Geological Sequestration of C Carbon Sequestration in Sedimentary Basins Module V: Carbon Dioxide Storage in Salt Caverns Maurice Dusseault Department of Earth Sciences University of Waterloo

Geological Sequestration of C Why Salt Caverns for CO 2 ?  In areas where other options limited  In areas with suitable salt deposits  Near point sources of CO 2  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  Integrity  Stability  Security  Safety  Longevity  … approximate cavern shape overburden roof salt, >25 m casing shoe limestone, shale shale, anhydrite salt rubble floor salt, >10 m 15 m roof span D ~ 100 m bounding ellipsoid internal pressure p i z - depth H ~ m

Geological Sequestration of C Caverns: Temporary Storage…  Salt cavern integrity is difficult to guarantee in perpetuity  Hence, salt caverns with supercritical CO 2 are considered temporary storage  Seasonal (12-month cycle, several years), in order to smooth transshipment needs  Generational ( years), to store excess CO 2 until disposal or use is possible  Long-term ( yrs), but likely not longer because of uncertainty

Geological Sequestration of C A Typical Case History: The Lotsberg Salt: Location 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 CO 2 point sources

Geological Sequestration of C WHERE? Saskatchewan Alberta Calgary Prairie Formation Salt Deposit LOTSBERG SALT Edmonton Athabasca Oil Sands Cold Lake Oil Sands Wabiskaw Deposits Heavy Oil Belt Major CO 2 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 Results

Geological Sequestration of C Approach to p c  t 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 Behavior Time Strain Increasing shear stress (~  - p c ) = 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 Law   ss = steady-state creep rate   = initial stress in salt  p c = pressure in the CO 2 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

Geological Sequestration of C Equation of State for CO 2 For analysis, we coupled cavern closure behavior to CO 2 compressi- bility using the Peng-Robinson EOS Experimental phase behavior data for pure CO 2

Geological Sequestration of C p c  t for Cavern Closure Time in years Normalized cavern pressure p c   1.0  v p c  0.5  v

Geological Sequestration of C Cavern Pressure Response  CO 2 is always in a supercritical state  Salt exhibits slow creep closure  Slow closure gradually pressurizes CO 2  Long-term pressure response is only weakly sensitive to filling pressure  In ~4000 years, p c ~ 94% of  v  Final density approaches 0.92 g/cm 3

Geological Sequestration of C Subsidence at the Surface? Z ~ 1200 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 5  Z 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 Response  For the following case:  Single 100 m Ø cavern, V i ~ 500,000 m 3  Filled to 14 MPa (pressure of a brine column to the surface)  Cavern sealed in perpetuity  Volume change in cavern ~ 78,000 m 3  2.5 mm displacement in first 150 yrs  2.5 mm thereafter (as t   )

Geological Sequestration of C Sequestration Security Issues

Geological Sequestration of C Leakage Mechanisms low permeability high permeability brines,  = 1.2 salt fresh water,  = 1.0 fracture  p advection wellbore wellbore leakage permeable interbeds

Geological Sequestration of C Security? Depth in Metres 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 Formation Ernestina Lake Fmn Lotsberg Salt Basal Red Beds Igneous, metamorphic rocks Ductile shales (k v ~ 0) Flat-lying strata No faults, folds Massive salts (k v = k h ~ 0)

Geological Sequestration of C Regional 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 m  Water-filled porous strata  CO 2 can go into solution if it escapes

Geological Sequestration of C Secure Cavern Design Overlying salt beds Non-shrinking, ductile cement Special squeezed cement seals Salt-occluded porosity in bounding strata m overlying salt barrier m high “spherical” cavern Thick lateral salt beds m lower salt barrier Salt-occluded porosity in Red Beds

Geological Sequestration of C Cavern-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 CONCLUSIONS  The Lotsberg Salt is an exceptionally favorable deposit for CO 2 storage  The regional geology also is favorable  Two caverns (~10 6 m 3 ) could take Al- berta point CO 2 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…  Generally available competitive H 2 fuel cell cars at least 20 years away  Biosolids injection will be a huge industry in years  Separation, deep injection of gaseous, supercritical CO 2 may happen…(?)  Nuclear energy is poised for a major comeback (no CO 2 !)  Taxes are going to go up