The Anisotropy and Inhomogeneity of Coal Permeability and Interconnection of Adjacent Seams

Gray Ian (2015). The anisotropy and inhomogeneity of coal permeability and interconnection of adjacent seams. SPE-177007-MS. SPE Asia Pacific Unconventional Resources Conference and Exhibition, Brisbane, Australia, 9-11 November 2015.


The purpose of this work was to develop a method by which the anisotropy and inhomogeneity of permeability of coal seams and other reservoirs could be rapidly determined at exploration stage. As inhomogeneity can only be determined by multiple tests and anisotropy can only be found by some form of interference test, the intention was to develop an efficient combination of the two.

This was achieved by using drill stem testing (DST) multiple seams in a single borehole followed by the installation of pressure transducers in the coal seams. Another hole was then drilled and DST tested and the transient response in the transducers measured. This was again followed by transducer installation and the drilling of another hole which was then DST tested. Also tested was the interconnection of seams across thin mudstones and a tuff band. The transducer installation was accomplished using cemented in transducers with the cement being displaced in the vicinity of the transducer to establish connectivity with the formation.

The results of the work showed that in the test site inhomogeneity dominated over anisotropy and that the interburden between the seams was highly impermeable. Reliable permeability measurements were achieved by analysing transients of less than 6 kPa (0.86 psi) from a pre and main flow DST.

This process was quick to implement and therefore of low cost. The number of measurements achieved was higher than would have come from a conventional interference test. The multiple boreholes in which flow took place avoided the problem of a conventional interference test, with a single producing hole, which may have been located in a geologically unusual setting.

Author: Ian Gray
Ian initially worked in Australia supervising the installation of the first gas drainage system at Central Colliery and then went on to work as Senior Geotechnical engineer building a mining wing to the consulting company DJ Douglas and Partners. In 1990 he became Principal Engineer, Mining Research with the Safety In Mines Testing and Resarch Station of the Department of Resource Industries of the Queensland Government. In this role he worked on frictional ignitions, mine explosions, windblasts, gas drainage and directional drilling including the first surface to in-seam operation in the country in 1991. In 1994 he started Sigra as a one man business. Since then the company has grown under his guidance to span mining, gas, civil, geotechnical work and a number of mechanical and electronic product developments.

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