99 Influence of carbon dioxide on coal permeability

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. , Mc. Lendon, 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 1

Outline �Introduction �Objectives �Methods of Study �Results and Discussion �Conclusions 2

Introduction 3

�CO 2 sorption on coal seams induces swelling effect on coal matrix. (Siriwardane et al. , 2006; Mazumder et al. , 2006; Day et al. , 2008) CO 2 coal seam Swelling v. s. Permeability ? 4

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

Objectives 6

�To investigate the influence of CO 2 exposure on coal permeability. 7

Methods of Study 8

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. 9

Experimental procedure Coal sample was fractured (S 01 -S 10) or natural cleats (S 11 -S 14) 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. 10

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

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

Results and Discussion 13

Porosity and permeability of coals Table 1. Porosity and permeability of the coal samples. (CO 2 as pore fluid, Confining pressure : 20 MPa, Pore pressure : 10 MPa. ) Coal sample D (mm) L (mm) Porosity (%) Permeabil ity (initial) (μD) Experime nt time (hr) Permeabilit y (final) (μD) S 01 37. 5 19. 15 1. 40% 10 310 6 S 02 37. 7 51. 1 0. 63% 550 220 250 S 04 37. 5 80. 1 0. 71% 65 265 35 S 05 37. 45 79 0. 62% 62 30 40 S 06 37. 65 67. 6 0. 78% 1500 290 500 S 08 37. 46 77. 1 0. 27% 1 72 0. 05 S 10 50. 37 79. 9 0. 75% 40 95 18 S 11 37. 48 75. 9 0. 35% 0. 09 175 0. 028 S 12 37. 43 53. 25 1. 43% 0. 13 68 0. 07 S 14 37. 7 59. 05 1. 07% 240 70 50 14

Porosity and permeability of coals Table 2. Porosity and permeability of the coal samples. (Ar as pore fluid, Confining pressure : 6 MPa, Pore pressure : 4 MPa. ) Coal sample D (mm) L (mm) Porosity (%) Permeabil ity (initial) (μD) Permeabilit y (final) (μD) S 02 37. 7 51. 1 0. 63% 3000 S 04 37. 5 80. 1 0. 71% 2000 S 05 37. 45 79 0. 62% 2500 S 06 37. 65 67. 6 0. 78% 4500 Table 3. Porosity and permeability after increasing in confining pressure. (CO 2 as pore fluid, Pore pressure : 10 MPa. ) Coal sample D (mm) L (mm) Porosity (%) Permeabil ity (initial) (μD) Permeabilit y (final) (μD) S 02 37. 7 51. 1 0. 63% 200 105 S 04 37. 5 80. 1 0. 71% 35 14 S 06 37. 65 67. 6 0. 78% 150 35 S 10 50. 37 79. 9 0. 75% 8 1. 4 15

Influence of exposure time on permeability (Ar v. s. CO 2) 58% Fig. 8. Variation of permeability with exposure time of argon for sample S 02. Fig. 9. Variation of permeability with exposure time of CO 2 for sample S 02. 16

Effects of confining stress on permeability 65% Fig. 10. Influence of confining stress on the coal permeability for sample S 04. 17

Influence of CO 2 exposure time on permeability of naturally fractured samples 69% 58 % Fig. 11. Variation of permeability with exposure Fig. 9. Variation of permeability with exposure time of CO 2 for sample S 02. time for a naturally fractured sample S 11. 18

Conclusions 19

�The permeability of fractured coal samples decreased significantly with CO 2 exposure time due to the coal swelling. �After long enough exposure to CO 2, the fracture is completely closed due to the coal swelling, and CO 2 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