Document Type

Conference Paper

Publication Date


Publication Details

I. Gray, Stresses in Sedimentary Strata, including Coals, and the Effects of Fluid Withdrawal on Effective Stress and Permeability, 11th Underground Coal Operators' Conference, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 2011, 297-306.


This paper describes the methods which can be used to determine the in-situ stresses in sedimentary strata including coals. It also examines the changes in effective stresses brought about by fluid withdrawal such as that caused by gas and water drainage. These changes in effective stress are brought about directly by changing fluid pressure and, in the case of coals, by the effects of shrinkage as the coal releases gas and if it dries out. As the permeability of coal is very significantly affected by its effective stress the drainage of coals is dependent on the state of effective stress. Coal permeability may either increase or decrease during drainage. Permeability frequently shows some initial decline as fluid pressure decreases before shrinkage effects cause an increase. In some cases though, the overall trend is for a continuing decline in permeability. Under these circumstances no amount of stimulation to induce drainage will work and some other means must be sought to de-stress the coal. This has typically been by working an adjacent seam which is more amenable to being mined.