Uncertainty in reservoirs
1 - Classification: Internal
2010-05-27
Deepwater Horizon – Gulf of Mexico
The slightly more mundane situation I consider:
–We have a hydrocarbon reservoir
–We have a model for the reservoir which will be used for future decisions.
–The parameters in the model are uncertain.
What do we do with the uncertainty?
Operational uncertainties are unfortunately not a topic in this presentation.
2 - Classification: Internal
2010-05-27
Uncertainty in the petroleum industry
Organisational issues:
– Strong financial inertia to ”stick with the truth”.
– Tradition for compartmentalized organisations where uncertainty information
is not passed on.
– ”What happens happens” – limited tradition to reevaluate uncertainty
estimates.
Current topics:
– Choice of parameters – model selection.
– Different scales.
– Stochastic modelling.
3 - Classification: Internal
2010-05-27
$€£ $€£ $€£
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Maybe the reservoir
is larger?
Producing fields:
Or smaller?
There is so much money, financial regulations e.t.c. in these questions that there is a
strong organisational urge to just ignore the uncertainty.
4 - Classification: Internal
2010-05-27
An organisational challenge
Structural model
OK; I pass my
best result on to
Deborah!
5 - Classification: Internal
2010-05-27
I am working hard to
interpret the seismic
and build a structural
model.
Geological model
I am doing flow
simulations, and
I pass my best
management
even wants
I am creating
a
Welluncertainty
- I’ll try outestimates these
effort on to geological
different values for
a
Phillip.
days
model.
couple of parameters
and see what happens.
”What happens happens”
1. We do our best to model and quantify uncertainty.
2. We make a decision to e.g. drill a well:
– Estimated oil volume: A +/- B – found nothing!
– Estimated gas volume: A +/ B – found both gas and oil.
3. The new information is used to infer that we were just wrong. Uncertainty
estimates are not really challenged.
6 - Classification: Internal
2010-05-27
History matching – it is just plain stupid
Traditionally History Matching is percieved as an optimization problem – a very
problematic approach:
–The problem is highly nonlinear, and severely underdetermined.
–The observations we are comparing with can be highly uncertain.
–The choice of parameterization is somewhat arbitrary – we will optimize in the
wrong space anyway.
7 - Classification: Internal
2010-05-27
Geological concept
Channel system
Deep marine
The choice of geological
concept
is an example of a choice which will have a
Shallow
marine
profound effect on subsequent interpretations, and decisions.
8 - Classification: Internal
2010-05-27
Good agreement between model
simulation and observation!
Model/parameter selection II
Two wrongs do not make a right – it is all to easy to get ”a match” for the wrong
Maybe
the ”real” reason was that the
reasons:
oil-water interface was shallower?
Water rate
Oil
Water
Time
–Simulations show to little water.
–Increase relative permeability of water
9 - Classification: Internal
2010-05-27
Different scales
4
Geo object
2
5
1
~50 m
~0.25 m
10 - Classification: Internal
2010-05-27
~10 m
3
Different scales II
Pores
Reservoir
~ 9 orders of magnitude
11 - Classification: Internal
2010-05-27
Different scales III: Upscaling
1
Permeability: 1<< 2<<3
1
Vertically:
T

1
1

1
2

1
3

2
1
1
3
T  1   2   3   3
Horisontally:
1
2
3
12 - Classification: Internal
2010-05-27
~3
~ 1
Different porosity realisations
Geostatistics
It is quite common to sample properties like
permeability and porosity stochastically –
with various constraints/trend parameters:
Spatial gradient
Point measurements
Correlation
length
13 - Classification: Internal
2010-05-27
Modelling – the full loop
Sample geostatistical parameters
Ideal approach:
Sample a geological realisation
according to the parameters.
Perform flow simulations and
evaluate misfit.
14 - Classification: Internal
2010-05-27
Make all alterations
Traditional
approach: on geo
parameters, and keep everything
1.syncronized.
Cutting the link to geostatistical
paramaters.
2. Direct updates of the properties of the
realisation
McMC and stochastic modelling – attempt 0
The geo modelling process is not a closed form PDF; it can only be observed from the
created realizations.
We have tried to update update geo parameters; initial attempts show some success!
Uncertainty:
Cdd  C0  CC  CS
15 - Classification: Internal
2010-05-27
Example – channel direction
Oo
Prior: θ~100
Posterior:
θ~0
Conditioning the distribution
P(θ|d) with McMC
16 - Classification: Internal
2010-05-27
Main challenges
1. Model selection – and how to handle the ”Uknown unknowns”.
2. Conditioning of coarse parameters like geostatistical trends.
Thank you!
17 - Classification: Internal
2010-05-27