The paper is dealing with the permeability of coal in triaxial state of stress. The permeability of coal, besides coal’s methane capacity, is the main parameter determining the quantity of methane inflow into underground excavations. The stress in a coal seam is one of the most important factors influencing coal permeability therefore the permeability measurements were performed in tri-axial state of stress. The hydrostatic three-axial state of stress was gradually increased from 5 MPa with steps of 5 MPa up to a maximum of 30 MPa. Nitrogen was applied as a gas medium in all experiments.
The results of the permeability measurements of coal cores from the “Zofiówka” mine, Poland, and three mines from the Czech Republic are presented in this paper. As a “reference”, permeability measurements were also taken for coal briquettes prepared from coal dust with defined porosity.
It was confirmed that the decreasing porosity of coal briquettes affects the decreasing permeability. The advantage of experimentation on coal briquettes is its good repeatability.
From the experimental results, an empirical relation between gas permeability and confining pressure has also been identified. The empirical relation for coal briquettes is in good correspondence with published results. However, for coal cores, the character of change differs. The influence of confining pressure has a different character and the decrease in permeability is stronger due to the increasing confining pressure
ASTM Standards 1990. D 4525. Standard test method for permeability of rocks by flowing air. Annual Book of ASTM Standards, Vol. 04.08, 825-828.
Beamish B.B., Crosdale P.J.,1998. Instantaneous outbursts in underground coal mines: An overview and association with coal type. Int. J. Coal Geol., 35, 27-55.
Cao Y., Mitchell G.D., Davis A., Wang D., 2000. Deformation metamorphism of bituminous and anthracite coals from China. Int. J. Coal Geol., 43, 227-242.
Dopita M., Editor, 1997. Geology of the Czech Part of the Upper Silesian Basin. Prague: Ministry of the Environment of the Czech Republic; 1-278 (in Czech with English summary).
Huy P.Q., Sasaki K., Sugai Y., Ichikawa S., 2010. Carbon dioxide gas permeability of coal core samples and estimation of fracture aperture width. Int. J. Coal Geol., 83, 1-10.
Jasinge D., Ranjith P.G., Choi S.K., 2011. Effects of effective stress changes on permeability of Latrobe valley brown coal. Fuel, 90, 1292-1300.
Kędzior S., 2009. Accumulation of coal-bed methane in the south-west part of the Upper Silesian Coal Basin (southern Poland). Int. J. Coal Geol., 80, 20-34.
Konečný P. Jr, Kožušníková A., 2010. Comparison of coal permeability from 504 seam (Saddle member) and from 080 seam (Petřkovice member) for different gases. [In:] Proceedings of the XXXIII symposium geology of coal-bearing strata of Poland, Krakow, 35-40 (in Czech).
Konečný P. Jr, Kožušníková A., 2011. Influence of stress on the permeability of coal and sedimentary rocks of the Upper Silesian basin. Int. J. Rock Mech. Min. Sci., 48, 347-352.
Konečný P., Jr, Kožušníková A., 1996. Measuring of gas - permeability of coal and clastic sedimentary rocks at triaxial state of stress. Coalbed Methane and Coal Geology. [In:] Gayer, R. & Harris, I. (ed.), Geological Society Special Publication, 109, 227-229.
Kožušníková A., Wierzbicki M., 2009. Comparison of permeability of coal bricquettes from mylonite and undisturbed zones in coal seam 409/4 in “Zofiówka” Coal Mine. Ostrava: Documenta Geonica, 119-128 (in Czech).
Lama R.D., Bodziony J., 1996. Outbursts of gas, coal and rock in underground coal mines. R.D. Lama & Associates, Wollongong, NSW, Australia.
Li H., Ogawa Y., Shimada S., 2003. Mechanism of methane flow through sheared coals and its role on methane recovery. Fuel, 82, 1271-1279.
Martinec P., Jirásek J., Kožušníková A., Sivek M., Editors, 2005. Atlas of Coal - Czech part of the Upper Silesian basin.
Ostrava: Anagram, 1-60 (in Czech with English summary).
Młynarczuk M., Wierzbicki M., 2009. Stereological and Profilometry Methods in Detection of Structural Deformation in Coal Samples Collected from the Rock and Gas Outburst Zone in the „Zofiówka” Colliery. Arch. Min. Sci., Vol. 54, No 2, p. 189-201.
Neset K. et al., 1973. Mining guide. I. part. Praha: SNTL (in Czech).
Rakowski Z., Lát J., Hruzík B., Dvořáček J., 1983. New findings on the issue of coal and gas outbursts in OKR. Praha: SNTL (in Czech).
Wierzbicki M., Dutka B., 2010. The influence of temperature changes of the structurally deformed coal - methane system on the total methane content. Arch. Min. Sci., Vol. 55, No 3, p. 547-560.
Wierzbicki M., Młynarczuk M., 2006. Microscopic Analysis of Structure of Coal Samples Collected after Gas and Coal Outburst In the Gallery D-6, Coal Seam 409/4 in the “Zofiówka” Coal Mine (Upper Silesian Coal Basin). Arch. Min. Sci., Vol. 51, No 4, p. 577-588.
Wierzbicki M., 2003. Changes in the stress and effort of the material in the course of provocation and initiation of rock and gas outbursts in laboratory conditions. IMG PAN Krakow, Rozprawy, monografie, 4 (in Polish).
Zhang G., 1995. Area prediction of danger of coal and gas outbursts - example of application in Jiaozuo mining area in China. Int. Symp. - Workshop on Management and Control of High Gas Emission and Outbursts in Underground Coal Mines (Ed. Lama) Wollongong, NSW, 20-24 March, 195-199.