Page 537 - Petrophysics

504 PETROPHYSJCS: RESERVOIR ROCK PROPERTIES

@f = fracture porosity, fraction
@m = matrix porosity, fraction
Swf = water saturation in fractures, fraction
Swm = water saturation in matrix, fraction
Bo = oil formation volume factor, bbl/STB.

Fracture porosity can be expressed as the ratio of the fracture pore
volume (Vpf) over the total bulk volume (Vbt):
VPf
Of = - (8.4a)
Vbt

The total porosity is:

(8.4b)

The sonic log only measures the matrix porosity. However, neutron
porosity is the combination of both the matrix and fracture porosity.
Thus fracture porosity can be estimated from well logs as [22]:

Fracture porosity can also be estimated with the help of well test analysis
in such reservoirs, using Equation 8.76.
Aguilera developed the following equation that relates the total
formation resistivity factor, Ft, for dual porosity systems, to the total
porosity based on the Pirson model of fully water-saturated rocks [23]:

where Ro is the resistivity of porous rock 100 percent saturated with
brine, and Rw is the formation water resistivity, both expressed in
Ohm-m.
If only the matrix porosity is present in the system, the porosity
partitioning coefficient, v, is equal to zero. Thus Equation 8.6 simplifies
to Equation 8.7, which is the same as for a consolidated matrix:

If only fracture porosity is present in the system, such as in Type-1
naturally fractured reservoirs, the porosity the partitioning coefficient