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

Geological Sequestration of C C Sequestration  As CO 2  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 CO 2 used to access resources, is a byproduct of an valuable process, …  Sequestration is a +ve but secondary factor

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 -… …

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

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

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

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

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 70%  Miscible CO 2 can take R F up to 70-90%

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 place 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…

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?

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

Geological Sequestration of C Pure CO 2 Behavior  Gaseous state  Low density, low viscosity, under low p, T  Liquid state  High density, low μ, high p, low T <35ºC  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

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 Depth below ground - m T - ºC T SC Typical range of T with depth

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 Depth below ground - m T - ºC T SC p SC liquid gas liquid SC-CO 2

Geological Sequestration of C Gaseous CO 2 Use in Recovery

Geological Sequestration of C Technologies for CO 2 use  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)  In shallow reservoirs, CO 2 as an inert gas to aid gravity drainage  Miscible CO 2 flooding (Weyburn, SK…)

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

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

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

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

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

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…

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: S o, S w, S g  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 CO 2 Distribution

Geological Sequestration of C Dissolved CO 2 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 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!

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…

Geological Sequestration of C Pure CO 2 Phase Behavior

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