Flow in porous media in the weak inertia regime visualized by µ-PIV and MRI velocimetry

通过 µ-PIV 和 MRI 测速可视化弱惯性状态下多孔介质中的流动

• 批准号: 524644451
• 负责人: Dr. Sabina Haber-Pohlmeier
• 金额: --
• 依托单位: Institut für Bio- und Geowissenschaften (IBG)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/524644451?language=en
• 关键词: Flow; porous; media; weak; inertia

Our fundamental understanding of the evolution of the physical processes taking place during single- and multi-phase flow in fractured porous media is of elevated importance for the scientific community. In terms of real-life implications, a thorough understanding of such processes will enhance our applications inventory in the fields of subsurface hydrology, geophysics, reservoir engineering, and biomechanics. While low flow velocities in the creeping flow regime are best described by Darcy´s relation, additional terms of higher order must be considered for significantly increased velocities as proposed by Forchheimer. There has been a waste number of works for the purely creeping flow regime and the purely turbulent one, but not in between, and more specifically in the weak inertia regime, i.e. the transition between the two extremes. Given this lack of experimental evidence, we aim to map flow fields in the weak inertia regime in systems of increasing complexity from 2D to 3D at high spatial resolution. First, we investigate 2D micromodels with a single channel, a repeating channel-pore unit, and a 2D model fracture with rough pore surfaces. These systems allow the combination of 2D micro-particle imaging velocimetry (micro-PIV) with 3D flow-sensitive magnetic resonance imaging (MRI). To match the resolutions of both methods, MRI is also used to determine spatially resolved propagators that allow resolution of velocity fields within a voxel. They then serve as proxies for velocity fields and can be applied to 3D and opaque systems. In the second step, we investigate the first 3D system, a homogenous porous glass cylinder. At low velocities, one expects bulk effects through all pores in the sense of the Darcy relationship. As the Reynolds numbers increase, larger wake areas appear combined with stretched flow paths. The knowledge gained so far will now be used in the 2nd main part of the project for the investigation of fracked natural cores. To study flow, a natural rock core will be fractured vertically, a technique now available at the University of Stuttgart. With respect to MRI, this natural porous medium requires the use of a multi-slice bipolar gradient pair pulse sequence to minimize internal gradient effects. The difference to the model systems investigated so far is that the flow is controlled by water exchange between the pore system and the fracture. It is therefore to be expected that preferential flow patterns develop along with stationary areas with the transition from Darcy to weak inertia flow regime. These experimentally obtained 3D flow fields are then available to test and further develop theoretical approaches such as Forchheimer´s relation for their validity and limitations.

我们对裂缝多孔介质中单相流和多相流过程中发生的物理过程演化的基本了解对于科学界来说非常重要。就现实生活的影响而言，对此类过程的透彻理解将增强我们在地下水文学、地球物理学、油藏工程和生物力学领域的应用库存。虽然蠕动流态中的低流速最好由达西关系式描述，但如 Forchheimer 提出的，必须考虑更高阶的附加项以显着增加速度。对于纯粹的蠕动流态和纯粹的湍流流态，已经有大量的工作浪费了，但在两者之间，更具体地说，在弱惯性流态，即两个极端之间的过渡方面，却没有。鉴于缺乏实验证据，我们的目标是在高空间分辨率下绘制从 2D 到 3D 复杂性不断增加的系统中弱惯性状态下的流场。首先，我们研究具有单通道、重复通道-孔隙单元的二维微模型以及具有粗糙孔隙表面的二维模型裂缝。这些系统可将 2D 微粒成像测速 (micro-PIV) 与 3D 流敏磁共振成像 (MRI) 相结合。为了匹配两种方法的分辨率，MRI 还用于确定空间分辨传播器，从而允许体素内速度场的分辨率。然后，它们充当速度场的代理，并可应用于 3D 和不透明系统。第二步，我们研究第一个 3D 系统，即均质多孔玻璃圆柱体。在低速时，人们预计达西关系意义上的通过所有孔隙的体积效应。随着雷诺数的增加，出现更大的尾流区域以及拉伸的流动路径。迄今为止获得的知识现在将用于该项目的第二个主要部分，以调查压裂的天然岩心。为了研究流动，天然岩芯将被垂直断裂，斯图加特大学现在可以使用这项技术。对于 MRI，这种天然多孔介质需要使用多切片双极梯度对脉冲序列来最小化内部梯度效应。与迄今为止研究的模型系统的区别在于，流动是由孔隙系统和裂缝之间的水交换控制的。因此，预计随着从达西流态向弱惯性流态的转变，优先流型与静止区域一起发展。这些通过实验获得的 3D 流场可用于测试和进一步开发理论方法，例如 Forchheimer 关系式的有效性和局限性。