Page 112 - Percolation Models for Transport in Porous Media With

Chapter 6

Determination of Pore Size

Distribution in Grained and

Cavernous Rocks

It follows from the results presented above that the quantities E, K, ki are deter-
mined primarily by the function f(r). Therefore the first thing to know for the
calculation of permeabilties is the size probability density function (PDF) for the
pore channels.
At present practical determination of the coefficients of permeability is carried
out mainly by means of direct experiments [72]. These, however, are too com-
plicated and cumbersome. An alternative approach suggests the development of
indirect methods for the determination of transfer coefficients, the most important
of which are K and ki. These methods should be based on model theoretical per-
ceptions of the pore space of the medium and the fluid flow. Information about
the pore space structure required by these methods can be obtained using one of
the known porometric methods for the chosen model of the medium.
The purpose of the porometric methods is to determine the size probability
density function (PDF) for the pores. The meaning of this function depends on
the model of the pore space structure used to interpret the porometric data. The
model of infinite cylindrical pores (ICP), which the majority of the contemporary
schemes of the porometric data interpretation is based upon, is too inaccurate and
can bring about considerable errors (73). To take account of specific properties of
the pore space structure of actual media more adequately, it is necessary to use
network models and percolation models to interpret the porometric data.
Many actual media (e.g., grained or cavernous ones) have twofold porosity,
i.e., large-scale, or porous, and small-scale, or capillary (47]. Volumetric proper-

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