Geological Appraisal of the Walloway Basin, South Australia: Implications for the Potential for Underground Coal Gasification
Steven A. Kwitko - 2009
Bachelor of Science (Petroleum Geology & Geophysics)
Australian School of Petroleum,
The University of Adelaide
The Walloway Basin is an intramontane Tertiary basin 255 km north of Adelaide, within which
Linc Energy seek coal seams suitable for underground coal gasification (UCG). Linc Energy
undertook an exploration program in the Walloway Basin in August 2009 consisting of five
wells, including one partially-cored geotechnical well. The aim of the exploration program, in
which the author participated, was to develop an understanding of the Tertiary stratigraphy of the
basin; to constrain coal occurrence, and; to assess the technical feasibility of UCG.
This study utilised drill cuttings, core and geophysical logs from the exploration program to
evaluate the stratigraphy, lithology, coal occurrence and hydrogeology of the Walloway Basin.
The Tertiary succession has been shown to comprise two main units, a lower fluvial sequence of
interbedded clay, silt, sand and coal and an upper unit comprising lacustrine clays. The lower
unit is itself divided into a basal interval characterised by highly variable carbonaceous
sediments and coal, and an upper interval of non-carbonaceous clay with interbedded sand.
Using a combination of drill cuttings descriptions and geophysical log response, these Tertiary
units are readily correlated between all the wells drilled, and well log correlations have been
produced, which will provide a detailed framework for further exploration and evaluation.
A laterally continuous coal seam (the Walloway Seam) was intersected in all exploration wells,
ranging in thickness from 8 m to 20 m at depths of between 203 m and 295 m, suggesting a
significant coal resource of an ideal thickness and depth for UCG. The coal is low rank, brown
coal (Lignite B) of suitable quality for gasification.
A detailed understanding of the hydrogeology is essential to the success of UCG as the
groundwater system provides the containment of the UCG process and supplies the water needed
for the gasification reactions. A hydrogeological assessment has identified previously
unrecognised potential aquifers and enabled the development of a conceptual hydrogeological
model. The Walloway Seam appears to be hydraulically isolated from surrounding aquifers
based on geophysical log interpretation, which is necessary for optimal UCG efficiency and to
reduce environmental risks.