The Depositional Relationship Between Sand and Coal in the Permian Patchawarra Formation in the Coonatie Feild, Cooper Basin
Fakhruddin Afif Fauzi
Honours Degree 2010
University of Adelaide
Sandstone formations in the Permian section in the Coonatie Field of the Cooper Basin are predicted from geophysical seismic amplitudes descriptions. Within the Patchawarra Formation, problem arises where coals dominate the seismic signature, while sandstones show only a minor secondary impact of the seismic amplitudes.
Two hypotheses were proposed to relate the depositional relationship between sand and coal in the Patchawarra Formation. The first hypothesis suggests that peat bogs grow as elevated peat mires and resistant to physical erosion, hence effective in maintaining the focus of sand deposition around their margins. The second hypothesis states that coal compaction focuses the deposition os the channel sands. As sand undergo less compaction than coal, sand channels will seek the lower topography generated by coal. The aim of this study is to test whether hypothesis 1, hypothesis 2, both or neither can be used to describe the depositional relationship between sand and coal, based on sand-to-gross and coal-to-gross distributions.
In the Coonatie Field, the Patchawarra Formation was divided into four intervals based on selected chronostratigraphic units of VU45, VU75, VC90 and XU00. Literature reviews of the Patchawarra Formation showed that it was deposited in fluvial meandering channel systems in a N to NE direction. Coal was deposited as either low-lying swamps or high-latitude raised swamps. Analysis of Coonatie well data revealed that the Patchawarra Formation was deposited in two Transgressive System Tracts. Thick sands appeared in the Top Patchawarra-VU45 and VU75-VC90 intervals. Thick coals occurred in Top Patchawarra-VU45 and VU75-VC90 intervals. Sand-to-gross was lower than coal-to-gross towards the youngest interval, and vice versa. The Coonatie Field 3D seismic data showed that major faults occurred during the deposition of the Patchawarra Formation.