Storage 1- Reservoirs, Traps, Seals and

Storage Capacity for CO2 Storage

Professor John Kaldi

Chief Scientist, CO2CRC
Australian School of Petroleum,
University of Adelaide, Australia

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Geological storage of carbon dioxide
(a simple solution)

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 Geological
Carbon captureStorage of Carbon
& storage Dioxide
(CCS) value chain

Greatest uncertainty!

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 Summary

Greatest
uncertainty!

Reducing the uncertainty with geological storage of CO2 requires exploration and
site specific studies including reservoir characterisation to understand storage
capacity, injectivity and containment. Technologies required include geophysics,
geochemistry, geomechanics, modelling, monitoring, economics and risk analysis…
technologies used commonly by the petroleum industry and being
developed for CCS through demonstration projects
- learning by doing!

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Geological storage of CO2
What do we need?
RESERVOIR ROCK – porous,
e.g. sandstone

SEAL ROCK – non-porous,

Claystone e.g. claystone
seal rock
Occurring at appropriate depth

Sandstone
reservoir rock

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 IEAGHG CCS Summer School
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 Geological Structures

“Ductile” deformation results in FOLDS.

Convex upwards folds are called ANTICLINES.

Concave upwards folds are called SYNCLINES.

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 Geological Structures: Anticlines & Synclines

Anticline – syncline; Calico, Mojave, CA

Anticline, road cut, near

Oak Ridge, Tennessee

IEAGHG CCS Summer School https://en.wikipedia.org/wiki/Calico,

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_San_Bernardino_County,_California 8
Structural trap for CO2: AnticlineTrap

• Injection into reservoir rock

• Buoyancy drives CO2 upwards

• Top seal prevents escape

• Such features have safely held

oil, gas & natural accumulations
Seal of CO2 for millions of years

Anticline

Reservoir

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 Geological Structures: Faults
“Brittle” deformation results in Faults and/or Fractures

Faults and fractures are breaks (cracks) in the rocks that make up the
Earth’s crust that have formed as a response to natural or induced
stresses

A fault is where rocks on either side of the crack have moved past each
other; a fracture is where there has been no motion.

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 Geological Structures: Faults
>L
FAULTS form due to earth stresses
Extension results in NORMAL
faults.

L <L

Compression results in REVERSE

or THRUST faults.

L
Horizontal shearing results in
STRIKE SLIP or WRENCH faults.

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 What sort of fault is this?

Normal Fault, near Moab, Utah

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 What sort of fault is this?

Reverse (thrust) fault, Ketobe Knob, Utah

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What sort of fault is seen on this air photo?

Strike-slip fault, San Andreas, California

Small offset fault on hwy 18, North Park, CA
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Structural trap for CO2: Fault Trap

• Injection into reservoir rock

• Buoyancy drives CO2 upwards
• CO2 retained by:
– Fault juxtaposed seal-on-
reservoir
– Shale gouge / cement on
fault plane
Risks: fault reactivation
− ∆ P (from injection)
– natural seismic events

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 Stratigraphic trapping

Unconformity Pinch out

Stratigraphic traps are created by changes in rock type. These traps

have historically been regarded as high risk, because identification
of rock type is much less certain on seismic data than delineation of
structure.

Examples are: UNCONFORMITY traps.

PINCHOUT traps.

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What sort of feature is this?

Unconformity, near Moab, Utah

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CO2 Storage Trapping Mechanisms

Structural /
Stratigraphic
Trapping
(SST)

Most familiar; best

understood;
lowest risk

From IPCC SRCCS, 2005

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Storage in Deep Saline Formations

Sample only

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CO2 Storage Trapping Mechanisms

Migration
Associated
Trapping
(MAT)

• Least familiar
• modelled, but poorly
understood
• highest uncertainty
• focus of many
storage demo projects
From IPCC SRCCS, 2005

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 CO2 storage effectiveness increases with time

(Modelling the dissolution of injected CO2)

•Homogeneous Reservoir
•Flat-lying Seal
1yr •Cross-sectional view

5 yr

30 yr
From: J. Ennis-King

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 CO2 storage effectiveness increases with time

(Modelling the dissolution of injected CO2)

40 yr

130 yr

330 yr

From: J. Ennis-King

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 CO2 storage effectiveness increases with time

(Modelling the dissolution of injected CO2)

930 yr

1330 yr

2330 yr
From: J. Ennis-King

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 Mineral trapping: also increases with time
Calcite cement (red)

1m
1 mm

1 cm
CaCO3 (Calcite) precipitation occurs at all
scales at different rates 200 µm

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RESIDUAL CO2 SATURATION BY PLUME MIGRATION

Residual CO2

CO2

“Snap-off”
Grain

H2O

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 Residual CO2 saturation during plume migration
(CAPILLARY TRAPPING)

Water filled
pore Residual
(trapped) CO2

CO2 enters pore

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CO2 storage effectiveness increases with depth

“Dense-phase”
Supercritical CO2:
gas-like viscosity, liquid-like density

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 Containment of CO2

Caprock properties controlling containment

Fault properties controlling containment

Rate controls on containment

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 Caprock Properties: “Seal potential”

Capacity:
• maximum CO2 column that can be retained
by caprock

Geometry:
• thickness and lateral extent of the caprock

Integrity:
• geomechanical properties of caprock

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Evaluating seal capacity of caprocks for CO2
containment
Relative densities: Oil > CO2 > CH4
Relative buoyancy: Oil < CO2 < CH4

Seal
CH4
Relative retention
CO2 capacity (column
heights) for gas, oil
Oil and CO2 by same
seal and reservoir.
(non-dimensional)

Reservoir

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 Evaluating seal capacity of caprocks for CO2
containment

• If the seal capacity is calculated as being too low to hold

the required column, the cap rock may still be OK, because
low permeabilities may inhibit migration = “rate” seal
• If upward migration through the seal does occur, it would
be at very slow rates
• Calculated migration rates of CO2 through Muderong
Shale (NW Shelf, Australia) >0.3Ma / 100m for migration
- Muderong Shale = 1500 metres thick; Break-through
in 4.5 million years

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 Seal geometry
Refers to thickness and areal extent of caprocks
Estimated by integrating seismic, core & well log data, with
geological/depositional models

Static model
Seismic Core Well logs

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 Intraformational seals (baffles)
increase length of CO2 migration pathways & potential for Sgr and dissolution

1m

H. Johansen

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 Intraformational seals (baffles)
increase length of CO2 migration pathways & potential for Sgr and dissolution
CO2
injection 2km below sea
well bed
Lakes Entrance Formation

C. Gibson-Poole

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 The role of faults in CO2 containment
Faults and fractures are breaks (cracks) in the rocks that make up the
Earth’s crust that have formed as a response to natural or induced
stresses

A fault is where rocks on either side of the crack have moved past each
other.

Faults do not necessarily act as fluid conduits; empirical evidence that

many thousands of hydrocarbon accumulations are trapped by sealing
faults

In such cases, either the fault itself acts as a seal or the juxtaposition of
rocks across the fault results in sealing
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 Shale-sand juxtaposition traps CO2

CO2

Tectonic forces “juxtapose” sealing rocks against

reservoir rocks, on either side of a fault, resulting in
trapping of buoyant fluids (oil, gas, CO2)

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 Clay Smear (Shale Gouge)

Yielding et al 1997

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 The role of faults in CO2 containment

Faults and fractures are breaks (cracks) in the rocks that make up the
Earth’s crust that have formed as a response to natural or induced
stresses

A fault is where rocks on either side of the crack have moved past each
other.

Faults do not necessarily act as fluid conduits; empirical evidence that

many thousands of hydrocarbon accumulations are trapped by sealing
faults

In such cases, either the fault itself is acting as a seal or the

juxtaposition of rocks across the fault results in sealing

Fault movement (reactivation) could result in fluid migration along the

fault & potential leakage unintended migration

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Juxtaposition + Reactivation

CO2

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Juxtaposition + Reactivation

CO2

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Juxtaposition + Reactivation

CO2

Residual Saturation
(SgrCO2)

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 Seal Integrity: Geomechanics

The Stress Tensor:

• Key to understanding risk of induced seismicity
• By understanding the orientation of the in-situ stress
field, and any induced stress, relative to the orientation
of existing faults, we can predict the likelihood of
reactivation of those faults Sv

SHmax
Shmin
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 Storage Capacity
What do people want to know about storage capacity?

How much will go in?

• Volumetric approach –
current state of art

Hovorka, 2014
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 Storage Capacity

Risk / “Consequences” Approach to Capacity

How much will go in

before unacceptable
consequences
occur?

Hovorka, 2014
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 Storage Capacity

Largely controlled by
Injectivity

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Hovorka, 2014
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 Injectivity
Iv/t = A * Pi * k
Iv/t = Injection rate
A = Area (of wellbore in contact with formation)
Pi = injection pressure (below frac pressure)
k = permeability

(k, Pi are constant;

A is proportional
to number and
orientation of wells)

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 Injectivity / Pressure Considerations:
• Pore space in storage formations already full….injection of fluids (eg CO2)
causes reservoir pressure build up

• In depleted fields, pressure build-up may be beneficial or neutral

• In both depleted fields and saline aquifers, must maintain pressure below
fracture pressure

• In low permeability reservoirs this may limit economic storage capacity due
to decreased injection rate, requiring more wells

• Injection in saline formations may displace saline fluids & increase risk of
possible mixing with freshwater system

• Drilling pressure relief (water production) wells is a possible solution

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 Storage capacity estimation
Techno-Economic
Resource-Reserve
Pyramid for CO2 Storage
Capacity

Kaldi et al, 2008

Modified from Bachu et al., CSLF, 2005

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 Storage capacity estimation

Total Pore Volume

Contingent
Total physical limit of what Capacity
the storage
Subset of Operational
prospective Capacity
capacity obtained by
system can accept. Assumes
Prospective entire
Capacity volume
Subset of contingent capacity andobtained by
isconsidering
accessible
Subset of
technical,
to store
Total Pore CO legal
Volume
2 in the
and
regulatory,
pore spaceby
obtained
detailed matching
infrastructure of large,economic
stationary
or dissolved
applying in and general
formation
technical fluids&or
(geological
sources with geological storage sites that
barriers.
adsorbed at 100% onto
engineering) total coal volume.
are adequatelimits. This
in terms ofestimate
capacity,usually
This represents
changes with the maximum
acquisition upper limit
of Corresponds
new data or to
injectivity
Value prone and
to supply rate.
changes as technology, to
aknowledge
capacity estimate.
“Proved,
policy, marketable
regulations reserves”
and/or used by
economics
mining industry
change. Corresponds to “Reserves”
However, this is an unrealistic numberasas
used will
there in energy
alwaysand mining industries
be physical, technical,
regulatory and economic limitations.

Kaldi et al, 2008

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Volumetric equation for storage capacity calculation

GCO2 = A hg φ ρ E

GCO2 = Volumetric storage capacity

A = Area (Basin, Region, Site) being assessed
hg = Gross thickness of target saline formation defined by A
φ = Avg. porosity over thickness hg in area A
ρ = Density of CO2 at Pressure & Temperature of target saline formation
E = Storage “efficiency factor” (fraction of total pore volume filled by CO2)

NETL DOE, 2006

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 Storage capacity estimation
Techno-Economic
Resource-Reserve Pyramid
for CO2 Storage Capacity

xE

1 – 4%
Kaldi et al, 2008 (van der Meer and others)

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Questions?

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© CO2CRC 2015
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