Publication Name: PESA's Eastern Australasian Basin Symposium II
Authors: S. Scott, B. Anderson, P. Crosdale, J. Dingwall and G. Leblang
Date Published: December 2004
Number of Pages: 28
Reference Type: Book Section
Abstract:
Investigation of the coal seam gas potential of the Walloon Subgroup in the Surat Basin commenced 10 years ago but concerted drilling to prove its economic viability has only been active for the last three years.Core, exploration and appraisal drilling over the last three years have targeted the Juandah (upper) and Taroom (lower) Coal Measures of the Walloon Subgroup. These wells have shown that the low-rank, sub-bituminous, perhydrous coals of the Walloon Subgroup have gas contents of between 1.15-13.17 m 3/t.
During this investigatory work to determine the coal seam characteristics of the Juandah (upper) and Taroom (lower) Coal Measures of the Walloon Subgroup it became obvious that the present stratigraphic framework was not adequate. A review of the stratigraphic nomenclature within the Surat Basin showed that the Walloon Coal Measures had been raised to subgroup status in 1981 but this revision had been rejected in 1997. The authors are confident that the original revision was valid and have proposed this revision with some minor changes and additions.
The recent work has confirmed the initial supposition that the coals within the Walloon Subgroup contain sufficient quantities of gas to be economically viable as a coal seam gas source. Coal volumes, depth and structure have also been confirmed from the initial work. The other characteristics of the Walloon Subgroup that were not known before the recent work are the saturation and permeability of the individual coal intervals. Saturation within the Juandah and Taroom coal intervals varies considerably across the eastern Surat Basin. This saturation does not seem to be dependent on coal petrology but may be determined by structural and stratigraphic features of the Surat Basin.
Permeability also appears to be dependent upon basinal structural features. The coals in general are well cleated, and the cleats contain little or no mineral matter, and a number of prospects have displayed permeability of up to 500 mD. These prospects are located on the Undulla Nose, a broad, gently dipping structure leading out of the basin's axial trough.