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Gaseous CO2 migration in the shallow subsurface: Laboratory, Numerical modelling, and Field investigation

Rune Nørbæk Lassen

Karsten Høgh Jensen

Majken Looms

Department of Geoscience, Natural Resources and Planning

Torben Sonnenborg

GEUS

Jacob Gudbjerg

Final project meeting 2014

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Laboratory:

1. Gaseous CO2 migration in a 1D column.

1. Gaseous CO2 migration in a 2D tank.

2. Heterogeneity enhanced exsolution of dissolved CO2 (external partner)

Field:

3. Tracking gaseous CO2 with cross-borehole GPR.

4. Detecting dissolved CO2 with 3D cross-borehole ERT (external partner).

Numerical modelling with T2VOC:

1. Modelling 1D and 2D laboratory experiments.

5. Modelling field experiments.

5. Gas migration control mechanisms.

Papers:

1. Effects of Geologic Heterogeneity on Migration of gaseous CO2 using Laboratory and Modelling Investigations (submitted).

2. Heterogeneity-Enhanced Gas Phase Formation in Shallow Aquifers During Leakage of CO2-Dissolved Water from Geologic Sequestration Sites (submitted).

3. Monitoring CO2 gas-phase injection in a shallow sand aquifer using cross-borehole Ground Penetrating Radar (draft).

4. Monitoring a pilot CO2 injection experiment in a shallow aquifer using 3D cross-well electrical resistance tomography (draft).

5. Modelling of near surface CO2 leakage in the saturated zone (in process).

Activities and achievement



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Paper 1: Laboratory work and modelling


• Macro-scale heterogeneity versus pore-scale heterogeneity • Confining layers • Local equilibrium assumption • Injection and lateral spreading of gaseous CO2. • The applicability of the numerical code for large-scale field experiments.


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Set-up and experiments



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Heterogeneity and injection rate


•The test confirmed our ideas about larger scale heterogeneity controlling overall gaseous CO2 migration in a porous media environment. However dissolution processes and very low flow rates are controlled at micro-scale. •Both the simulations and the experiments displayed that higher injection rates generated larger lateral and vertical spreading of the gaseous phase during the injection. Modelled Measured


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Confining layers


Pressure builds before a barrier is breached. Knowing the location of the capillary barriers is essential for numerical models to predict reliable results. Barrier layers make point measurements very difficult to use outside lab.

Modelled Measured


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Local equilibrium and field scale.


Due to the necessity of a coarser discretization than that of the gaseous flow channels, local equilibrium resulted in an overestimation of dissolved CO2 and delay of the breakthrough curves for the gaseous phase.

Modelled (g/l) Measured


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Paper 2: Heterogeneity enhanced gas-exsolution. M. Plampin, Colorado School of Mines


As the CO2-saturated water flowed across the interfaces between the various types of porous media, a separate gas phase formed and evolved within the pores of the media. The study focused on the evolution of macroscopic gas saturations.


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The definition


Copenhagen 2014

ΔPo = ΔPi + Δpe ΔPi = Psat – Pinj ΔPe = Pe,above – Pe,below


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Example:


Over saturated

Under saturated Heterogeneity enhanced


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Conclusion

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Heterogeneity enhances gas evolution within a predictable range of conditions.

• Transitions from high- to low-permeability significantly affect gas evolution.

• Transitions from low- to high-permeability do not

usually affect gas evolution.


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Paper 3: Field experiment – tracking gaseous CO2


• Next step from controlled laboratory setup. • Cross borehole GPR to detect gaseous CO2 below the groundwater table. • Heterogeneity – lateral flow. • Gas flow and groundwater flow are independent. • Base for multiphase modelling.


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Field site: Location and Setup


Gaseous CO2 injection rate was 15.6 g/minute 29 hours of injection (leakage problems) Cross borehole GPR measurements can be directly converted to water content.


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Background


Geology profile and grain size

Porosity based on GPR


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ZOP – Post injection



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MOG profiles – Post gas injection


Left to right: MOG42 4H, MOG45 4H, Left to right: MOG13 21H, MOG42 27H , MOG45 26H,

Copenhagen 2014


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Stagnation and dissolution


6 8 10 12 14 166

7

8

9

10

11

12

13

14

15

16

1

2

3

4

5

6

The maximum amount of gaseous CO2.

The CO2 dissolves rapidly once the injection has stopped.


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Conclusion


The gas phase was primarily located in two horizons; the lower zone, at 8.5m depth, and the second zone, just below 6m depth. The exception is north and east of the injection, where 6m is the only barrier. Initial spreading of the gas is towards the North and East. Largest amount of gas accumulates 2m south of the injection (sat 0.44). Large quantities of gaseous CO2 most likely migrate away from the survey area.


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Field ERT – pilot experiment X. Yang, Lawrence Livermore National Laboratory

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Evaluating the effectiveness of the 3D ERT method for monitoring the two opposing effects from gas-phase and dissolved CO2 in a shallow aquifer.

• There were 96 electrodes in four ERT boreholes • bipole-bipole electrode -5634 data points (including reciprocal)

• 1% of noisy data • Skip4 dipole-dipole array -13343 data points (including reciprocal)

• 7% of noisy data


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Field site


45 injector

ERT1

ERT2

ERT4

ERT3

Total 17 sample points

GPR1

GPR2

GPR4

GPR3

5 m

5m

1

2

3 4 5

6 8

9 10

11

12

13

14

15

16

17

7

Gro

undw

ate

r flo

w

(0,0)

4.25m

0.75m

N

Copenhagen 2014


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Increase in conductivity versus increase in gas saturation.


8 hours

26 hours

GPR1

GPR2

GPR1

GPR2

49 hours

GPR1

GPR2

3 hours 24 hours 50 hours

GPR1 GPR2 GPR1 GPR2

GPR1 GPR2

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

0.00 0.10 0.20

5hours

26hours

50hours


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Increase in conductivity vs increase in gas sat.

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3 hours

24 hours

50 hours

GPR3

GPR2

GPR3

GPR2

GPR3

GPR2

2 hours

26 hours

49 hours

GPR3

GPR2

GPR3

GPR2

GPR3

GPR2

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

0.00

5hours

26hours

50hours


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Cross section comparison


GPR2 GPR4

0.00 0.10 0.20

26hours

ERT data (24 hours of injection) and CO2 gas content by ZOP GPR data (26 hours of injection) along a cross section intersecting boreholes GPR2 and GPR4.

Copenhagen 2014


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3D time elapse of increased conductivity Enhedens navn

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Conductivity Changes (%) -10 -5 0 5 10

ERT4 ERT3

ERT2 ERT1

ERT4 ERT3

ERT2 ERT1

ERT4 ERT3

ERT2 ERT1

3 hours 24 hours 50 hours

Figure 7. Three-dimensional time lapse changes of electrical conductivity due to CO2 injection. This is the inverted results of Skip4 data sets. The color opacity threshold was set to 4%.



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Conclusions

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• ERT appears to be an effective tool for detection of the “edges” of CO2 plumes in a controlled release. • ERT may not capture the entire

picture of CO2 distribution

• ERT detects leakage long after the gas has dissolved due to tailing effect (increased cond.)

• 3D high-resolution temporal monitoring


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Paper 5: Field modelling and sensitivity

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Matching measured gas saturation from field experiments by employing a radial grid, and using parameters from in-situ sediment samples. Three controlling mechanisms we are investigating further: • Model discretization and especially in relation to entry pressure

values.

• Pockets are not always are the ideal trapping mechanism.

• Inclined low permeability layers on gas phase migration.


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Conceptual model and parameters

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Soil Perm.

[m2]

Entry

pres. [m]

Brooks

and

Corey λ

Residu

al

saturat

ion

1.Very Fine

sand

3.13E-

13

0.95 0.9 0.1

2. Fine sand 8.35E-

13

0.68 1.0 0.1

3. coarse

sand

1.03E-

12

0.30 1.6 0.1

4. Gravel* 1.41E-

12

0.15 1.7 0.1

Injection: 15.6 g/min Boundaries. Constant head

6 m

8.5m

7 m

6 m

8.5m

7 m

6 m

8.5m

7 m


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Four likely scenarios

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2 4 6 8 10 12 14

-6

-4

-2

2 4 6 8 10 12 14

-6

-4

-2

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

2 4 6 8 10 12 14

-6

-4

-2

2 4 6 8 10 12 14

-6

-4

-2

Upper: Left low permeable gravel layer. Right high permeable gravel layer. Lower: Left pocket of high permeable gravel into sand. Right, wedge of sand into highly permeable gravel.


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Discretization

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However: If ∆Pe < ∆Z – entry pressure becomes insignificant. Gas will move upward, and movement will only be limited by difference in permeability.

Boundary layer: For the gas to move from the coarse sand into the fine sand the gas saturation in the coarse sand will have to be above 0.7, where the capillary pressure of the coarse sand equals the entry pressure of the fine sand.


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Pockets – Buoyancy driven flow

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Injectio

n rate

Delta

entry

pressure height

perm

(XY)

breakthro

ugh

overfl

ow

max

Gs

kg/s cm cm m2 <<<<

<<<<

< %

1.E-08 10 15

2.50E-

11 x 64.8

1.E-08 10 15

9.50E-

11 X 64.8

1.E-08 15 15

2.50E-

11 x x 69.2

1.E-08 15 15

9.50E-

11 x x 69.2

1.E-08 20 15

2.50E-

11 x 74.2

1.E-07 10 15

2.50E-

11 x x 70.1

1.E-07 10 15

9.50E-

11 x x 70.1

1.E-07 15 15

2.50E-

11 x x 75.9

1.E-07 15 15

9.50E-

11 x x 75.9

1.E-07 20 15

2.50E-

11 x 76.7

1.E-07 20 15

9.50E-

11 x 76.7


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Inclined two 2D- cross section

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-3

-2

-1

-3

-2

-1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

-3

-2

-1

2 4 6 8 10 12 14 16 18

-3

-2

-1

Test: • Inclination vs. Perm.

• Inclination vs. injec. Rate

• Inject. rate vs. Perm. • Entry pres. vs. Perm.

Example:

Perm. Values: from grain size and pump test.

Inclination: 1-3 degrees Inject. rate Buoyancy (low) Entry pressure from grain size


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Conclusion

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• While it proved impossible to find a unique solution to a specific

case, using modelling as a predictive tool for leakage pathways at a CCS site is extremely difficult, and have to be used with care for risk assessment. This is not the fault of the model but a problem of scaling the local geology.

• You can predict more with a model, than what you know about geology – but you can not know if the predicted solution is accurate for a specific site.

• A very real issue: • Permeability estimated from grainsize are 15-20 times

lower than those measured with a pumptest at the field site.

gaseous co migration in the shallow subsurface: laboratory ...€¦ · teksten, brug forøg...

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