Laboratory for Applied Experimental Geophysics Department of Physics 

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Scaling Physics of Mechanical Deformation and Fluid Flow in Fractures

 

Background
    Fractures are mechanical discontinuities that are present at all length scales.  Mechanical discontinuities range in size from lattice dislocations (10-9 m) to micro-cracks (10-6) to fractures (1 m) to the scale of plate boundaries (104 m).  Any single site will encompass mechanical discontinuities over several orders of magnitude, and these are often perturbed by natural (e.g., earthquakes) and/or induced processes associated with subsurface projects.  Mechanical discontinuities dominate the flow of fluids and the mechanical behavior of all subsurface structures and processes.  Therefore, it is imperative to be able to characterize them at all scales, and to understand the coupling of the mechanical properties to the fluid flow properties.  In particular, the seismic visibility of a fracture (a mechanical property) might be able to detect and characterize fractures remotely and non-invasively, providing critical information on fluid flow properties.


Fracture Scales



    The objective of this proposal is to develop a universal scaling relationship between the hydraulic and mechanical properties of fractures, and to determine the effect of scale on the interpretation of seismic data from fractures or fractured systems.  To achieve this objective, we will perform a computationally-intensive parallelized-approach relating fluid flow through a fracture to fracture deformation and seismic wave interaction with the fracture, all as a function of scale.  This project will use four numerical approaches:  (1) a stratified percolation approach to generate pore-scale (10s-100s microns) fracture void geometry for fractures that span over least three orders of magnitude in length (0.1 to 100 m); (2) a combined conjugate-gradient method and fast-multipole method for determining fracture deformation; (3) a flow network model for simulating fluid flow, fluid velocity and fluid pressures within a fracture, and (4) a spectral-element code for implementing wave packets to probe, seismically, the fracture as a function of frequency and beam waist.










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