Page 525 - Petrophysics

a) Regional fracture patterns found in Jurassic Navajo sandstone, Lake
Powell, southern Utah.
P -.-. ' 1

b) Conjugate shear fractures corresponding to a tectonic fracture system in an
outcrop from Wyoming.

c) Crack network observed in mud.
Figure 8.2. a, b, c. Different fracture systems in mud, and rocks. After Lui et al. [8J.

result of mineralization. However, in most fracture modeling studies
fractures are considered as open and they have a positive impact
on the fluid flow. A sealed small natural fracture may even be
undetectable.
Nelson identified four types of naturally fractured reservoirs, based on
the extent to which fractures have altered the porosity and permeability
of the reservoir matrix [ 11 :

Type 1: In type 1 reservoirs, fractures provide all the reservoir storage
capacity and permeability. The Amal field in Libya, the IaPaz and Mara
fields in Venezuela, and Pre-Cambrian basement reservoirs in eastern
China are notable type 1 reservoirs (Figure 8.5a).