from experimental and numerical studies investigating proppant behavior at the sub-fracture level, in particular, the role of particle dispersion during proppant settling. In the experimental study, three-dimensional printing techniques are used to accurately reproduce the topology of a fractured Marcellus shale sample inside a particle-flow cell. By recreating the surface in clear plastic resin, proppant movement within the fracture can be tracked directly in real time without the need for X-ray imaging. Particle tracking is further enhanced through the use of mixtures of transparent and opaque proppant analogues. The accompanying numerical studies employ a high-fidelity three-dimensional particle-flow model, capable of explicitly representing the particles, the fracture surface and the interstitial fluid flow. Both studies reveal large-scale vortex motion during particle settling. For the most part, this behavior is independent of the fracture topology, instead driven by interactions between the sinking particles and the upwelling interstitial fluid. This motion results in large amounts of particle dispersion, significantly greater than might be expected from traditional slurry models. The competition between the particles and the fluid also results in a redistribution of particles toward the fracture walls, which has significant implications for the transport of proppant along the fracture.