Page 128 - Petrophysics 2E

PERMEABILITY 101

consequently, the sum of the effective permeabilities of all the phases
will always be less than the absolute permeability.
In presence of more than one fluid in the rock, the ratio of effective
permeability of any phase to the absolute permeability of the rock is
known as the "relative" permeability (kr) of that phase. For example,
the relative permeability of the oil, gas, and water would be kro = k&,
krg = k,,, km = k,/k respectively.

CLASSIFICATION OF PERMEABILIN

Petroleum reservoirs can have primary permeability, which is also
known as the matrix permeability, and secondary permeability. Matrix
permeability originated at the time of deposition and lithification
(hardening) of sedimentary rocks. Secondary permeability resulted from
the alteration of the rock matrix by compaction, cementation, fracturing,
and solution.
Whereas compaction and cementation generally reduce the
permeability, as shown in Figure 3.6, fracturing and solution tend
to increase it [13]. In some reservoir rocks, particularly low-porosity
carbonates, secondary permeability provides the main flow conduit for
fluid migration, e.g., in the Ellenburger Field, Texas.

Porosity = 36% Porosity = 36%
Horizontal permeability, Horizontal permeability,
KH = 1,000 mD KH = 100 mD
Vertical permeability, Vertical permeability,
KV = 600 mD KV = 25 mD

Sand Grains without Clay Sand Grains Without Clay

Cementing Material Cementing Material
Figure 3.6. Effects of clay cementing material on porosity and permeability [13].