Page 567 - Petrophysics

534 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

(a) Fracture frequency (b) Fracture tortuosity
Figure 8.24. Examples of fracture frequency and fracture tortuosity.

Figure 8.25. Realistic and idealized naturally fractured rocks, regenerated after
Warren and Root fl8].

CHARACTERIZING NATURAL FRACTURES FROM
WELL TEST DATA

Warren and Root first modeled the transient flow of fluids in naturally
fractured rocks, assuming that the rock consists of a fracture network as
shown in Figure 8.25 [ 181. This widely popular model for flow analysis
in naturally fractured reservoirs is referred to as the “sugar cube model”
Warren and Root assumed that the entire fluid flows from the matrix to
the fractures and only fractures feed the wellbore.
Since not all naturally fractured reservoirs behave similarly, the degree
of fluid flow is controlled by the matrix and the fracture properties. Thus
Warren and Root introduced two key parameters to characterize naturally
fractured reservoirs:

(1) the storage capacity ratio, o, which is a measure of the fluid stored
in fractures as compared with the total fluid present in the reservoir;
and