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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
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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 option much
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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?
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Geological Sequestration of C CO 2 Purity, Various Sources Ammonia 100% Hydrogen 10-100% Ethylene oxide 100% Gas processing 100% Cement 15-30% (CaCO 3 …) Iron and steel 15% Ethylene10-15% Refineries 3-13% Power 3-15% (13/87 flue gas)
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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
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Geological Sequestration of C CO 2 -capture Pilot Plant at Kaarstoe – Norway: Capture from exhaust gas by use of membrane/amine technology
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Geological Sequestration of C Separation Options… Absorption: fluid dissolves or permeates into a liquid or solid. Adsorption: attachment of fluid to a surface (solid or liquid). Cryogenic (low-temperature distillation): separation based on the difference in boiling points of N 2, CO 2 … Membranes: separation based on different physical & chemical interactions with membrane (molecular weight, molecular diameter, solubility…)
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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) Mineral reaction with peridotite…
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Geological Sequestration of C Example, Cryogenic Separation Distillation at low T… Applied to separate CO 2 from natural gas, O 2 from N 2 and Ar in air, or CO 2 from flue gas. substanceBoiling point (°C@p 0 ) Triple point (°C, bar) CO 2 NA (sublimation)-57, 5.18 CH 4 -162-183, 0.12 O2O2 -183-219, 0.0015 N2N2 -196-210, 0.125 Ar-186-199, 0.69
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Geological Sequestration of C Example, Membrane Use feed is “X-rich” retentate site, higher pressure output is “X poor” sweep gas (coaxial-flow or countercurrent flow) membrane “X” is a gas specie that passes more easily through the membrane XX rich in permeating specie
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Geological Sequestration of C Graded Porosity Membrane… made of the same material.
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Geological Sequestration of C Separation of CO 2 from CH 4 …
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Geological Sequestration of C Peridotite Absorbs CO 2 … Copyright 2008 by Andrew Alden, geology.about.com, reproduced under educational fair use Peridotite from California
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Geological Sequestration of C Peridotite-Rich Ophiolites… OMAN Semail Ophiolites
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Geological Sequestration of C CO 2 Adsorption… Minerals change to carbonates Drill holes 4-8 km deep, inject hot water saturated with CO 2 at high pressures Reaction is exothermic - T -accelerates No risk of “escape”… OMAN
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Geological Sequestration of C Is it Realistic? Likely, far less than sequestering CO 2 in reservoirs… More costly Limited areas in the world with large peridotite volumes (none in Canada) Nevertheless… research continues, as it must…
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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…
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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
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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 Biosolids injection (CH 4 generated…)
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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 -… …
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Geological Sequestration of C Alberta Research Council CO 2 capture +C-rich coal waste injection
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Geological Sequestration of C CO 2 Behavior We must understand the behavior of CO 2 and the site conditions!
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Geological Sequestration of C CO 2 Behavior…
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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
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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
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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
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Geological Sequestration of C Depth and Density of CO 2 … (kg/m 3 )
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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…)
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Geological Sequestration of C Inert Gas Injection (Δρ process) dmdm oil CO 2 water pp 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
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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 pp
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Geological Sequestration of C CO 2, then a Water Slug, etc.
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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
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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
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Geological Sequestration of C Miscibility… Natural gas or N 2 and CO 2 mixtures are fully miscible; they form a single fluid phase CO 2 (liquid or supercritical) and water are immiscible (but CO 2 can dissolve readily in water!) CO 2 and oil are miscible or immiscible depending on oil composition and thermodynamic conditions (p, T) CO 2 and Coal: very complex; surface adsorption also plays a role
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Geological Sequestration of C Miscible Conditions
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Geological Sequestration of C Viscosity of SC-CO 2 Viscosity of water (H 2 O) @ STP is 1.0 MPa s
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Geological Sequestration of C Is SC-CO 2 Viscosity Important? The rate we can inject into a porous permeable reservoir depends on it… Low viscosity = much easier to do However! Low viscosity leads to the problem of viscous fingering… The low viscosity phase does not dis- place the high viscosity phase uniformly Similar to trying to waterflood heavy (viscous) oil…
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Geological Sequestration of C Viscous Fingering… Oil – viscosity is 35 MPa s Water is displac- ing the oil, viscosity ~ 1 MPa s Unstable fingering develops Of course, these two phases are immiscible
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Geological Sequestration of C Cyclic CO 2 (also in THEOR)
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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
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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
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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%
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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…
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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
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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?
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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
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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
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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
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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…
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Geological Sequestration of C CO 2 Solubility in Water This is at 1.0 atmosphere pressure. Increasing T means lower solubility
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Geological Sequestration of C CO 2 Dissolution in H 2 O
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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
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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
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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)
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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
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Geological Sequestration of C CO 2 … Higher p: Larger amount of CO 2 in solution h = 298.15 mol/ kg * bar
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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
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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
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Geological Sequestration of C CO 2 Solubility in Brine Sea water The effect of dissolved NaCl
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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 worse than divalent salts such as CaCl 2 ) So, saturated brine is not as good as fresh water for CO 2 dissolution! In presence of reactive minerals……?
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Geological Sequestration of C …and, the Effect of pH! Natural waters
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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…
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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
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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…
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Geological Sequestration of C CO 2 Distribution with Time
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Geological Sequestration of C Dissolved CO 2 Distribution
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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 Degradation of capillary barriers to SC-CO 2 Other concerns?
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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!
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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…
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Geological Sequestration of C Pure CO 2 Phase Behavior
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Geological Sequestration of C p-T-ρ EOS Weyburn conditions – ~15 MPa, ~45ºC
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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
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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
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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
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Geological Sequestration of C
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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…
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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
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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
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Geological Sequestration of C 79 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…
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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
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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.
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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…
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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…
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