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99學年度第二學期專題討論

Influence of carbon dioxide on coal permeability determined by pressure transient methods Siriwardane, H., Haljasmaa, I., McLendon, R., Irdi, G., Soong, Y., Bromhal, G., 2009. Influence of carbon dioxide on coal permeability determined by pressure transient methods. International Journal of Coal Geology, 77, 109–118.

Adviser： Loung-Yie Tsai

Presenter： Ling-Szu Wang

Date： 2011/6/9

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OutlineIntroductionObjectivesMethods of StudyResults and Discussion

Conclusions

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Introduction

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CO2 sorption on coal seams induces swelling effect on coal matrix. (Siriwardane et al., 2006; Mazumder et al., 2006; Day et al., 2008)

Swelling v.s. Permeability ?

CO2

coal seam

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Coal seams include matrix and fracture areas .

Diffusion is a very slow process that occurs in the coal matrix, and flow of fluids takes place in the fracture system.

Fig. 1. Diagram of matrix and fractures. (Huy et al., 2010)

Pressure v.s. Permeability ?

Fracture v.s. Permeability ?

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Objectives

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To investigate the influence of CO2 exposure on coal permeability .

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Methods of Study

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Experimental procedurePreparing core samples of coal.

Measuring porosity.

Jacketing coal sample.

Fig. 2. Helium porosimeter, HP-401. (TEMCO, Inc.)

Fig. 3. A typical fractured coal core sample in a rubber jacket.

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Experimental procedureCoal sample was fractured (S01-S10) or

natural cleats (S11-S14)

were used.

Taking CT scans before and after

each test.

Determining permeability.

Fig. 4. Diagram showing the induced fracture through a coal sample.

Fig. 5. CT scan of a fractured coal sample.

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Determining permeability

Fig. 6. Autolab 1500, from New England Research, Inc. (NER, 2005)

12Fig. 7. Schematic diagram of the pressure transient method.

Pressure transient methodFor measuring permeability of tight rocks. (Brace et al., 1968; Hsieh et al., 1980; Kamath et al., 1990; Evans and Wong, 1992.)

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Results and Discussion

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Table 1. Porosity and permeability of the coal samples. (CO2 as pore fluid, Confining pressure : 20MPa, Pore pressure : 10MPa.)

Porosity and permeability of coals

Coal sample

D(mm)

L(mm)

Porosity(%)

Permeability (initial)(μD)

Experiment time (hr)

Permeability (final)(μD)

S01 37.5 19.15 1.40% 10 310 6

S02 37.7 51.1 0.63% 550 220 250

S04 37.5 80.1 0.71% 65 265 35

S05 37.45 79 0.62% 62 30 40

S06 37.65 67.6 0.78% 1500 290 500

S08 37.46 77.1 0.27% 1 72 0.05

S10 50.37 79.9 0.75% 40 95 18

S11 37.48 75.9 0.35% 0.09 175 0.028

S12 37.43 53.25 1.43% 0.13 68 0.07

S14 37.7 59.05 1.07% 240 70 50

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Table 2. Porosity and permeability of the coal samples. (Ar as pore fluid, Confining pressure : 6MPa, Pore pressure : 4MPa.)

Porosity and permeability of coals

Coal sample

D(mm)

L(mm)

Porosity(%)

Permeability (initial)(μD)

Permeability (final)(μD)

S02 37.7 51.1 0.63% 3000 3000

S04 37.5 80.1 0.71% 2000 2000

S05 37.45 79 0.62% 2500 2500

S06 37.65 67.6 0.78% 4500 4500

Table 3. Porosity and permeability after increasing in confining pressure.

(CO2 as pore fluid, Pore pressure : 10MPa.)

Coal sample

D(mm)

L(mm)

Porosity(%)

Permeability (initial)(μD)

Permeability (final)(μD)

S02 37.7 51.1 0.63% 200 105

S04 37.5 80.1 0.71% 35 14

S06 37.65 67.6 0.78% 150 35

S10 50.37 79.9 0.75% 8 1.4

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Influence of exposure time on permeability (Ar v.s. CO2)

Fig. 8. Variation of permeability with exposure time of argon for sample S02.

Fig. 9. Variation of permeability with exposure time of CO2 for sample S02.

58%

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Effects of confining stress on permeability

Fig. 10. Influence of confining stress on the coal permeability for sample S04.

65%

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Influence of CO2 exposure time on permeability of naturally fractured samples

Fig. 11. Variation of permeability with exposure time for a naturally fractured sample S11.

69%

Fig. 9. Variation of permeability with exposure time of CO2 for sample S02.

58%

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Conclusions

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The permeability of fractured coal samples decreased significantly with CO2 exposure time due to the coal swelling.

After long enough exposure to CO2, the fracture is completely closed due to the coal swelling, and CO2 transport in the sample occurs only by diffusion through the coal matrix.

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The higher confining pressure appears to close internal fractures causing a reduction in permeability.

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Thanks For Your Attention.