1. Geological Sequestration of C Carbon Sequestration in Sedimentary Basins Module II: Physical Processes in C Sequestration… Maurice Dusseault Department of Earth Sciences University of Waterloo

2. Geological Sequestration of C C Sequestration  As CO 2  An enhanced oil or gas recovery agent  Displacing formation water in deep aquifers  Dissolved in the aqueous phase  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

3. Geological Sequestration of C Is Separation Best?  Costly process…  Membranes (not quite there yet)  Forced adsorption (amine solutions, etc.)  High reactivity calcium oxide  Cryogenic (low T methods)  These would all double the cost of power in current configurations  Modification of combustion process?  New sequestration method?

4. Geological Sequestration of C Coal power with CO 2 separation 1982 Lubbock, Texas. The plant was based on an oil price of 30$/barrel and was discontinued when the oil prices was sinking in the late 1980’s. Only the (now mothballed) MEA separation plant is shown. The power plant itself is still running and is located to the right of the picture

5. Geological Sequestration of C CO 2 -capture Pilot Plant at Kaarstoe – Norway: Capture from exhaust gas by use of membrane/amine technology

6. Geological Sequestration of C Carbon Sequestration Options  Store CO 2 as SC fluid in depleted reservoirs, suitable traps  Dissolve CO 2 into deep fluid reservoirs  Use CO 2 in Enhanced Recovery to displace oil or gas from strata  Deep slurry injection of biosolids, coal, or any other solid organic waste  Place CO 2 in a dissolved salt cavern (the NaCl brine is industrial feedstock)

7. Geological Sequestration of C CO 2 Behavior…  Extremely complex (p, T, chemistry…)  Oil swelling with CO 2 adsorption  Interfacial tension issues (changes as a function of p, T, oil chemistry…)  Diffusion rates into H 2 O, oil…  Phase relationships in mixtures of gases, liquids (e.g SC-CO 2 + oil + H 2 O), …  Changes in rock wettability…  Formation of hydrate phases…

8. 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 CO 2 used to access resources, is a byproduct of an valuable process, …  Sequestration is a +ve but secondary factor

9. Geological Sequestration of C HC Enhanced Recovery with CO 2  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  CO 2 can improve the recovery factor  CO 2 largely left behind – i.e.: sequestered

10. Geological Sequestration of C CCS – CO 2 Capture & Seques.  CO 2 is captured from some source  Or, flue gas is used, (partly enriched?)  It is injected into the ground, into suitable porous and permeable media  The CO 2 stays there indefinitely Typical Issues: -Capacity and rate -Value-added process? -Economics -Long-term fate -… …

11. Geological Sequestration of C Alberta Research Council CO 2 capture +C-rich coal waste injection

12. Geological Sequestration of C CO 2 Behavior We must understand the behavior of CO 2 and the site conditions!

13. Geological Sequestration of C Pure CO 2 Behavior  Gaseous state storage…  Low density, low viscosity, under low p, T  Liquid state storage…  High density, low μ, high p, low T <35ºC  Not compatible with real reservoirs  Supercritical state, > 35ºC, > 7.2 MPa  (> 95ºF, > 1035 psi, approximately)  High ρ, low μ,  Fully miscible with water and oil  Hydrate formation – low T, high p, +H 2 O

14. Geological Sequestration of C Depth and CO 2 State - I…  T increases w. depth ~20-25ºC/km  In most areas, T > 35ºC below ~800 m  In cold conditions, pure CO 2 will be in a a liquid state  In the presence of water and high p, a CO 2 -H 2 O clathrate (hydrate) forms 0 1000 2000 204060 0 Depth below ground - m T - ºC T SC ~35°C Typical range of T with depth 7.2 MPa Practical conditions for CO 2 placement

15. Geological Sequestration of C Depth and CO 2 State - II…  Most reservoirs to Z = 3 km: hydrostatic pressures ~10 kPa/m  Pure CO 2 is SC below ~750 m, if T > 35ºC  In general, CO 2 is a supercritical fluid at Z > 800 m (~2620’)  Otherwise, it is a gas or a liquid, depending on p & T 0 1000 2000 204060 0 Depth below ground - m T - ºC T SC p SC liquid gas liquid SC-CO 2

16. Geological Sequestration of C Technologies for CO 2 use  In shallow reservoirs, CO 2 as an inert gas to aid gravity drainage  Displace CH 4 from coal seams  Deeper seams could be depressurized so p inj < p SC for CO 2  CO 2 could be used to “chase” gas from low permeability reservoirs (solubility in water may help considerably)  Miscible CO 2 flooding (Weyburn, SK…)

17. Geological Sequestration of C Inert Gas Injection (Δρ process) dmdm oil gas water pp Generally, it is a top down displacement process, gravitationally assisted and density stabilized Note: in a water-wet reservoir, a continuous 3-D oil film exists, providing that   wg >  og +  wo Gas is injected high in the reservoir to move the oil interface downward Recovery % can be high

18. Geological Sequestration of C IGI, With Reservoir Structure oil bank, two-phase zone water-wet sand horizontal wells parallel to structure inert gas injection keep  p to a minimum gas rates are controlled to avoid gas (or water) coning three-phase zone if coning develops, drop pressures! best to monitor the process; mainly gas water, one phase  pp

19. Geological Sequestration of C Is Inert Gas Injection Useful?  For IGI, a gas phase is needed for gravitational segregation and drainage  So, CO 2 must remain in a gaseous phase  Density is less than 0.05  Hence, the mass of CO 2 that can be sequestered is trivial  CO 2 use in gravity drainage methods is of no value to sequestration needs  Supercritical CO 2 is needed

20. Geological Sequestration of C Miscibility of Oil and CO 2 68 bar – 1000 psi Immiscible CO2 102 bar – 1500 psi Miscibility begins to develope 170 bar – 2500 psi CO2 has developed miscibility Higher hydrocarbons (dark spots) begins to condense Final stage: Higher HC forms continuous phase- CO2 immiscible

21. Geological Sequestration of C Miscible Conditions

22. Geological Sequestration of C CO 2, then a Water Slug, etc.

23. Geological Sequestration of C Cyclic CO 2 (also in THEOR)

24. Geological Sequestration of C N 2 ? Only at very great depth…

25. Geological Sequestration of C CO 2 - EOR CO 2 Injection CO 2 OIL Recycled CO 2 Production Well Reservoir Cap-rock or seal Other permeable and non-permeable strata ΔpΔp

26. Geological Sequestration of C Oil Production Phases… Time Oil Rate Phase I: Primary Depletion – Δp Phase II: Water Flood, Δp-maintenance Phase III: CO 2 miscible injection I II III

27. Geological Sequestration of C Why Different Phases?  History – CO 2 -EOR relatively new (1972)  Economics  Primary energy is the cheapest method  Waterflood, often re-injection of produced H 2 O, is not as cheap, but still not costly  CO 2 is relatively expensive, in comparison  Recovery Factors - R F  Primary R F from 20-40% (average ~  )  Waterflood takes R F up to 30 to ~55%  Miscible CO 2 can take R F up to 80-85%

28. Geological Sequestration of C Potential for CO 2 in EOR  World-wide, perhaps 100 × 10 9 m 3 oil could be recovered with CO 2 -EOR in a supercritical or liquid state  To recover 1 m 3 of oil, likely we will have to inject from 0.5 to 2 m 3 of SC-CO 2, ρ ~ 0.80, into the reservoir permanently  Mass sequestered =  100 × 10 9 m 3 · 0.80 t/m 3 · 0.5 = 40 Gt  Other assumptions, other figures…

29. Geological Sequestration of C Miscibility of Oil and CO 2 68 bar – 1000 psi Immiscible CO2 102 bar – 1500 psi Miscibility begins to develope 170 bar – 2500 psi CO2 has developed miscibility Higher hydrocarbons (dark spots) begins to condense Final stage: Higher HC forms continuous phase- CO2 immiscible

30. Geological Sequestration of C Exploring Some Possibilities…  Oil reservoirs suitable for CO 2 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 CO 2 behave?  Technical options for oil recovery?  Does CO 2 injection fit in with these?

31. Geological Sequestration of C HC Enhanced Recovery with CO 2  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  CO 2 can improve the recovery factor  CO 2 largely left behind – i.e.: sequestered

32. Geological Sequestration of C Physical Properties…  Porosity - φ - controls storage volume available:  φ = fractional void space of the rock V of solid mineral Void space (fluids) φ 1 - φ

33. Geological Sequestration of C Physical Properties…  Permeability is the ability to transmit fluid (gas or liquid or SC-fluid) ΔpΔp L A L = 40 – 100 mm In the field, “L” = 100 – 2000 m

34. Geological Sequestration of C Fluids - Oil, H 2 O, Gas, CO 2 …  Viscosity = ƒ(T…), Salinity (of H 2 O)  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 CO 2  Surface tensions  Asphaltene%, Other oil characteristics  And so on…

35. Geological Sequestration of C CO 2 Solubility in Water This is at 1.0 atmosphere pressure. Increasing T means lower solubility

36. Geological Sequestration of C T Effects on CO 2 Solubility  CO 2 solubility decreases with T until about 100ºC  At higher T, solubility starts to increase with T

37. Geological Sequestration of C N 2 Solubility in Water N 2 is less than 1/10 th the solubility of CO 2 at atmospheric pressure

38. Geological Sequestration of C Gas Solubility in Water  In water, N 2 and CH 4 are about 1/10 th the solubility of CO 2  (Oxygen is slightly more soluble than CH 4 but we don’t worry about it)  Hence, water will absorb and hold a lot more CO 2, stripping it from flue gas  We have also to look at the issue of pressure (≈ depth  10 kPa/m)

39. Geological Sequestration of C p-T Solubility of CO 2 in H 2 O http://www.kgs.ku.edu/PRS/publication/2003/ofr2003-33/P 1-05.html Above 1050 psi, CO 2 approaches supercriticality

40. Geological Sequestration of C CO 2 … Higher p: Larger amount of CO 2 in solution h = 298.15 mol/ kg * bar

41. Geological Sequestration of C Pressure Solubility, CO 2 in H 2 O  As p goes up, more gas in solution  Henry’s Law for ideal gases: V(gas) STP in solution = h  p  V(water)  Henry’s constant h ~ 0.832 m 3 /m 3 /atm, but only for dilute solutions well below p c - the critical pressure  Once p c is approached, the system departs from linearity, and then CO 2 becomes fully miscible with H 2 O

42. Geological Sequestration of C Effects of p on CO 2 Solubility  At constant T and constant salinity, the solubility of CO 2 increases directly with pressure  However, this pressure solubility effect decreases with increasing p  So, at lower pressures the solubility increases more rapidly than at higher pressures

43. Geological Sequestration of C CO 2 Solubility in Brine Sea water The effect of dissolved NaCl

44. Geological Sequestration of C Salinity & CO 2 Solubility in H 2 O  Addition of any salt (usually NaCl of course), leads to a decrease in the solubility of CO 2 in water  There are effects of the nature of the salt (NaCl is worst than divalent soalts such as CaCl 2 )  So, saturated brine is not as good as fresh water!  In presence of reactive minerals……?

45. Geological Sequestration of C …and, the Effect of pH! Natural waters

46. Geological Sequestration of C Reservoir Conditions  Pressure (in the fluids)  Temperature  Stress (solid rock matrix)  pH  Current bubble point pressure of liquids  Gas-to-oil ratio in situ  Saturations: S o, S w, S g  Production history, well test data…

47. Geological Sequestration of C What Will Governments Require?  New Class VI wells (US-EPA), will need…  Geomechanical analysis of injection ops.  Analyze & report induced seismicity potential as the result of injection ops.  Integrated modeling & monitoring prog.  Compositional modeling recommended…  Monitoring methods to be negotiated…  p measurements in overlying formation  CO 2 plume geophysical monitoring

48. 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 and properties  Contaminating gases and phase behavior…  Calibration, if possible, then predictions  Prediction confirmation by monitoring…

49. Geological Sequestration of C Gaseous CO 2 Distribution

50. Geological Sequestration of C Dissolved CO 2 Distribution

51. 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

52. Geological Sequestration of C Interfacial Tensions  In the immiscible state, the CO 2 that remains undissolved has a surface tension with water ƒ(p, T, salinity…)  With SC-CO 2, 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!

53. Geological Sequestration of C CO 2 Behavior…  Extremely complex…  Oil swelling with CO 2 adsorption  Interfacial tension issues (changes as a function of p, T, oil chemistry…)  Diffusion rates into H 2 O, oil…  Phase relationships in mixtures of gases, liquids (e.g SC-CO 2 + oil + H 2 O), …  Changes in rock wettability…  Formation of hydrate phases…

54. Geological Sequestration of C Pure CO 2 Phase Behavior

55. Geological Sequestration of C p-T-ρ EOS Weyburn conditions – ~15 MPa, ~45ºC

56. Geological Sequestration of C Gas Migration, Segregation Shale caprock Sandstone Base rock Biosolids Gas cap Gas bubbles Injection well, later converted to a gas production well

57. Geological Sequestration of C Chromatographic Gas Cleaning…  CH 4 (75%), CO 2 (25%), a bit of H 2 S, NO x  These gases start to bubble upward  But, the aqueous phase absorbs gas until it is saturated with each specie  CH 4 is very insoluble (< 0.01 v/v/atm)  CO 2 & H 2 S are highly soluble  As gases migrate upward, these are stripped by dissolution, but not CH 4  Slow moving H 2 O carries CO 2, H 2 S away

58. Geological Sequestration of C Flat-Lying Aquifer Strata N 2 withdrawal Nitrogen 2-phase gas- water region horizontal wells vertical wells  p ~ 0 N 2 withdrawal The system must be operated at ~gravity drainage conditions to avoid water coning to the withdrawal wells

59. Geological Sequestration of C

60. Chromatographic N 2 Stripping  Flue gas is N 2 (87%), CO 2 (13%), a bit of H 2 S, NO x  These gases bubble upward  N 2 far less soluble, H 2 O becomes CO 2 saturated, N 2 goes to top of reservoir  Forced gravity convection renews H 2 O  Slow moving H 2 O carries CO 2, H 2 S away dissolved in the aqueous phase  N 2 released to atmosphere…

61. Geological Sequestration of C Reefs and CO 2 horizontal well trajectory below the well are only lower permeability reef strata, k too low for economical injection gas injection uniform along well path low  p maintained previous injection/ production wells converted to gas withdrawal wells horizontal well placement based on permeability nitrogen vertical wells N 2 withdrawal

62. Geological Sequestration of C N 2 production well Configurations with different combinations of vertical and horizontal wells may be envisioned N 2 production well Staggered Well Injection Injection well The bubbling gas generates forced H 2 O convection, bringing fresh water with less CO 2 to the horizontal well region

63. Geological Sequestration of C 63 Complex Well Arrays In principle, if gas can be uniformly injected, it is best to have as much length as the compressors can handle. Should we cool the gas before injection into the reservoir? High T reduces CO 2 solubility… Careful analysis is always needed…

64. Geological Sequestration of C IGI, With Reservoir Structure horizontal well parallel to structure N 2 withdrawal keep  p to a minimum rates are controlled to avoid gas (or water) coning mainly gas Gas segregation is an issue… Water and gas

65. Geological Sequestration of C CO 2, with Reservoir Structure horizontal well at 90° to strike N 2 withdrawal keep  p to a minimum Rates are controlled to avoid gas (or water) coning. mainly gas Gas segregation is an issue… water and gas The presence of shale layers can help mixing in this case.

66. Geological Sequestration of C How Much CO 2 in H 2 O?  Depends on p in the aquifer (partial pressure of CO 2 )  Depends on the T of the reservoir  Depends on the pH of the water  Depends whether it is carbonate or not  Depends on the salinity of the H 2 O  Depends on other solutes  So, to calculate the capacity…

67. Geological Sequestration of C More Coupling…  CO 2, H 2 S gases dissolve in the water  Gravity segregation occurs, displacing water from the system; gravity drainage flow model + forced convection  Liquid flux carries dissolved gases away  The cleaned N 2 gas produced through upper well (p-V-T effects in reservoir)  The CO 2 dissolved in water is sequestered…