Page 140 - Petrophysics 2E

PERMEABILITY-POROSITY RELATIONSHIPS 113

flow unit as a reservoir zone that is laterally and vertically continuous,
and has similar permeability, porosity, and bedding characteristic [22].
Gunter et al. defined flow unit as a stratigraphically continuous interval
of similar reservoir process that honors the geologic framework and
maintains the characteristic of the rock type [23].
From these definitions, the flow units have the following
characteristics:

1. A flow unit is a specific volume of reservoir, composed of one or more
reservoir quality lithologies.
2. A flow unit is correlative and mapable at the interval scale.
3. A flow unit zonation is recognizable on wire-line log.
4. A flow unit may be in communication with other flow units.

Gunter et al. introduced a graphical method for quantifying reservoir flow
units based on geological framework, petrophysical rock/pores types,
storage capacity, flow capacity, and reservoir process speed. According
to them, the five steps for identifying and characterizing flow units
are [23]:

1. Identify rock type and illustrate the Withland porosity-permeability
cross plot (Figure 3.14).
2. Construct the stratigraphic modified Lorenz plot (SMLP) by computing
on a foot-foot basis the percent flow capacity (permeability thickness)
and percent flow storage (porosity thickness) (Figure 3.15).
3. Select flow unit intervals based on inflection points from SMLP.
These preliminary flow units must be verified using the SFP geologic
framework R35 (calculated pore throat radius (pm) at 35% mercury
saturation) curve and K/@ ratio.

Porosity, +,%
Figure 3.14. Sketch of K-@ Withlandplot r.231.