Carbon Dioxide Properties and the Role of Impurities in the Subsurface

J P Martin Trusler

Department of Chemical Engineering &

Qatar Carbonates and Carbon Storage Research Centre Imperial College London, U.K.

UKCCS Research Centre, Biannual Meeting, Cardiff, 10 September 2014

CCS, CO2 Properties, Mixtures and Impurities

• Fluid properties are fundamental to all aspects of CCS • But it’s not just CO2 – many complex mixtures involved:

– Fuels and combustion gases from which CO2 is captured – Mixtures formed with inevitable impurities – Mixtures formed with brine and/or hydrocarbons when the injected

into a geological storage sink

• Hence there are huge variety of complex mixtures involved • Also a very wide range of conditions in CCS from low

pressures to 100 MPa, cryogenic temperatures to 1000°C • And a need to understand physical and chemical properties

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CCS Landscape, Properties, Mixtures and Impurities

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0.1

1

10

100

200 250 300 350 400

p/M

Pa

T/K

Gas

Liquid

Solid Super-Critical Fluid

Pipeline Storage

Capture & Compression

Mixtures and Impurities • Diluents:

• N2 • O2 • H2

• Acid Gases: • H2S • SO2

• Aqueous species: • H2O • Salts

• Hydrocarbons: • Gas • Condensates • Oils

• Others: • NOx • Trace elements

• Phase behaviour • Density • Viscosity • Diffusion coefficients

• Interfacial tension • Contact angle • pH • Reactivity w/ minerals

Properties

Storage

• Focus on deep saline aquifers and depleted oil fields • Need to consider the mixtures formed when CO2 contacts

the reservoir fluid: brines and hydrocarbons • … and allow for impurities present in the CO2 stream • Would like to predict:

– rate of dissolution of CO2 and impurities – buoyancy and convective flow of the resulting solutions – reactivity towards reservoir minerals

• Controlling physical/chemical properties: – solubility, diffusion coefficients – density, viscosity – pH, rate constants

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Role of Impurities in the Subsurface

• Diluents – much less soluble in brine than CO2

– raise interfacial tension against brine – may build up in mixing/dissolution zones

• Other acid gases – more soluble than CO2

– lower interfacial tension against brine – reactive towards carbonate minerals

• Hydrocarbons – very low solubility in brine – unknown influence on CO2 storage in saline aquifers

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QCCSRC Research Programme

• Wide ranging programme aimed at understanding CO2 storage in carbonate reservoirs – Geology, geochemistry, geophysics – Multiphase reactive flow in porous media – Thermophysical properties – Reservoir modelling

• Thermophysical properties work packages – Phase I: CO2/brines/hydrocarbon systems - Completed – Phase II: Effects of impurities in the CO2 stream - Active – Both involving experimental measurements and modelling

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QCCSRC Thermophysics Workflow

7

Water

CO2

Impurities

Hydrocarbons

Minerals

pVT:Analytical VLESynthetic VLE

Density

Mol

ecul

ar M

odel

ling

Interfacial Properties:

IFTContact angle

Chemical Properties:

KineticspH

Salts

Oil - CO2Systems

Brine - CO2Systems

Brine - CO2 -MineralSystems

Components Mixtures Properties Outputs

Data

Needs

Data

Needs

Data

Needs

Experiment design

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Interfacial Tension of CO2 + Brines at Reservoir Conditions

Significance: Interfacial tension γ and contact angle θc determine the capillary entry pressure pc for a pore of radius r, and thus the over pressure needed to displace brine by CO2 during an injection process Young-Laplace equation: pc = (2γ/r) cosθc

Pendant-Drop Apparatus for Interfacial Tension

9

P

DE DE

R0 θ

x θ

y

DS

O

Hastelloy and titanium cells rated for p = 50 MPa at T = 473 K.

Vent

P4

P2

P3

P1

Magnetic Stirrer Bar

V2

V1

N2

N1

Vent

V3

V4

V5

V6

Inlet 1

Inlet 2

Inlet 3

Inlet 4

C1

T

P

V7

βρΔgRγ /20=

IFT of (0.864 NaCl + 0.136 KCl) (aq) at m = 3 mol·kg-1

10

25

35

45

55

65

75

0 10 20 30 40 50

γ/(m

N/m

)

p/MPa

323.15 K

423.15 K

T = 298.15 K

25

35

45

55

65

75

0 10 20 30 40 50

γ/(m

N/m

)

p/MPa

Liquid-Liquid

Gas-Liquid

Pure water Pure brine

T > Tc

Li et al. J. Chem. Eng. Data. DOI: 10.1021/je201062r (2012).

IFT for the (CO2 + N2 + H2O) System

11

15

25

35

45

55

65

75

0 10 20 30 40

Υ/m

N∙m

-1

p/MPa

15

25

35

45

55

65

75

0 10 20 30 40Υ

/mN

∙m-1

p/MPa

15

25

35

45

55

65

75

0 10 20 30 40

Υ/m

N∙m

-1

p/MPa

15

25

35

45

55

65

75

0 10 20 30 40

Υ/m

N∙m

-1

p/MPa

298 K 323 K

373 K 448 K

N2 + H2O correlation

CO2 + H2O correlation

(0.5CO2 + 0.5N2) + H2O data

Mole-fraction-weighted average

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Phase Behaviour of CO2 with Brines at Reservoir Conditions

Measurements with: • Static-Analytic Apparatus for Coexisting Water- and CO2-Rich Phases • Static-Synthetic Apparatus for CO2 Solubility in Brines

Static-Analytic Apparatus (298 to 450) K @ p ≤ 50 MPa

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`

30.000 C

Temperature Readout

Gas Chromatography

1320

Pressure Transducer

Brine

Hydrocarbon

CO2 Magnetic Pump

Equilibrium Cell

Thermometer Probe

Rolsi Valve

Filter

Vindum Valve

Cross

Reducer

Tee

Vaccum Pump

Drain

Safety Head

Needle Valve

Check Valve

Tube Heater

Results for CO2 + NaCl(aq)

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T = 323.15 K • Measurements from 298 K to 443 K with pressures to 18 MPa

• Modelling with asymmetric approach:

• eNRTL for the aqueous phase

• Peng-Robinson EoS for the gas phase

• Good account of CO2 solubility in the liquid phase

• Imperfect description of the gas phase

Hou et al. J. Chem. Eng. Data. DOI: 10.1016/j.supflu.2013.03.022 (2013).

T = 423.15 K

Static-Synthetic Apparatus (298 to 473) K @ p ≤ 50 MPa

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Vacuum

P

SP

C1

V2 V1

T

V3 Drain

V4

PG

• Little CO2 solubility data have been reported for complex brines under reservoir conditions

• Interest in mixed brines, including bivalent cations such as Ca2+, Mg2+

• pH is also of special interest

Solubility of CO2 in MgCl2(aq)

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, T = 309 K; , T = 345 K; , T = 375 K; , T = 424 K

• Experimental measurements from 309 K to 424 K with pressures up to 35 MPa • CaCl2(aq) also studied • Modelling with Krichevsky-Kasarnovski model:

RTppVHxf /)(ln)/ln( ref11211 −+= ∞

m = 1 mol/kg m = 3 mol/kg m = 5 mol/kg

Tong et al. J. Chem. Eng. Data. DOI: 10.1021/je400396s (2013).

Other QCCSRC Thermophysics Research

Completed: • Viscosity of CO2-saturated water/brine • Diffusion coefficients of CO2 and N2 in water/brine • Kinetics of carbonate dissolution in CO2-saturated water • pH of CO2 saturated water/brine • Phase behaviour studies of CO2-hydrocarbon mixtures In progress: • Coexisting phase densities of CO2 + water • Solubility of H2S and SO2 in water and brine at HTHP • More phase behaviour studies of CO2-hydrocarbon mixtures • Effect of impurities on CO2-water IFT • Solubility of light hydrocarbons in water/brine

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Research Team: • John Crawshaw • Shuxin Hou • Saif Al Ghafri • Yolanda Sanchez • Mihaela Stevar • David Vega • Chidi Efika • Shane Cadogan • Xuesong Li • Cheng Peng

• Mark McBride-Wright

• Benaiah Anabaraonye

• Claudio Calabrese

• Florence Chow • Rayane Hoballah • Ruien Hu

Acknowledgements

Co-Investigators • Geoff Maitland • Edo Boek Collaborators • Amparo Galindo • George Jackson • Andrew Haslam • Velisa Vesovic

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We gratefully acknowledge funding from QCCSRC, provided jointly by Qatar Petroleum, Shell, and Qatar Science & Technology Park