Pore-Scale Geodynamical Modelling

许多重要的地球物理和地质现象发生在充满流体的多孔岩石中。例子包括大洋中脊以下的上地幔和岩浆房中的熔融体运输。此外，流体相的存在会影响大块岩石的材料性质，进而影响我们用于研究这些系统的测量结果——地震速度和电导率都受到流体含量的影响。地质多孔介质表现出非常丰富的行为范围。在地球上地幔，在地质时间尺度上，固体基质表现得像一种非常粘稠的液体，因此在孔隙可以通过系统运输的地方会发生压实作用。在“糊状层”中，流体和固相可以通过凝固和熔化交换，这会影响流体的浮力和基体的渗透性。当地震波穿过充满流体的岩石时，流体和固体基质相互作用，影响地震波的传播。由于孔隙的复杂性和多孔系统的范围，通常在连续体水平上处理这些系统-单个孔隙不被分解，孔隙度被视为平均方程中的一个场。这些方程的例子包括用于描述具有延性基质的多孔系统的压实方程和用于描述多孔弹性系统的Biot方程。这些方程组广泛应用于地球物理和工程的各个领域。然而，在他们的推导中有许多假设没有经过严格的检验。近年来兴起了“数字岩石性质”这一领域，该领域将真实岩石的孔隙尺度图像作为数值模拟的建模域，在孔隙尺度上计算流体的行为。如果使用足够大的模拟域，这些计算可以用来计算多孔系统的有效性质。这些计算还具有阐明基本孔隙尺度机制的优点。在这个提案中，我描述了一个研究过程，在这个过程中，我和我的团队将使用连续尺度多孔介质方程来研究与地球相关的新效应，并使用孔隙尺度建模来测试连续尺度理论并确定有效材料特性。特别是，我将使用孔隙尺度模拟来确定Biot描述孔隙弹性的方程中的约束系数。我还建议测试许多关于压缩理论的缺乏约束的假设。由于实体矩阵在这些情况下是可变形的，因此我将使用允许变形模拟几何的高级数值方法。这将是有史以来第一次对压实系统的孔隙尺度模拟，将用于测试这些方程并确定有效特性，这将增加我们对这些重要地球材料的理解。

Many important geophysical and geological phenomena take place in fluid-filled porous rocks. Examples include the transport of melts in Earth's upper mantle below mid-ocean ridges and in magma chambers. Additionally, the presence of fluid phases affects the material properties of bulk rocks which in turn affect the measurements that we can use to investigate these systems - seismic velocity and electrical conductivity are both affected by fluid content. Geological porous media exhibit a very rich range of behavior. In Earth's upper mantle, on geological time scales, the solid matrix behaves like a very viscous liquid and so effects of compaction can occur where pores can be transported through the system. In "mushy layers", the fluid and solid phases can be exchanged through solidification and melting which can affect the buoyancy of the fluid and the permeability of the matrix. When seismic waves pass through fluid filled rocks, the fluids and solid matrix exert forces on one another that affect the propagation of these waves. Because of the complexity of pores and the extent of porous systems, it is common to treat these systems on a continuum level - individual pores are not resolved and the porosity is treated as a field in averaged equations. Examples of these equations include the compaction equations used to describe porous systems with ductile matrices and Biot's equations used to describe poro-elastic systems. These systems of equations are widely used in diverse fields of geophysics and engineering. However, there are many assumptions made in their derivations that have not been rigorously tested. In recent years, the field of "digital rock properties" has emerged in which pore scale imagery of real rocks is used as a modeling domain in a numerical simulation in which the behavior of fluids is calculated at the pore scale. If a sufficiently large simulation domain is used, these calculations can be used to calculate effective properties of porous systems. These calculations also have the advantage of elucidating the basic pore-scale mechanisms. In this proposal, I describe a course of research in which my group and I will use the continuum-scale porous medium equations to investigate novel effects that are relevant to the earth and use pore scale modeling to test continuum-scale theories and to determine effective material properties. In particular, I will be using pore-scale simulations to determine poorly constrained coefficients in Biot's equations describing poro-elasticity. I also propose to test many of the poorly constrained assumptions regarding compaction theory. Since the solid matrix is deformable in these cases, I will use advanced numerical methods that allow for a deforming simulation geometry. These will be the first ever pore scale simulations of compaction systems which will be used to test these equations and determine effective properties which will increase our understanding of these important earth materials.