Geological Sequestration of C
Carbon SequestrationCarbon Sequestrationin Sedimentary Basinsin Sedimentary Basins
Module V: Carbon Dioxide Module V: Carbon Dioxide Storage in Salt CavernsStorage in Salt Caverns
Maurice DusseaultDepartment of Earth Sciences
University of Waterloo
Geological Sequestration of C
Why Salt Caverns for COWhy Salt Caverns for CO22??
In areas where other options limited In areas with suitable salt deposits Near point sources of CO2
Heavy oil upgrading facilities, cement Coal-fired power plants, gasification Steel manufacture, petrochemical plants
Caverns can pay for themselves NaCl brine has value Facilities’ CAPEX can be amortized
Geological Sequestration of C
Cavern Design Cavern Design
Integrity Stability Security Safety Longevity … …
approximatecavernshape
overburden
roof salt, >25 mcasing shoe
limestone, shale
shale, anhydrite
salt
rubble floor salt, >10 m
15 m
roof span
D ~ 100 mbounding ellipsoid
internal pressure pi
z - depth
H ~ 75-100 m
Geological Sequestration of C
Caverns: Temporary Caverns: Temporary Storage…Storage… Salt cavern integrity is difficult to
guarantee in perpetuity Hence, salt caverns with supercritical
CO2 are considered temporary storage Seasonal (12-month cycle, several years),
in order to smooth transshipment needs Generational (20-100 years), to store
excess CO2 until disposal or use is possible Long-term (50-500 yrs), but likely not
longer because of uncertainty
Geological Sequestration of C
A Typical Case History:A Typical Case History:The Lotsberg Salt:The Lotsberg Salt:
Location and GeologyLocation and Geology
Geological Sequestration of C
Geological Environment
Western Canadian Sedimentary Basin
Tectonically stable
Thick, pure salt deposits>95% NaCl in Lotsberg
3 salt zones (security)
Overlying competent rock
Close to CO2 point sources
Geological Sequestration of C
WHERE?WHERE?
Saskatchew
an
Alberta
Calgary
Prairie FormationSalt Deposit
LOTSBERGSALT
Edmonton
Athabasca Oil Sands
Cold Lake Oil Sands
Wabiskaw Deposits
Heavy Oil Belt
Major CO2 Point Sources Synthetic crude and Petrochemical sites
Coal-fired power sites
Geological Sequestration of C
Lithostratigraphy
Overburden strata
Prairie Salt, excellent flow barrier
Dolomites and shales, one aquifer
Cold Lake Salt, excellent barrier
Low-k roof beam Ernestina Lk Fmn
Lotsberg Salt – 160 m of pure salt
Underburden, dense silts, shales
Geological Sequestration of C
Analysis and Some Analysis and Some ResultsResults
Geological Sequestration of C
Approach to pApproach to pcct Analysist Analysis
Numerical models are inaccurate Numerical dispersion for long times Local discretization leads to errors
New semi-analytical model developed Viscoelastic salt behavior, n = 3 Coupled to Peng-Robinson EOS
Idealized spherical or ellipsoidal shape Infinite salt half-space
Geological Sequestration of C
Salt Deformation BehaviorSalt Deformation Behavior
Time
Str
ain Increasing shear stress (~ - pc) = faster creep
Transient creep only for the first few weeks
Steady-state creep after a few weeks of a p
Extremely slow creep rates when cavern pressure approaches the regional stress
Geological Sequestration of C
Steady-State Creep LawSteady-State Creep Law
ss = steady-state creep rate = initial stress in salt pc = pressure in the CO2 in cavern A, o = material-dependent constants n = creep law exponent
The critical parameter in creep predictions = 3.0, based on mine back-calculations Also, from data on long-term lab creep tests
n
o
css
pA
Geological Sequestration of C
Equation of State for COEquation of State for CO22
For analysis, we coupled cavern closure behavior to CO2 compressi-bility using the Peng-Robinson EOS
Experimental phase behavior data for pure CO2
Geological Sequestration of C
ppcc t for Cavern Closure t for Cavern Closure1.0
0.8
0.6
0.4
0.2
01000 2000 3000 4000
Time in years
No
rmal
ized
ca
vern
pre
ssu
re1.0
0.8
0.6
0.4
0.2
01000 2000 3000 4000
pc1.0v
pc0.5 v
Geological Sequestration of C
Cavern Pressure ResponseCavern Pressure Response
CO2 is always in a supercritical state Salt exhibits slow creep closure Slow closure gradually pressurizes
CO2
Long-term pressure response is only weakly sensitive to filling pressure
In ~4000 years, pc ~ 94% of v
Final density approaches 0.92 g/cm3
Geological Sequestration of C
Subsidence at the Subsidence at the Surface?Surface?
Z ~
120
0 m
100 m diameter
Greatest subsidence will be right above the cavern for the case of a single cavern
Subsidence will decay to negligible values at distances greater than 5Z from the cavern location
For an array of caverns, the subsidence depends on how many caverns, at what spacings, & the V/t
spacing
Geological Sequestration of C
Subsidence ResponseSubsidence Response For the following case:
Single 100 m Ø cavern, Vi ~ 500,000 m3
Filled to 14 MPa (pressure of a brine column to the surface)
Cavern sealed in perpetuity Volume change in cavern ~ 78,000
m3
2.5 mm displacement in first 150 yrs 2.5 mm thereafter (as t )
Geological Sequestration of C
Sequestration Security Sequestration Security IssuesIssues
Geological Sequestration of C
Leakage MechanismsLeakage Mechanisms
low permeability
high permeability
brines, = 1.2salt
fresh water, = 1.0
fracture
p advection
wellbore
wellbore leakage
permeable interbeds
Geological Sequestration of C
Security?Security?0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
De
pth
in M
etr
es
Glacial and Recent strata
Cretaceous and Tertiary sands, silts and shales.
Karstic erosion surface
Devonian carbonate strata
Prairie Evaporites,
Keg River, Chinchaga Fmns.Cold Lake FormationErnestina Lake Fmn
Lotsberg Salt
Basal Red Beds
Igneous, metamorphic rocks
Ductile shales (kv ~ 0)
Flat-lying strata
No faults, folds
Massive salts (kv = kh ~ 0)
Geological Sequestration of C
Regional Storage SecurityRegional Storage Security Regionally ~ flat-lying strata Three integral massive salt seals
Permeability to gas = 0 Great lateral extent (100s of km)
No faults or folds Ductile shales, depths of 200-400 m Water-filled porous strata
CO2 can go into solution if it escapes
Geological Sequestration of C
Secure Cavern Secure Cavern DesignDesign
Overlying salt beds
Non-shrinking, ductile cement
Special squeezed cement seals
Salt-occluded porosity in bounding strata
25-35 m overlying salt barrier
90-100 m high “spherical” cavern
Thick lateral salt beds
15-20 m lower salt barrier
Salt-occluded porosity in Red Beds
Geological Sequestration of C
Cavern-Scale SecurityCavern-Scale Security
Proper site location Salt barriers (30-40 m overlying) Occluded porosity in adjacent strata
Salt infills the porosity in bounding beds ~Spherical shape (max ellipticity
1.5) Ductile non-shrinking casing cement Installation of high pressure
squeezed cement plugs Etc
Geological Sequestration of C
CONCLUSIONSCONCLUSIONS The Lotsberg Salt is an exceptionally
favorable deposit for CO2 storage The regional geology also is favorable Two caverns (~106 m3) could take Al-
berta point CO2 emissions for 5 years Analysis shows that >4000 years are
needed for pressure 95% of v
Filling and sealing are relatively straightforward technically
Geological Sequestration of C
Some Predictions…Some Predictions…
Generally available competitive H2 fuel cell cars at least 20 years away
Biosolids injection will be a huge industry in 30-40 years
Separation, deep injection of gaseous, supercritical CO2 may happen…(?)
Nuclear energy is poised for a major comeback (no CO2!)
Taxes are going to go up
