Abstract
Using Fracture Seismic methods to map fluid-conducting fracture zones makes it important to understand fracture connectivity over distances greater 10–20 m in the Earth’s upper crust. The principles required for this understanding are developed here from the observations that (1) the spatial variations in crustal porosity are commonly associated with spatial variations in the magnitude of the natural logarithm of crustal permeability, and (2) many parameters, including permeability have a scale-invariant power law distribution in the crust. The first observation means that crustal permeability has a lognormal distribution that can be described as κ ≈ κ 0 exp ( α ( φ − φ 0 ) ) , where α is the ratio of the standard deviation of ln permeability from its mean to the standard deviation of porosity from its mean. The scale invariance of permeability indicates that αϕο = 3 to 4 and that the natural log of permeability has a 1/k pink noise spatial distribution. Combined, these conclusions mean that channelized flow in the upper crust is expected as the distance traversed by flow increases. Locating the most permeable channels using Seismic Fracture methods, while filling in the less permeable parts of the modeled volume with the correct pink noise spatial distribution of permeability, will produce much more realistic models of subsurface flow.
Highlights
As discussed by Sicking and Malin (2019) [1], new methods of passive seismic data acquisition and processing allow ambient subsurface fluid connectivity to be mapped
Exponent of Permeability the signal, S(k)) of each Fourier component is plotted against the logarithm of the spatial frequency, k, Prior to the invention of Fracture Seismics (FS) methods, it was not possible to image fracture permeability directly of the to component measured in cycles/km
Flow measurements are difficult to make at even a few meters from a drill hole
Summary
As discussed by Sicking and Malin (2019) [1], new methods of passive seismic data acquisition and processing allow ambient subsurface fluid connectivity to be mapped. The FS flow prediction was confirmed both by gas pressure communication and by a tracer These measurements showed a high degree of connectivity over ~600 m between vertical Well B and experiment. These measurements showed a high degree of connectivity over ~600 m between vertical horizontal Well A, as indicated by the FS backbone in the lower panel.
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