Carbon Sequestration
in Sedimentary Basins
Module II: Physical Processes
in C Sequestration…
Maurice Dusseault
Department of Earth Sciences
University of Waterloo
Geological Sequestration of C
C Sequestration
As CO2
An enhanced oil or gas recovery agent
Displacing formation water in deep aquifers
Storage in caverns (salt or rock caverns…)
As solid C
Injection of petcoke, coal wastes, etc
Biosolids injection and biodegradation to C
As a mineral precipitate
We will not consider this (unlikely) option
Geological Sequestration of C
Value-Added Options?
No value-added
Direct storage, no other “resource” is
accessed or extracted
This is only feasible in an incentive regime
that favors sequestration or places an
explicit value on C (e.g. tax or credit)
Value-added sequestration
C or CO2 used to access resources, is a
byproduct of an valuable process, …
Sequestration is a +ve but secondary factor
Geological Sequestration of C
CCS – CO2 Capture & Seques.
CO2 is captured
from some source
Or, flue gas is used,
(partly enriched?)
It is injected into
the ground, into
suitable porous and Typical Issues:
permeable media -Capacity and rate
The CO2 stays there -Value-added process?
-Economics
indefinitely
-Long-term fate
-… …
Geological Sequestration of C
+C-rich coal
waste injection
Geological Sequestration of C Alberta Research Council
HC Enhanced Recovery with CO2
Enhanced Oil Recovery – EOR
Enhanced Natural Gas Recovery – EGR
Enh. Coalbed Methane Recovery - ECBM
In each of these cases…
HC exists in a fluid or accessible form…
Conventional methods of production leave
significant % behind
CO2 can improve the recovery factor
CO2 largely left behind – i.e.: sequestered
Geological Sequestration of C
CO2 - EOR
Production
Well
CO2 Injection Recycled CO2
Other permeable and
non-permeable strata
Cap-rock or seal
CO2 OIL Reservoir
Δp
Geological Sequestration of C
Oil Production Phases…
Oil Rate
Phase I: Primary Depletion – Δp
Phase II: Water Flood, Δp-maintenance
Phase III: CO2 miscible injection
I
II
III
Time
Geological Sequestration of C
Why Different Phases?
History – CO2-EOR relatively new (1972)
Economics
Primary energy is the cheapest method
Waterflood, often re-injection of produced
H2O, is not as cheap, but still not costly
CO2 is relatively expensive, in comparison
Recovery Factors - RF
Primary RF from 20-40% (average ~)
Waterflood takes RF up to 30 to 70%
Miscible CO2 can take RF up to 70-90%
Geological Sequestration of C
Potential for CO2 in EOR
World-wide, perhaps 100×109 m3 oil
could be recovered with CO2-EOR in a
supercritical or liquid state
To recover 1 m3 of oil, likely we will have
to place from 0.5 to 2 m3 of SC-CO2, ρ ~
0.80, into the reservoir permanently
Mass sequestered =
100×109 m3 · 0.80 t/m3 · 0.5 = 40 Gt
Other assumptions, other figures…
Geological Sequestration of C
Exploring Some Possibilities…
Oil reservoirs suitable for CO2 found at
depths from 400 to 6000 metres
Shallower – risks of escape too high
Deeper – no oil, very expensive, etc.
Now, we have to understand several
factors:
How does CO2 behave?
Technical options for oil recovery?
Does CO2 injection fit in with these?
Geological Sequestration of C
CO2 Behavior
We must understand the behavior
of CO2 and the site conditions!
Geological Sequestration of C
Pure CO2 Behavior
Gaseous state
Low density, low viscosity, under low p, T
Liquid state
High density, low μ, high p, low T 35ºC, > 7.2 MPa
(> 95ºF, > 1035 psi, approximately)
High ρ, low μ,
Fully miscible with water and oil
Hydrate formation – low T, high p, +H2O
Geological Sequestration of C
Depth and CO2 State - I…
20 40 60
0 0
T increases w. depth
~20-25ºC/km T - ºC
In most areas, T > TSC
35ºC below ~800 m
In cold conditions,
pure CO2 will be in a
1000
a liquid state
In the presence of
water and high p, a Typical range
CO2-H2O clathrate 2000
of T with depth
(hydrate) forms Depth below
ground - m
Geological Sequestration of C
Depth and CO2 State - II…
20 40 60
Most reservoirs to Z 0 0
= 3 km: hydrostatic gas
T - ºC
pressures ~10 kPa/m TSC
gas
Pure CO2 is SC below pSC
~750 m, if T > 35ºC liquid
In general, CO2 is a
1000
liquid
supercritical fluid at
Z > 800 m (~2620’) SC-CO2
Otherwise, it is a
gas or a liquid, 2000
depending on p & T Depth below
ground - m
Geological Sequestration of C
Gaseous CO2 Use in Recovery
Geological Sequestration of C
Technologies for CO2 use
Displace CH4 from coal seams
Deeper seams could be depressurized so
pinj gog + gwo
oil
Recovery % can be high
Geological Sequestration of C
IGI, With Reservoir Structure
inert gas injection
gas rates are controlled to
avoid gas (or water) coning mainly
gas
three-phase zone
horizontal wells
parallel to structure
oil bank, two-phase zone
Dr
water-wet sand
water,
Dp
one phase best to monitor
the process;
if coning develops,
drop pressures!
Geological Sequestration of C
Miscibility of Oil and CO2
68 bar – 1000 psi 102 bar – 1500 psi 170 bar – 2500 psi
Immiscible CO2 Miscibility begins to develope CO2 has developed miscibility
Final stage: Higher HC forms Higher hydrocarbons (dark spots)
continuous phase- CO2 immiscible begins to condense
Geological Sequestration of C
Physical Properties…
Porosity - φ -
controls storage φ
Void space
volume available: (fluids)
φ = fractional void
space of the rock
V of solid
1-φ mineral
Geological Sequestration of C
Physical Properties…
Permeability is the ability to transmit
fluid (gas or liquid or SC-fluid)
•L = 40 – 100 mm
•In the field, “L” =
100 – 2000 m L
Δp
A
Geological Sequestration of C
Fluids - Oil, H2O, Gas, CO2 …
Viscosity = ƒ(T…), Salinity (of H2O)
Solubility behavior (diffusivity, mixing,
h, contact area…)
Density = ƒ(p, T…), i.e.: p-V-T behavior
(EOS) (API gravity, Compressibility…)
Miscibility-pressure relationships in CO2
Surface tensions
Asphaltene%, Other oil characteristics
And so on…
Geological Sequestration of C
Reservoir Conditions
Pressure (in the fluids)
Temperature
Stress (solid rock matrix)
Current bubble point pressure of liquids
Gas-to-oil ratio in situ
Saturations: So, Sw, Sg
Production history, well test data…
Geological Sequestration of C
Reservoir Simulation
A reservoir model is put together (see
Module III for how this is done)
The physics are incorporated as well as
we can
PVT laws, dissolution kinetics, multiphase
fluid flow, hydrate formation…
Supercritical conditions
Contaminating gases
Calibration, if possible, then predictions
Geological Sequestration of C
Gaseous CO2 Distribution
Geological Sequestration of C
Dissolved CO2 Distribution
Geological Sequestration of C
Leakage Mechanisms
Flow through intact pore structure in
shale or anhydrite cap rocks is slow
The main concerns appear to be…
Flow along an anthropogenic path, old or
new wells, perhaps improperly sealed
Flow through natural fracture systems
Flow along a faulted structure
Geological Sequestration of C
Interfacial Tensions
In the immiscible state, the CO2 that
remains undissolved has a surface
tension with water ƒ(p, T, salinity…)
With SC-CO2, no surface tension
(mutually miscible)
Similarly with light oils
The situation with heavy oils is more
complicated because of asphaltenes…
However, this means that capillarity as
a flow barrier almost disappears!
Geological Sequestration of C
CO2 Behavior…
Extremely complex…
Oil swelling with CO2 adsorption
Interfacial tension issues (changes as a
function of p, T, oil chemistry…)
Diffusion rates into H2O, oil…
Phase relationships in mixtures of
gases, liquids (e.g SC-CO2 + oil + H2O), …
Changes in rock wettability…
Formation of hydrate phases…
Geological Sequestration of C
Pure CO2 Phase Behavior
Geological Sequestration of C
p-T-ρ EOS
Weyburn conditions – ~15 MPa, ~45ºC
Geological Sequestration of C