1

CO2 storage and gas diffusivity properties of coals from Sydney Basin, AustraliaA. Saghafi, M. Faiz , D. Roberts

報告者 : 藍一平指導老師 : 蔡龍珆 老師日期 : 2011/05/26

International Journal of Coal Geology , 70, 240–254

2

OUTLINE

Introducti on

Objecti ves

L iterature Review

Methods

Result and Discussion

Conclusions

3

INTRODUCTION

4

Exploration of boreholes involves investigations on factors affecting CO2 storage and injection, in particular the adsorption and diffusivity properties of coal.

One particularity of Australian coalfields is the occurrence of large amounts of CO2 in many coal seams.

extraction well

(http://www.zybsh.cn/zs/ytgk/index.htm)

5

Clayton (1998) listed four sources for CO2 gas in coal seams:

CO2 in Sydney Basin coals is mainly derived from magmatic sources as the high CO2 content areas generally have isotopic compositions of δ13C of about −7‰. (Smith and Gould, 1980; Smith et al., 1985)

Decarbox-ylation

reactions

Mineral reactions

Bacterial oxidation

Magmatic intrusion

6

150 Mt / year of coal

Hunter, Newcastle, Western and Southern coalfield

Permian-Triassic

Medium to high volatile bituminous

Open-cut mining

Fig. 1. The major coalfield in Sydney Basin, NSW (http://www.csmenergy.com.au/operations.html)

Study Area

Hunter Coalfiled

Newcastle CoalfiledWestern Coalfiled

Southern Coalfiled

7

OBJECTIVES

8

The aim of the present investigation is to characterize Sydney Basin coals according to two parameters (adsorption and diffusivity), particularly for CO2.

9

LITERATURE REVIEW

10

In-situ coal contains gas

free phase

adsorbed phase

• micro-pore• Langmuir equation

• macro-pores

(Langmuir, 1918)

11

Sorption

Diffusion

Convection

(Saghafi et al., 1987)(Remner et al., 1984)

IUPAC

Macroporous > 50 nm

Mesoporous 2~50 nm

Microporous < 2 nm

13

METHODS

14

Adsorption isotherm

The technique developed to measure adsorption isotherms is based on a gravimetric method. (Saghafi, 2003)

Fig. 2. Schematic diagram of gravimetric adsorption measurement apparatus.

15

Measurement method for gas diffusivity

Fick's equation :

Fig. 3. Schematic diagram of measurement apparatus for gas diffusivity in coal.

Ψdthe gas diffusive flux

Dethe effective diffusion coefficient

c the gas concentration

x the space dimension

P1 = P2

C1,1 > C2,1

16

RESULT AND DISCUSSION

17

Coal sampling and measuring conditions

R0 (max, %) 0.66~1.45

Moisture(%) 0.4~7.9

VM (daf, %) 21~43

Ash(%) 5~34

Contact metamorphosed

18

Adsorption isotherm measurements (1)

Fig. 4. Measured adsorbed volume versus Langmuir estimated volume for CO2 adsorption.

Fig. 5. Relative error (r) in using a Langmuir type equation for determining CO2 adsorption for all coals studied.

19

Adsorption isotherm measurements (2)

Fig. 6. CO2 Langmuir volume VL for the Sydney Basin coals in relation to volatile matter content (VM).

Fig. 8. CO2 adsorption capacity of the Sydney Basin coals according to the rank

Fig. 7. Langmuir pressure (PL) in relation to volatile matter content.

no clear relationship

20

Adsorption isotherm measurements (3)

Fig. 9. CO2 storage capacity of the Sydney Basin coals at in-situ pressure

C0=30.1 m3/t h0=400 m a=0.56

21

Diffusivity and porosity measurements

Fig. 10. CO2 diffusivity and coal porosity according to depth.

Fig. 11. CO2 diffusivity and porosity according to volatile matter content

no clear relationship

22

Comparison of properties of main seam gases

Fig. 12. Adsorption of pure CO2, CH4 and N2 on coal (coal17).

CO2/CH4 : 1.8

CO2/N2 : 5.9

23

CONCLUSIONS

24

The highest adsorptive capacity corresponds to the deepest, highest rank coal, the lowest corresponds to a shallower coal but not necessarily the lowest rank coal.

For these samples, no clear relation between the diffusivity and the depth or rank of coals.

The CO2 storage capacity is about twice that of CH4 and six times that of N2. The diffusivity of CO2 in coal is about twice that of CH4.

25

Thanks for Your Att enti on!