Geoscience Reference
In-Depth Information
variability and low variability (the REV) -
similar to Fig.
4.21
- using the sketch below.
Note that the horizontal axis is given as
a vertical length scale (dz, across bedding)
to make volume estimation easier.
Exercise 4.2
Find the REVs for your reservoir?
Use your own knowledge a particular
geological reservoir system or outcrop to
sketch on the most likely scales of high
Scales of measurement
1000
Lithofacies
scale
Geological Sequence
scale
Pore/lamina
scale
100
10
1
0.0001
0.001
0.01
0.1
1
10
100
Vertical Lengthscale [m]
4.3.5 Construction of Geomodel
and Simulator Grids
adequate 3D grids for realistic fault architectures,
and significant manual work is necessary.
Upscaling procedures for regular Cartesian
grids are well established, but the same operation
in realistically complex grids is much more
challenging.
The construction of 3D grids suitable for res-
ervoir simulation is also non-trivial and requires
significant manual editing. There are several
reasons for this:
• The grid resolution in the geologic model and
the simulation models are different, leading to
missing cells or miss fitting cells in the simu-
lation model. The consequences are overesti-
mation of pore volumes, possibly wrong
communication across faults, and difficult
numerical calculations due to a number
small or “artificial” grid cells.
• The handling of Y-shaped faults using corner
point grid geometries (now widely used in
black oil simulators) is difficult. Similarly,
the use of vertically stair-stepped faults
The choice of grid and grid-cell dimensions is
clearly important. Upscaled permeability, the
balance of fluid forces, and reservoir property
variance are all intimately connected with the
model length-scale. The construction of three
dimensional geological models from seismic
and well data remains a relatively time consum-
ing task requiring considerable manual work
both in construction of the structural framework
and, not least, in construction of the grid for
property modelling (Fig.
4.27
).
Problems especially arise due to complex
fault block geometries including reverse faults
and Y-faults (Y-shaped intersections in the verti-
cal plane). Difficulties relate partly to the
mapping of horizons into the fault planes for
construction of consistent fault throws across
faults. Currently, most commercial gridding soft-
ware is not capable of automatically producing
