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Now we will return to the expression (9) and make the
following two definitions: First, the dynamic tortuosity is given by

| |
(30) |

and, second, the inverse of the dynamic permeability is given by
| |
(31) |

This second expression can also be rewritten as
| |
(32) |

The motivations for both definitions can be seen in their limiting
values:
| |
(33) |

These results follow once it is recognized that the dynamic viscosity factor
has unity as its the limit when and,
although it can have differing numerical factors,
it always goes like for large
. We will give some examples of this
behavior in the next section.

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Stanford Exploration Project

7/8/2003