Page 181 - Principles of Applied Reservoir Simulation 2E

166 Principles of Applied Reservoir Simulation

16.4 Basic Simulator Volumetrics

Reservoir simulators calculate reservoir volume using a procedure similar
to the procedure described in this section. Bulk volume V B of each gridblock
defined in a Cartesian coordinate system {x, y, z} is calculated from the gross
thickness Az = h of each gridblock and the gridblock lengths Ax, Ay along the
x andy axes:

Porosity <j) and net-to-gross ratio T) are then used to calculate gridblock pore
volume
V p = §r\V B = $T\hAxAy = §h nelAxAy
where net thickness is defined by h net = r\h. The volume of phase $ in the grid-
block at reservoir conditions is the product of the gridblock pore volume and
phase saturation, thus
V = SV , P

where S' ? is the saturation of phase 1 Total model volumes are calculated by
summing over all gridblocks.
Many commercial simulators provide optional variations on the simple
procedure outlined above. A comparison of reservoir simulator calculated volu-
metrics with volumetrics from another source, such as a material balance study
or a computer mapping package, provides a means of validating volumetric esti-
mates using independent sources.

Exercises

Exercise 16.1 Sketch the model grids for data sets EXAM 1 .DAT, EXAM2.DAT,
EXAM3.DAT, EXAM5.DAT, and EXAM7.DAT using information from each
data set,

Exercise 16.2 Repeat Exercise 16. 1 for case study data sets CS-MB.DAT, CS-
VC.DAT, and CS-XS.DAT.