99 學年度第二學期專題討論 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., 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 1

Outline Introduction Objectives Methods of Study Results and Discussion Conclusions 2

Introduction 3

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 ? 4 CO2 coal seam

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. 5 Fig. 1. Diagram of matrix and fractures. (Huy et al., 2010) Pressure v.s. Permeability ? Fracture v.s. Permeability ?

Objectives 6

To investigate the influence of CO2 exposure on coal permeability. 7

Methods of Study 8

9 Experimental procedure Preparing 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.

10 Experimental procedure Coal 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.

Determining permeability 11 Fig. 6. Autolab 1500, from New England Research, Inc. (NER, 2005)

Fig. 7. Schematic diagram of the pressure transient method. 12 Pressure transient method For measuring permeability of tight rocks. (Brace et al., 1968; Hsieh et al., 1980; Kamath et al., 1990; Evans and Wong, 1992.)

Results and Discussion 13

Table 1. Porosity and permeability of the coal samples. (CO2 as pore fluid, Confining pressure : 20MPa, Pore pressure : 10MPa.) Porosity and permeability of coals 14 Coal sample D (mm) L (mm) Porosity (%) Permeabil ity (initial) (μD) Experime nt time (hr) Permeabilit y (final) (μD) S % S % S % S % S % S % S % S % S % S %

Table 2. Porosity and permeability of the coal samples. (Ar as pore fluid, Confining pressure : 6MPa, Pore pressure : 4MPa.) Porosity and permeability of coals 15 Coal sample D (mm) L (mm) Porosity (%) Permeabil ity (initial) (μD) Permeabilit y (final) (μD) S %3000 S %2000 S %2500 S %4500 Table 3. Porosity and permeability after increasing in confining pressure. (CO 2 as pore fluid, Pore pressure : 10MPa.) Coal sample D (mm) L (mm) Porosity (%) Permeabil ity (initial) (μD) Permeabilit y (final) (μD) S % S %3514 S %15035 S %81.4

Influence of exposure time on permeability (Ar v.s. CO2) 16 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%

Effects of confining stress on permeability 17 Fig. 10. Influence of confining stress on the coal permeability for sample S04. 65%

18 Influence of CO2 exposure time on permeability of naturally fractured samples Fig. 11. Variation of permeability with exposure time for a naturally fractured sample S % Fig. 9. Variation of permeability with exposure time of CO2 for sample S %

Conclusions 19

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. 20

The higher confining pressure appears to close internal fractures causing a reduction in permeability. 21

Thanks For Your Attention. 22