Page 303 - Principles of Applied Reservoir Simulation 2E

288 Principles of Applied Reservoir Simulation

The top layer (K = 1) is shown. The second layer (K = 2) is below the K = 1
layer, and so on. The top of each gridblock may vary from one block to another.
This allows the model to perform calculations using grid representations of
reservoirs ranging from flat layer cake models to dipping structures such as
anticlines and domes. An anticlinal structure is shown in Figure 27-2.

D -6200-60001
D-6400-6200
• -6600-6400
•-6800-6600
North - South

Figure 27-2. Depth to top of anticlinal structure.

27.3 Petrophysical Model

Monitoring changes in the seismic characteristics of a reservoir as the
reservoir is produced is the basis of time-lapse (4D) seismic monitoring
[Anderson, etal., 1995; He, etal., 1996; Fanchi, etal. 1999]. Changes in seismic
characteristics are determined in WINB4D by calculating seismic attributes as
a function of time. The seismic attributes calculated in WINB4D are defined
below.

( ompressional and Shear Velocities
Seismic compressional velocity and shear velocity are calculated from
the expressions [Scho'n, 1996; McQuillin, et al., 1984]:

'* + ty*
" 3__ (27.11)

P B
and