CO2 Sequestration Potential of Charqueadas Coal Field in Brazilq

Vyacheslav RomanovNational Energy Technology Laboratory

Pittsburgh, October 23-24, 2012

The technical effort was performed in support of the National Energy Technology Laboratory’s on-going research in carbon Sequestration, partly under the RES contract DE-FE000-4000.

The project was sponsored by the U.S. DOE within framework of Carbon Sequestration research program

Teamand MOU with Pontificia Universidade Catolica Do Rio Grande Do Sul (PUCRS).

NETL (federal)Vyacheslav N. RomanovR b t P W i kiRobert P. Warzinski

NETL-URSDustin CrandallIgor V. HaljasmaaJames J. Fazio

NETL University of Pittsburgh (RUA)NETL-University of Pittsburgh (RUA)Tae-Bong Hur

PUCRS (Brazil)Cristian S. Santarosa

PETROBRAS-CEPAC (Brazil)Roberto Heemann

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Roberto HeemannJ. Marcello M. Ketzer

Background

The core samples used in the study were obtained as part of a joint initiative between PETROBRAS and CEPAC in 2010, to evaluate h i l f i l d i d COthe potential for unconventional gas production and CO2 storagein the Charqueadas coal seams.

The pilot site was chosen in Porto Batista, Charqueadas coal field, b t 60 k t f P t Alabout 60 km west of Porto Alegre.

There are six coal seams in this area, named SB, MB, I1F, I1Fa, I2B, I3F (from top to bottom), but only three of them, MB, I1F, and I2B

id d t t f CBM d ti d CO i j tiwere considered as targets for CBM production and CO2 injectionowing mainly to their thickness and rank.

The overall goal of this work is complementary to the joint initiative of PETROBRAS d CEPACPETROBRAS and CEPAC.

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Project Objectives

• Although coal is not the primary source of energy in Brazil there is growing interest to evaluate the potential of coal from the south of the country for various activities.

• The I2B coal seam in the Charqueadas coal field has been evaluated as a target for enhanced coal bed methane production and CO2 sequestration.

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Scope of WorkThe samples were low rank coals (highThe samples were low rank coals (high volatile bituminous and sub-bituminous) obtained from the I2B seam as Ø3” cores (left).

Such properties as sorption capacity, internal structure of the samples, porosity and permeability were of primary interest in this p y p ycharacterization study.

Some samples were sub-cored to Ø1.5” (below); the others were crushed to pass a(below); the others were crushed to pass a 100-mesh screen for powder sorption isotherm tests.

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Sample Characterization

Sample

Canister

Depth

(m)

Moisture

(%)

Volatile

matter (%)

Ash content

(%)

Fixed

carbon (%)

C-13 339.0 4.06 18.98 49.67 27.46

C-14 339.5 4.40 18.59 58.08 19.11

C-25 346.3 4.64 22.73 46.66 26.19

C-28 347.6 4.27 18.90 51.82 25.19

C-29 348.2 4.73 23.46 43.32 28.70

Micro CT image of a sub sample of C 14Proximate analysis was carried out according to Micro-CT image of a sub sample of C-14Even though this C-14 sample was observed to be ‘uniform’ in the medical CT scans, this higher resolution scan reveals that there is a large amount of

y gBrazilian standards (ABNT DBR) corresponding to the ASTM certified methods (D3172 - 07a and D7582 -10e1).

reveals that there is a large amount of variability in the core. The micro-fractures most likely provide pathways for CO2 to enter the coal matrix, while the shale increases the overall

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resilience of the core to external stressing.

Porosity and Permeability Measurements

(A)TEMCO helium porosimeter, HP-401

(B) AutoLab-1500 (NER, Inc.) with installed core holder (zoom-in)

Medical CT Scanner

Universal Systems HD350-E 4th generation;140 kV and 400 mA, resolution 0.25 mm X 1 mm.Sub-cores of coal were exposed to CO2 over three week periods within TEMCO

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three week periods within TEMCO composite core holder 401 and a Buna-N sleeve

Composite core-holder (CT)

Sub-cores of coal were exposed to CO2 over three week periods within the TEMCO it h ld 401 (C L b I t t T l OK) A lTEMCO composite core holder 401 (Core Lab Instruments, Tulsa, OK). A coal sample was placed within a Buna-N sleeve and enclosed within the composite core holder. After centering the core holder in the medical CT scanner gantry chucks, high pressure ISCO model 260D pumps were used to apply axial and radial confining pressures to the coal core.

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g p

Mechanical Properties

Dilation

Densityy

ρ = A × CTNHigh + B × CTNLow + C

Young’s modulus

(assumed ν = 0.3)

Dual-energy scanning enables accurate estimates of density from CT scanning by obtaining CT number (CTN) above and below the threshold of Compton scatteringobtaining CT number (CTN) above and below the threshold of Compton scattering.

High-energy scans were performed at 140 keV and low-energy scans were performed at 80 keV. Aluminum, graphite and fused quartz were scanned throughout the experiments to determine A, B and C, and to ensure that the CTN did not vary throughout the testing.

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RESULTS (mechanical properties)C-13 (D = 38 mm, L = 47.4 mm) had 1.6 % porosity and about 140 nD permeability

C-25 (D = 37.87 mm, L = 60.55 mm) had 4.3 (initial) to 3.4 (final) % porosity and about 340-730 nD permeability

C-29 had permeability below detection limit

0 450.50

Pa

C-25 core sample (CT):E does not reach a stable value, even with a confining pressure of 11.1 MPa. This0.30

0.350.400.45

ulus

, GP

pressure of 11.1 MPa. This suggests that micro-cracks will be open within the in-situ coal.

0.150.200.250.30

g's

Mod

u

Increasing P

0.000.050.10

0 5 10 15

Youn

g Increasing PDecreasing P

10

0 5 10 15

Confining Pressure, MPa

CT scanning prior to CO21 8 (C)

1.5

1.6

1.7

1.8

y, g/

cc

C-14C-25

(C)(D)

1.2

1.3

1.4

Den

sity

1.10 10 20 30 40 50 60

Length along core, mm

(C)( )

False color montages from medical CT scanner. Higher density material is shown as bright yellows while dark

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purple and orange are lower density. Each slice is 2 mm thick and has a pixel resolution of 0.25 mm by 0.25 mm.

1 8

CT scanning prior to CO2

1.5

1.6

1.7

1.8

y, g/

cc

C-14C-25(C-14)

1.2

1.3

1.4

Den

sity

1.10 10 20 30 40 50 60

Length along core, mm

C-14 was used as a representative sample from the(C-25)

C-14 was used as a representative sample from the upper section of I2B and C-25 as a representative sample from the lower section of I2B.

Brighter regions correspond to high-density zones and darker regions indicate lower-density areas.

Upper seam is shown to be fairly uniform in material structure, while numerous mineralized

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material structure, while numerous mineralized fractures are apparent in lower seam.

RESULTS (sorption in cores)

1.5

1.51

ity (g

/cc)

1.37

1.38

ity (g

/cc)

1.48

1.49

rage

Den

s

1.48 MPa 1.35

1.36

rage

Den

s

1.48 MPa

1.472/6/11 2/11/11 2/16/11 2/21/11 2/26/11 3/3/11

Aver

Scan Date

2.86 MPa4.24 MPa

1.343/13/11 3/18/11 3/23/11 3/28/11 4/2/11 4/7/11

Ave

Scan Date

2.86 MPa4.24 MPa

C-14 CT-derived density measurements C-25 CT-derived density measurements

The scans show that the majority of this CO2 uptake was occurring within the third of the sample closest to

The dual-energy values used to derive these densities were calibrated to standards g p

CO2 inlet port. The rate of CO2 sorption into the sample slowed when the pore pressure increased to 2.86 and 4.24 MPa. During the entire experiment the confining pressure was held 1.48 MPa greater than the pore pressure

of known density before and after the CO2exposure of the core and showed little change.

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pressure.

Manometric sorption isotherms

Adsorbed amount (Gibbs definition)( )

nGibbs = ntotal – ρgVo; Vo = Va + Vi; Va = nabs/ρa;

Absolute adsorption

nabs = nGibbs (ρa/(ρa – ρg)) (assumed ρa = 1.18 g/cm3)

Langmuir model

V = VL(P/(PL + P))

The Langmuir model was used in order to provide engineering parameters by fitting the absolute adsorption plots.

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RESULTS (sorption on powder)1 2 1 2

0.6

0.8

1

1.2

rptio

n, m

mol

/g C-13

0.6

0.8

1

1.2

orpt

ion,

mm

ol/g C-14

0

0.2

0.4

0 1 2 3 4 5

Abs

olut

e so

Moist at 35 ⁰CMoist at 55 ⁰CDry at 55 ⁰C

0

0.2

0.4

0 1 2 3 4 5

Abs

olut

e so

Moist at 35 ⁰CMoist at 55 ⁰CDry at 55 ⁰C

Pressure, MPa Pressure, MPa

0.8

1

1.2

n, m

mol

/g C-25

0 60.70.80.9

1n,

mm

ol/g C-28

0 60.70.80.9

1

n, m

mol

/g C-29

0.2

0.4

0.6

Abs

olut

e so

rptio

n

Moist at 35 ⁰CMoist at 55 ⁰CDry at 55 ⁰C 0.1

0.20.30.40.50.6

Abs

olut

e so

rptio

n

Moist at 35 ⁰CMoist at 55 ⁰CDry at 55 ⁰C 0.1

0.20.30.40.50.6

Abs

olut

e so

rptio

n

Moist at 35 ⁰CMoist at 55 ⁰CDry at 55 ⁰C

00 1 2 3 4 5

A

Pressure, MPa

00 1 2 3 4 5

A

Pressure, MPa

00 1 2 3 4 5

A

Pressure, MPa

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Summary

Currently, the I2B coal seam in the Charqueadas coal field is NOT recommended for CO2 sequestration but further research is justified.

Positive findings:It was observed that the lower layers of the I2B coal seam have a significant potential for carbon sequestration but only in a powdersignificant potential for carbon sequestration but only in a powder or fractured form.

The upper seam has permeability too low to justify a direct i j ti f b di id H it dinjection of carbon dioxide. However, it may serve as a good secondary seal.

Further research of how the coal properties at this micro-p pscale can be related to the properties observed on the macro-scale will provide insight into how well the Charqueadas I2B coal seam will release methane or adsorb CO2 for geologic storage

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storage.