Geoscience Reference
In-Depth Information
The next question is which petrophysical
properties do we want to model? The focus in
this chapter will be on modelling porosity (
Exercise 3.1
Which methods to use?
Think through the following decision
matrix for an oilfield development to
decide which approaches are appropriate
for which decisions?
)
and permeability (k) as these are the essential
parameters in the flow equation (Darcy's law).
The methods discussed here for handling
ϕ
and k
can also be applied to other properties, such as
formation bulk density (
ϕ
ˁ
b
) or sonic p-wave
velocity (v
p
), Volume fraction of shale (V
shale
)
or fracture density (F
d
), to name but a few.
Table
3.1
lists the most commonly modelled
rock properties, but the choice should not be
limited to these, and indeed a key element of
the design should be careful consideration of
which properties should or can be usefully
represented. Integration of dynamic data with
seismic and well data will generally require
modelling of several petrophysical properties
and their cross correlations.
Permeability is generally the most chal-
lenging property to define because it is highly
variable in nature and is a tensor property depen-
dent on flow boundary conditions. Permeability
is also,
Method (for a
given reservoir
interval)
Choice
Purpose
Conceptual
geological sketch
of proposed
reservoir analogue
Initial fluids-in-
place volume
estimate
Simple average
of porosity,
ϕ
,
permeability, k,
and fluid
saturation, S
w
Preliminary
reserves estimates
2D map of
ϕ
,k
Reserve estimates
for designing top-
side facilities
(number of wells,
platform type)
and S
w
(e.g.
interpolation or
kriging between
wells)
3D model of
ϕ
,k
Definition of
appraisal well
drilling plan
and S
w
in the
reservoir unit
(from well data)
in general, a non-additive property,
that is:
3D model of
ϕ
,k
and S
w
for each of
several model
elements (from
well data)
Definition of infill
or development
well drilling plan
X
n
k
ʔ
V
k
∂
v
i
6
¼
ð
3
:
1
Þ
1
In contrast porosity is essentially an additive
property:
3D model of
ϕ
,k
Submitting
detailed well
design for final
approval
and S
w
conditioned to
seismic inversion
cube (seismic
facies)
X
n
1
ϕ
∂
v
ϕ
ʔV
¼
ð
3
:
2
Þ
i
ʔ
ʴ
where
v[n] is the
exhaustive set of small scale volumes filling the
large-scale volume.
Put in practical terms, if you have defined
all the cell porosity values in your reservoir
model then the total reservoir porosity is pre-
cisely equal to the sum of the cell porosities
divided by the number cells (i.e. the average),
whereas for permeability this is not the case.
We will discuss appropriate use of various
permeability averages in following section.
V is a large scale volume,
3D model of
ϕ
,k,
Designing
improved oil
recovery (IOR)
strategy and
additional well
targets
S
w
and facies
conditioned to
dynamic data
(production
pressures and flow
rates)
3D model of
ϕ
,k,
S
w
and facies
integrating multi-
scale static and
dynamic data
Implementing
enhanced oil
recovery (EOR)
strategy using an
injection blend
(e.g. water
alternating gas)
