Collaborative Research: Permeability Enhancement by Fluid Pressure Oscillations

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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.