Page 527 - Petrophysics

INDICATORS OF NATURAL FRACTURES 495

Matrix Fractures Low Permeability Matrix Well
Figure 8.5. Types of naturally fractured reservoirs [IOJ.

These formations are significantly anisotropic and often uneconomic to
develop and produce.

INDICATORS NATURAL FRACTURES
OF

Stearns and Friedman reviewed the multiple roles played by fractures
in exploration and exploitation of naturally fractured reservoirs [4]. They
showed that fractures could alter the matrix porosity or the permeability,
or both. If the fractures or connected vugs are filled with secondary
minerals, they may restrict the flow. However, even in rocks of low
matrix porosity, fractures and solution channels increase the pore volume
by both increasing porosity and connecting isolated matrix porosity and
therefore help the recovery of petroleum fluids economically. Hence,
the ability to estimate a fracture’s density and its distribution of porosity
is essential for reservoir evaluation. One should keep in mind, however,
that fractures alone constitute less than 1% of the porosity [ll, 121.
Early recognition of a fractured reservoir and an estimate of its rock