Collaborative Research: Permeability Enhancement by Fluid Pressure Oscillations

该项目将调查地壳浅层区域岩石内部的流体流动，从地表到约10公里。我们的工作将集中在动态应力，例如由地震波引起的，如何改变地壳的流动特性。以前的研究表明，当岩石在地震中摇晃时，流体渗透率会发生巨大变化。强震的影响可以估计，但弱震的影响，例如由于遥远的地震，就不太清楚了。我们将进行实验室实验来研究动态应力引起的瞬态和永久渗透率变化的过程和机制。实验室工作将结合理论和数值方法来开发渗透率变化的概念和定量模型。地震中产生的弹性波可以引发一系列现象，包括地震活动、火山爆发和间歇泉活动。通过地震波（或其他来源的瞬态载荷）传递的动态应力也会增加弹簧流量、溪流中的流体流量和石油产量，在某些情况下，自然系统的有效渗透率会增加三倍。这些观察结果归因于震动引起的浅层含水层渗透率变化。然而，动应力对岩石孔隙力学特性的影响机制和影响机制尚不清楚。在这里，我们建议采用多学科方法研究动态应力增强渗透率。我们的初步工作表明，在流体压力振荡作用下，裂缝岩石的渗透率明显提高。拟议的工作将扩大实验室数据，同时发展理论和关注潜在的机制。我们将利用在实验室中操作的过程和机制的知识来解决将我们的结果升级到现场条件的问题。我们提出了一系列基于自然系统观测的实验和模型，以(1)建立控制变量与由此导致的渗透率变化之间的明确关系，(2)分析增强的物理特性并确定潜在的过程，(3)建立可应用于实验室和现场尺度的结果的适当数值模型。所提出的实验结果有望对了解地壳中的流体流动和地震危险性产生重大影响。了解渗透率瞬态变化的物理基础将有助于改进油藏和水文应用的工程方法。

This project will investigate fluid flow within rock masses in the shallow regions of Earth's crust, from the surface to ~10 km. Our work will focus on how dynamic stresses, for example caused by seismic waves, change flow properties of Earth's crust. Previous work shows that fluid permeability can change dramatically when rocks are shaken during earthquakes. The effects of strong shaking can be estimated, but the effects of weak shaking, for example due to a distant earthquake, are less well understood. We will perform laboratory experiments to investigate the processes and mechanisms that cause transient and permanent permeability changes due to dynamic stressing. The lab work will be coupled with theory and numerical methods to develop conceptual and quantitative models for permeability changes. Elastic waves produced during earthquakes can trigger a range of phenomena including seismicity, volcanic eruptions, and geyser activity. Dynamic stressing via the passage of seismic waves (or from other sources of transient loads) can also increase spring discharge, fluid flow in streams, and oil production, in some cases tripling the effective permeability of the natural system. These observations have been attributed to shaking-induced changes in permeability of shallow aquifers. However, the underlying mechanisms and the affect of dynamic stresses on poromechanical properties of rocks are poorly understood. Here we propose to investigate permeability enhancement by dynamic stressing using a multidisciplinary approach. Our preliminary work shows clear evidence of permeability enhancement in fractured rock subject to fluid pressure oscillations. The proposed work will expand the laboratory data while developing the theory and focusing on the underlying mechanisms. We will use knowledge of the processes and mechanisms operative in the laboratory to address the problem of upscaling our results to field conditions. We propose a series of experiments and models informed by observations of natural systems to (1) establish clear relationships between the controlling variables and the resulting changes in permeability, (2) analyze the physics of the enhancement and identify the underlying processes and (3) build appropriate numerical models of the results that can be applied at the laboratory and field scales. Results of the proposed experiments are expected to have significant impact on understanding fluid flow in the Earth's crust and seismic hazard. Understanding the physical basis for transient changes in permeability will lead to improved engineering approaches for oil reservoir and hydrological use.