Geological models, heterogeneities and scale relations

Geological models,
heterogeneities and
scale relations
Peter Frykman
Geologist & Geo-engineer
GEUS - Geological Survey of Denmark and Greenland
This is what you will hear
•
•
•
•
•
Motivation
Why do geological modelling?
How to do it?
What do we learn?
What is special for CO2 storage?
Tax deduction for solar panels
On June 1, 2005,
Governor Arnold Schwarzenegger signed
Executive Order # S-3-05,
greenhouse gas targets:
By 2010, Reduce to 2000 Emission Levels
By 2020, Reduce to 1990 Emission Levels
By 2050, Reduce to 80 percent Below 1990 Levels
BUT, hydrogen has different
colours!
His hydrogen converted Hummer
Sept 2009
• “We're investing billions to
capture carbon pollution so
that we can clean up our coal
plants “
Why modelling?
• It is the only way to ensure the public,
regulators and politicians about safety
– Predictions for the future
– Estimate capacity
– Quantify probability for events and risks
Important?
modelling
How?
• Model properties
– Size
– Geometry
– Scale
• Flow and reaction processes
-> other presentations this week
How to build a model
• Building blocks (cells in grid) assigned a
property – e.g. porosity or permeability
Decisions on model characteristics
•
•
•
•
How large gridblocks
Size of model
Computing capability
What is the question for the modelling
Model building
• Saline aquifers for storage often have very
few data at initial stage
• We need methods to populate the whole
model with properties
– Deterministic (hand-drawing)
– Interpolation
– Geostatistical modelling (random+rules)
• Object models
• Voxel models
Terminology
• A geological model can be a qualitative
characterisation – “Fluvial setting
developing into estuarine and shallow
marine”
• But it can also be a numerical model of
the facies geometry and their properties,
which can be used for flow calculations
and other calculations
Geological model –
Fluvial environment
with sand deposits
Numerical model –
Fluvial facies geometry
ready for flow simulation
How to use geology in modelling
Example:
• Regional model = Flood plain with river deposits
• Core description: sand, crossbedded, and nonmarine mudstone
• Environment = Fluvial
• Geometry = Channel belts with river deposits of
sandy pointbar systems and channel fills
• Translate that geometry into a numerical model
and add some properties
Input
Scandinavian highlands
Regional conceptual model
Floodplain with incised valleys
With fluvial deposits
Berlin
Marine influx
Input for channel belt simulation
Channel belts, not the individual river channel,
used as objects in model
100 - 1600 m width
Thickness = 1 - 8 m
Channel belt param.
Well data
and N/G sand
3500
BM_a
BM_b
fluvsim_orig
Robinson & McCabe 1997
12.1 1.9
Channel Belt Width
3000
2500
2000
1500
1000
500
0
0.0
2.0
4.0
6.0
8.0
Pointbar thickness m
10.0
12.0
Pointbar deposits
http://frg.leeds.ac.uk/
http://frg.leeds.ac.uk/
Heterogeneities!
Sand
Floodplain clay and silt
Crevasse splay
Pointbar top
5m
Sand
Sand
Triassic fluvial channel margin
Floodplain
Sand
Point-bar
Amalgamation
Sand
Shallow seismics of reservoir sands
V. Kolla, H.W. Posamentier and L.J. Wood, (2007), Deep-water and fluvial sinuous channels characteristics, similarities and dissimilarities, and modes of formation, Marine and Petroleum Geology
Deep-water example of meandering channel
Simple solution:
Low-sinuosity channel geometry ~ Channel belts
Anisotropic patchy permeability with SGSIM ~ Pointbars
mapview
5 km
3D model of fluvial system
1 layer
Porosity
Permeability
Model upscaling
• We like to model details to reflect the
small-scale variations so that it looks
realistic to the geologist
• BUT – too many gridcells for efficient
computations
• Upscaling!
From 48 to 6 blocks
• Upscaling by averaging is common
• Looks simple, but is usually more
complicated
– E.g. directional permeability etc
Permeability model upscaled into flow model
grid, having non-uniform grid
Kx in top layer of model
2
3
4
Claudia Schiffer
2
There
are
models
everywhere
3
4
Carla Bruni-Sarkozy
Models look great at a distance, but
they are never perfect
• It is too easy to make models!
Not symmetric
Excess pore space
Wrinkles
Challenge for the modeller
• How to best represent the most influential geological
features in a model,
• A model that can be used for flow simulation and
prediction of CO2 injection & movement,
• and can be used to evaluate site performance
(capacity, injectivity, risk studies)
•
•
•
•
Reservoir
Caprock
Faults
(Wells)
Site Model
components
+ for Earth Model:
• Overburden
What else?
• Site model looks OK “at a distance”, but
what have we missed?
10 m – 100 scale
Site model
Region scale
Meter scale
120x190 km region model
Small scale processes
Filling efficiency and
Capillary trapping
Small-scale effects due to
sub-meter scale heterogeneities
Flow simulation:
1) Fill with CO2
2) Let aquifer move in from below
3) Notice the above-endpoint
residual saturations in the sand
compartments
Well known from oil/gas that
finescale structure down to mm
and cm scale has en effect on
the displacement of fluids.
This could also be the case for
CO2 /water system, but not
fully studied yet
Reservoir rock at very small scale:
This is what we rely on – pore space
Large-scale interaction
• The pressure front travels much faster and
further than the actual flow
• With a site model of 12x16 km we must be
aware that the overpressure extends far into the
region around the site
• The extent and magnitude are influenced by
lateral connectivity (facies geometry, faults),
vertical communication (seals and caprock), and
compressibility of fluids and rock
Region scale
120x190 km region model,
pressure propagation during injection
When simulating industrial scale rates, the pressure
effect reaches outside the site model
Back to the site model
• Given that we can account for both the smallscale and the large-scale interactions, we can
now asses how our site behaves
• The interplay between geological structure
and the site behaviour
Sleipner
Utsira Fm.
GR log
North Denmark region with interfingering of facies:
Nearshore sandy sediments with continuous marine
mudstones as intraformational seals
S
E
F
Danish storage formation: Reservoir section at 1700-2100 m depth
Sedimentary facies
Shoreface
Marine mud
Sleipner
GR log
Shoreface
Estuary
Fluvial
350 m section
Sleipner
125 m thick
Homogeneous sand with
scattered thin clay layers
Typical Danish site
250 m thick
sand layers and
intraformational seals
of mudstone
CO2 distributed in layers
CO2 goes to top layer
Geology matters!
• Geology has consequences: different
geological models - different CO2
distribution
• Other presentations this week will deal
with flow, pressure, geochemical or
geomechanical effects.
• So, next 3 days – keep an eye on the
geology input and model assumptions
What is new for CO2 site
modelling compared to oil/gas
•
•
•
•
•
•
•
Few data to start with in saline aquifers
Longer time perspective for predictions
Pressure rise from injection
Mobility and gravity override
Trapping mechanisms
Close symbiosis with monitoring activities
(Geochemical reactions and
geomechanics)
Future challenges
• Improve the translation of geology into
numerical models
• Co-modelling involving different scales
• Management and description of
uncertainty
• Adjustments of model to a range of
different monitoring data
Conclusions
•Confidence: we have modelling tools that
work well
•Clarity: we need to state assumptions for
input and uncertainty for output
•Site specific modelling: is the only way to
assess performance and assure safety of the
operation